Thank you so much for the above info! I tried to include more in my original message but was limited in character space. Yes, very annoyed that our kitchen designer failed to mention this since it was implemented in our town last October (5 months prior to demo!). No use crying about it now so moving forward...

Our architect is recommending the following Broan vent models:

10" hood vent that will feed into this roof cap http://www.broan.com/products/product/1e408a7d-62f1-4d4a-9a6b-57bbb795e25b

8" - 10" vent that will feed from outside of house covered by this wall vent: http://www.broan.com/products/product/b8695201-5aef-4d3c-a0b5-a0562bdac5c2

And fresh air wall damper http://www.broan.com/products/product/589c7448-7ade-42f1-bb3a-a63aceebfe33

Trying to figure out the least obtrusive location for the inside fresh air vent location. Being inside the kitchen would not be ideal (especially in winter) so wondering if it could be placed in the mudroom area behind the kitchen or in the front foyer just off the kitchen in either ceiling or wall. I believe the internal vent cover dimensions will be 13"x13". I think 3ft x 3ft would be too large for either of these spaces. Was also wondering if the vent could come in through wall under cabinet (like a toe kick heater)

The 3 x 3 diffuser is intended to aid laminar flow into my hallway; it is not a requirement in general.

Only the Broan damper is likely to open without causing a pressure loss. Ideally, the external cap would be relatively free to air flow. The two referenced caps appear to me to be intended to see fan pressure and open outward. Operated backwards (assuming that they could so operate) might lead to some pressure loss.

The Broan damper notes refer to "fresh air wall caps," and the MD10TU installation instructions do include these two caps among the listed options. But these options are for the hood cap -- NOT the MUA Cap -- to increase the hood exit duct pressure such that the MD10TU sensor will see pressure when the hood is operating. (Added duct pressure will reduce hood CFM due to the nature of the blower's fan curve.)

For an MUA wall cap, something shaped more or less like the 437, but gutted of any blocking louvers, and just keeping a critter screen might work to keep out the weather while providing a good sized aperture. Whatever is selected needs to easily mate to the duct that fits the MD10TU with low loss.

Dumping this cold air into a mud room or foyer begs for a powerful electric supplemental heater either in the duct, or in the room. See picture of cooksnsews duct heater layout well down this thread:

http://ths.gardenweb.com/discussions/2266424/does-this-sound-right-re-mua

(I had additional pictures of this from cooksnsews, but they seem to have become some form of no longer recognized jpg, and I can't open them.)

On dumping the MUA through a toe kick aperture: This can work, but feet will be cold unless adequately booted (there was a thread about that once) or the MUA is adequately heated.

In commercial kitchens, typically hot even in winter, unheated MUA can be ducted down behind the cooking appliance and dumped onto the floor where it will flow around the (usually poorly insulated) hot appliance and rise into the hood. This may be difficult to configure in a residential kitchen, and some residential ranges prohibit this practice.

The details of implementing these options may be affected by the balance between pacifying code enforcement and addressing safety, if applicable.

Unless your architect is consulting with a HVAC specialist, I recommend you consult with one.

kas

Just read through the cooksnsew's thread! Very informative. Thank you for the link. Will reach out to the HVAC guys we used to install new AC units. They also service our furnace so will ask them about connecting into the furnace to heat incoming air.

You can connect to the furnace to distribute the MUA throughout the house, but before assuming that it can heat what may approach 900 CFM of very cold air in your case, you might want to find out how many BTU/hr your furnace can supply to this air.

For example, 900 CFM is 54,000 CF/hr being raised as much as 50 degrees (more in N. Minnesota). This would be equivalent to a house volume (assuming no leakage) of 270k cu. ft. being heated 10 degrees per hour. A 27,000 square foot house with 10 ft ceilings would be of this volume. Lacking a Bill Gates' house sized furnace, you may need supplemental heating.

Note: Houses with oil burner fired hydronic heating boilers that also heat hot domestic water tanks, and which are sized for largish houses in the north, may be able to divert enough heat to a heat exchanger by prioritizing it, but showering at the same time may have limited time duration unless the water tank is prioritized ahead of the heat exchanger. In that case, the MUA heating will be intermittent.

Also, your A/C may struggle to cool this much air in the summer, but that is not as annoying, I think, as cold air pouring onto occupants who may be sensitive to cold.

kas

Our furnace is an oil burner fired hydronic model that also heats the hot water. The house is roughly 3800sq ft (includes basement which is not heated or air conditioned). I think it would be much more preferable to have A/C struggle a bit than to have cold NE winter air coming into the house which already feels a bit drafty (built '71) so not sealed up as tight as today's builds.

So, I seem to have misunderstood your meaning of 'connecting' in the context of the furnace. Yours is not a circulating air furnace as I imagined, so instead of connecting the MUA air to the furnace, we want to connect the furnace boiler water to a heat exchanger within the MUA ducting or to space heat the room where the MUA duct terminates to warm the MUA before it spreads into the rest of the house. I imagine another circulating pump, thermostat, and heater would be feasible in this context. Various hydronic blown heaters are sold by Grainger, (up to 261k BTU/hr); I have an older more modest one in my garage.

kas

curious what you wound up doing for MUA? I was just thinking about the prospect of routing it through my toekick heater under the sink as well (which was how I came upon this thread while researching). I dont expect the toekick to actually be able to heat the air as it passes through but its the only vent we have to work with since our heating is baseboard hot water and we lack AC. It also has the benefit(?) of being in the kitchen not far from the range, so the cold air should be coming in near someone who is cooking over a hot stove. In this configuration, I would have the mua in the basement, and run a duct all the way across the basement ceiling, and hten it would pop up under the sink into the toekick. So traveling this distance in the duct could either create a cold "stripe" across the floors upstairs, or provide a means to slightly, passively temper the air before discharging into the house? Or maybe neither.

Another thought I had was putting a vent into the small (5'x2' reach-in) pantry we are building as part of this renovation. Assuming closed doors, the pantry would be a space where cold air wouldnt be terribly annoying to people in the house as it is out of the way in a small hallway shared with a bathroom and the entrance to the house (through the garage).

Kaseki, you also had a comment above about discharging the MUA above the hood/range. This would really be ideal IMO because the cold air would not just freeze your feet, but would mix as it falls with the warm air being generated by the cooking activities. I am planning on having a ~42" canopy wall mounted hood with a 4"-6" riser above it to the 8' ceilings. I dont know if there is such a vent but I am imagining a stainless (so as to match the hood somewhat) say 24"? 30"? wide by....something narrow 3"? 4"?, vent in the ceiling just in front of the riser. The ducting in this scenario could be run up through the attic along with the hood ducting....only real downside (other than trying to find such an aesthetically pleasing duct as the one I described and invented in my mind) would be that I would feat when not using the ventilation system, the lack of insulation where the MUA is connected to the outside would result in cold air perpetually coming down this duct into the middle of our kitchen which we are trying to keep warm. It seems this would be less of an issue in the aforementioned horizontal ducting scenario through the basement.

In my opinion, the easiest scheme is allowing (via passive or motorized dampers) MUA into a basement (or mud room or even pantry) which is supplied with a sufficiently powerful (see chart) heater. This preheats the air before it is allowed via ducting or floor register or doorways to enter the kitchen.

A ceiling introduction into the kitchen, if aimed away from the cooktop/range, can also work. But do not be fooled that the air would be heated by the cooking process unless one is running a bank of wall ovens. The heat from the cooktop is an integral part of the cooking plumes rising into the hood and cannot be allowed to be disturbed by interaction with the MUA. The MUA has to replace it around the boundary of the cooktop. This means preheat the MUA or expect a cold draft.

Another consideration is that the velocity of the MUA in a duct, or even a toe kick, will be proportional to the velocity in the hood duct based on their relative cross-sectional areas. In other words, higher than one wants. Plan on using more than one toe kick section if you go in that direction unless your hood CFM is modest.

Overall, to keep the MUA pressure loss minimized, one either has to use a blower that is controlled off of the hood blower or some pressure measurement, or a very unrestrictive MUA path. This limits MUA filtering and any hydronic heat exchanger (radiator) in the path. Hench my suggestion of a basement heater that can blow heat into the room as the MUA travels across it to wherever it is allowed into the kitchen. The MUA intake could be a 10-inch damper short duct section, or something larger.

There are so many issues affecting where one can retrofit the MUA into the house that the best way to evaluate options is to keep in mind the need for low pressure loss and low turbulence in the kitchen. Everything else is optional.

For the purpose of the chart below, assume that your actual hood flow rate is 2/3 of the blower's rated flow rate. Each line is for a different differential temperature between outside and inside that the heating has to make up. [Click to enlarge.]

Kaseki....any reason one couldnt or shouldnt pull MUA in from their attic? Its not potentially toxic like the garage (AFAIK) it has ample ventilation with the soffit vents, would allow me to easily put an insulated cap over the inlet if cold air was pouring down into the house in (and the hood wasnt needed on high), and I dont have to punch another hole in my roof/wall?

Also as I believe you have the fantech silencer and a wolf hood...I had a couple questions (mostly about the silencer). Can it be sealed into a wall/ceiling? Or am I going to need to access it for some reason? Can it break and need to be replaced/repaired? Or if it just pipe basically?

And finally(ish) I have 8' ceilings and am looking to mount a 42/36x18x24 canopy hood, 36" over the range. This leaves me with only ~6" between the top of the canopy hood and the bottom of the sheetrock. The chase I wanted to put the vent through in the bathroom above the kitchen is offset from the center of the range hood by about 6/8 inches....meaning I would like to be able to go from the center of the hood to the left (or right) about 6-8" before going up through the joists...or as I go up through the joists...from there it would be a straight shot to the attic ~12' and then some kind of angle so the exhaust can be out the side of the house and not the roof. Any thoughts/insights on how or if this ducting will come together? Like what pieces/adapters I would need or if its just not going to fit?

At present, I pull my MUA from from my attic, which is open to the outside via soffit vents (larger mesh than usual size stainless steel screening), the down-blast fixture intended to be tied into the MUA system, and whatever can be pulled through the ridge vent. The attic to living space interface is a roughly 2 x 2 foot hydronic heat exchanger above a hall ceiling and the aforementioned 3 x 3 ft diffuser (blades aimed toward kitchen) below the hall ceiling. This configuration is presently performing as a passive MUA. While the hydronic loop is controlled by an air thermostat at the register and a freeze safety thermostat on the heat exchanger plumbing, the intended MUA pressure regulation loop is not completed, as I still have to get Fantech involved with motor, motor controller, and filter caddy. Too many conflicting projects.

Note that my oil burning furnace is provided its own MUA, and its exhaust is effectively sealed from leakage into the house.

My 10-inch hood vent duct uses a Fantech silencer, as does my 8-inch auxiliary ceiling register system. These silencers are about 4-inches larger than the duct size. See Fantech's site for dimensions. The silencers are mounted in the attic, along a tilted duct path from the kitchen to the locations of the two blowers on the roof. If you need to put the silencer in a room on the way to the attic because an extended path in the attic is infeasible, then it would need to be in a chase. Access to the silencer for residential use is not required, but is recommended. However, it should be possible to pull it up from the attic under some conditions. Ducts and duct parts and silencers should be installed so grease runs down without flowing into a duct joint. (Flowing grease would be unlikely for most home owners.)

I use some Fantech adapters, mainly dampers and clamp type duct couplings, which are convenient to use and probably essential for connecting to the silencers.

What I haven't mentioned yet, but which is essential for most attics, is filtering. Outside air can be filtered or not depending on one's tolerance for dust, bugs, or things that eat bugs. Attic fiberglass insulation, however, is not safe to breath. Presently I use a 3M furnace filter over the heat exchanger. When the system is complete, this will morph into caddy-contained 2 x 2 ft 4-inch pleat filter to reduce pressure loss.

The present filter achieves an unexpected result. The difference in pressure between my attic and the house interior with the various household fans and blowers off is too slight for either cold air to settle down into the living part of the house, or for heat to rise up into the attic and be wasted. Of course, with fans on, cold air is pulled down until the air thermostat in concert with the furnace provide the heat exchanger with hot boiler water.

The filter without an MUA blower can for high hood blower settings cause a pressure loss, probably greater than I would like, but I can still successfully collect the cooking plumes that we have generated so far.

Two issues will influence the degree of success of my intended MUA system: (a) the size (CFM) of the blower that I can get into the attic without disassembly, and (b) the ability of the intended Fuji P-I-D controller to auto-find the feedback gains that provide reasonable minimal house differential pressure without hunting. (I.e., getting the system poles into the l.h.p. without making the system terribly numb.)

I may miss providing some answers here, so let me know.

The silencer will never break until you are the victim of a meteor strike or greater misfortune. I don't know its lifetime for needing cleaning due to lint and grease accumulation over the years.

Duct pieces are available to achieve compound angles and offsets. They just need adequate length.

I can't telepathically address fit.

Hey @kaseki, is there a way I can direct message you?

It seems Houzz doesn't provide that capability, or at least I haven't found it. I vaguely recall that one could do so on the Garden Web. The number of other sites I have membership in under the kaseki handle that also provide blind messaging are few and are pretty narrowly focused; e.g., the Pentax forum.

Great thread. I am looking to build a new house with island range hood. What does everyone think about mua into unfinished basement with a grill connecting to finished basement all open to switch back stairs that rise into kitchen living room? I am thinking powered and heated mua from Fantech. I see this giving the MuA more chance to mingle with household air and not dump cold air on anyone directly.

So long as no doors can be closed blocking the MUA path, I would have no objection. MUA heating needs to be adequate for the environment, either by deliberate heating of the MUA while ducted, or by excess heating power included in the unfinished or finished basement spaces. See earlier graph.

Thanks for the feedback - ideally air would be provided via a powered MAU unit with heating elements (Fantech has one) and dump into a 800 SF area of basement (unfinished furnace room) and the furnace room would have a large grill/grate (sized appropriately) to large finished basement area of about 800 SF; no possible door blockage. Will run it by HVAC guy when i get to that stage. I know my furnace area today stays a bit warmer due to furnace and water heater, so couple that with heated MAU, and i think that is about all i can do.

We redid our kitchen last summer and live in the cold northeast. Our contractor wouldnt touch our ventilation plans because of the need for makeup air systems etc...so we did it ourselves.

Wont pass in most places because its not up to code...but functionally, we open the window over the sink (~6' from the hood) and it has worked really well for us. I actually love the cool air that gets sucked in and cools me off while cooking, and im glad it is coming in right near the rangetop and not the other side of the house where I have the cost (installation and operation) of heating it...or dealing with my complaining wife :)

We have 10" ducting to the outside with an inline 1000CFM fantech in the attic. I bought an 8" MUA vent with a vacuum sensor (which we installed in the ducting and ran to the basemenT) so we could add MUA, but the window has worked so well I am not going to bother...unles its unbearable in the summer when its hot muggy air I am sucking in.

I found this solution that looks interesting. https://www.hvacquick.com/products/residential/Makeup-Air/Residential-Makeup-Air-Fans/AirScape-Residential-Make-up-Air-Unit

it has an optional hot water coil - will have to talk with HVAC about connecting this to domestic water heater (NG) - would be more efficient then electric resistant. Maybe even tie a separate pump to it with fan interlock.

While oil heat is normally less expensive per BTU than electric heat, there are other considerations. Among these is the potential need to have the furnace send hot water to the hydronic MUA heating to keep it above freezing in the winter even when no MUA is being drawn.

Running plumbing to the MUA heater vs. running reasonably hefty conductors (in a cable or in conduit) has to be evaluated for complexity in the context of the house configuration. And the electric service has to be capable or upgraded. Similarly, the furnace power (BTUh) has to achieve the heating shown in my graph, plus perhaps whatever other zone needs one might not be able to live without, e.g., hot water heating.

My furnace configuration at the time of my kitchen reno was multiple Taco pumps -- one per zone -- including the MUA zone. (That zone used a heftier pump to achieve high flow at the head pressure from basement to attic.) Presently, a more efficient furnace is in use with zone valves, and all the zones operate using that single pump.

larson

2020 MMC code

501,2 states the entire 505 section is there to tell you HOW TO Construct a required makeup air system for a plus 400cfm hood,

MMC section 501.4.1 SHALL be determined... tells you if you need. by a positive or negitive vale at the bottom of the table

A quick skim of articles about the Minnesota Mechanical Code suggests that they have adopted a better than one-size-fits-all approach to determining MUA requirements, but of course it only applies in Minnesota.

In the context of MUA for serious cooking, my position is that even without combustion appliances one should provide enough MUA to match the hood system actual blower flow rate. This will maximize blower performance and avoid depending on house leakage which has its own set of deficiencies.

Just reporting back on my solution - HVAC contractor was very familiar with MUA - they recommended simple - I have an Elica island range hood with up to 1200 CFM blower and 8" duct to the outside (yes I know CFM vs duct size) - HVAC contractor installed the Broan motorized damper about 10' away in ceiling - So far all is working fine. The damper opens when the fan comes on (any speed) and I see good exhaust flow through the hood, and I have not felt any cold air drafts from the MUA.

As my house is foam insulated, the only leakage I would have otherwise is around ceiling boxes as the ceiling is not spray foam. My cooktop is induction and I wanted to reduce cooking orders with high CFM.

So far I am pleased with the results. I do have 10' ceilings in the kitchen, and that could be helping with comfort related to MUA. Cooking regularly in Ohio winter.

"HVAC contractor installed the Broan motorized damper about 10' away in ceiling - So far all is working fine."

This is against code in most of the U.S. And for very good reasons. A passive duct must have 3x-5x the duct size of a powered duct to function properly. 10" is not even close. This is why most codes require proper powered MUA for exhausting appliances over 400-600 CFM.

Do not count on closed cell to seal your house - it does not even with good installation (and people who've done research report that only about 10-20% of closed cell jobs are done correctly). What is your ACH50?

SO, you are very likely pulling air in through various leaks in your walls, around windows, doors and other things. That's not good.

It was irresponsible and ignorant of your HVAC person to install this.

I wanted to reduce cooking odors with high CFM.

High CFM will not do that. If it's not captured by the hood opening and then not contained within the hood until it can be removed then it will spread throughout the house.

That said, if you're happy with the results from an odor standpoint then it's working well enough for that. Whether it's effectively removing VOC's, Carcinogens and PM might be a different matter.

According to my HVAC contractor they install what they install because it does meet code. My foam is actually open cell - I am not saying foam is perfect, but it is certainly better than batt to seal openings. Ohio code is a little vague, and the motorized damper is the only requirement.

Since my last house had a 1200 CFM blower and no MUA, I am happy to be doing better than I was before.

I would have preferred powered MUA but I didn't want to dump it in the kitchen, and HVAC contractor indicated you can't dump it too far away or you could still wind up with negative pressure in the kitchen area and pulling in air from cracks and crevices.

And yes, High CFM alone is not the answer, but I do have the proper shaped hood, baffles and hood height that I met my requirements for odor.

I am also in a position to install powered MUA if needed. As my blower tends to only run on the first or second speed (out of 4) 99% of the time, I may not have to go that route. I need to do some air tests on my house, but haven't got there yet.

"I would have preferred powered MUA but I didn't want to dump it in the kitchen, and HVAC contractor indicated you can't dump it too far away or you could still wind up with negative pressure in the kitchen area and pulling in air from cracks and crevices."

You are currently bringing unconditioned air directly in to your kitchen? No filter? No heating in winter? No cooling or dehumidification in summer? And your HVAC contractor expressed concerns about an MUA that conditions the air before it enters the house?

MUA brought in to the duct system of a house (typically fed in to the return duct before the furnace) works well and is likely the most used system design. That said, best is if it enters as part of a hood curtain, next is near floor level from either side of the room but behind a cook standing at the range, 3rd is near the floor on the opposite side of the kitchen, 4th is duct system. Coming in to the ceiling is often not recommended because it will often 'short-circuit' and flow directly to the hood without taking any effluent with it (though if it's cold enough in winter it may sink down enough to work but you need about 3x the height in distance so 30' w/ a 10' ceiling.

As to meeting code. If that does meet code you've an exceptionally lax/antiquated code.

None of us has the flow rate needed to develop significant (fractional inches, w.c.) air pressure between rooms with open doorways.

I don't think an air curtain will be practical with residential equipment without generating turbulence at the plume zone, and cooling the cook.

If the MUA enters the kitchen at the location of the hood, it should be aimed across the room so it can approach the plume area as distributed low speed replacement air.

Replacement air will be high speed in the MUA duct but needs to be low speed in the kitchen. One shouldn't feel the draft. Try not to aim it at the cook's feet, or bounce it off of an island such that it reaches the plume zone still turbulent.

Hood system test kitchens use a perforated wall at some distance from the cooking appliance and hood to introduce MUA. You want to try to achieve some approximation of the resulting airflow within the limits of architecture and practical components.

"You are currently bringing unconditioned air directly in to your kitchen? No filter? No heating in winter? No cooling or dehumidification in summer?"

Yes, akin to opening a window. The energy required to heat incoming air in cold winter is extreme, and would not equal the temperature of air going out. And no one (that I found) makes a unit that cools or dehumidifies at all. The home HVAC unit is not designed for unconditioned air to be dumped directly in, so IMHO the passive air solution was the best way to start. I can always add a powered fan to my passive duct or relocate a powered fan to furnace room.

But I don't think unfiltered unconditioned air is the end of the world. We open and close doors all the time. Now if the industry made an energy/air exchanger to work with a range hood, I would have pushed for that. But since heated is the only current MUA solution, and I cook all year round, spending a lot of money and energy on a solution that doesn't work 100% of the time doesn't make sense to me.

Just curious, what do people do in hot humid climates with no winter?

Grease and entropy systems don't mix well so I don't know that we'll ever see an efficient energy exchanger. There are some collar systems where the incoming air is in a collar around the exhaust pipe but I think in general the cost/benefit of these isn't great and I'd assume they could also cool the exhaust air too quickly creating problems there.

Opening a window would probably be a much better solution than what you have now. It would lessen the amount of air pulled in through cracks and other places that you don't want it, your hood would work more efficiently (and likely quieter), and if you open one (or two or three) so that the air flows from behind you standing at the range then you'd likely get much better effluent removal.

You heat/cool/humidify/dehumidify the air no matter how it enters. It's more efficient and more comfortable to do it on entry and before distribution than to push it in to the room and do it through circulation.

Commercial kitchens will often have dedicated HVAC (heat/cool/humidify/dehumidfy) for MUA and then often dedicated ducts to distribute the MUA to exactly where they want it which is often in the far side of the dining area from the kitchen (and sometimes plus a little for a curtain system). Some residential will do this as well and especially if in a temporate enough climate that no conditioning is necessary.

Generally for residential the air is brought in to the return duct. The HVAC system (furnace, etc.) can deal with most outside air. If very cold then it can be heated. Typically an Electro Industries duct heater or MUA is used for this but it can also be hydronic if you have a boiler or solar system or geo if you believe the marketing hype. In our case we only heat the incoming air to +20°f for delivery to the furnace.

When we evaluate a direct passive (no blower) MUA system for acceptable pressure loss, one pressure loss that matters is that which allows a lot of air infiltration into the house though leaks. There is surely less infiltration with a duct of any reasonable size than with no duct. In fact, a duct might be as good as a partially opened window if the window still has a screen.

The other pressure loss that matters is dependent on whether there are combustion appliances. In some cases, -0.03 inches, w.c., is the limit on differential pressure, but in other cases we are only dealing with house leakage, and that should be determined ideally by testing. After all, there is always some house leakage during windy weather, no matter how we might address MUA.

I think that there are many areas of the USA where the codes allow passive MUA so long as the MUA duct diameter is at least equal to the hood duct diameter. Obviously, this doesn't yield zero differential pressure, inside to outside, as the hood system uses a blower. It may, however, yield a safe pressure depending on the type of combustion appliances in use, their possible alternative sources of local MUA, and their level of sealing.

"Just curious, what do people do in hot humid climates with no winter?"

Perfect passive MUA using traditional Samoan housing.

Air will always take the path of least resistance. So as the house depressurizes from the hood exhaust the first few CFM will likely come through the passive system. At some point it begins to become saturated (maybe around 100 CFM) and then other paths such as leaks in walls near various penetrations become lower resistance (relative to the passive that already has 100 CFM in it) until they begin to saturate a bit and then increasingly more is pulled through them and the passive duct until the internal vacuum is satisfied (approx equalibrium w/ outside).

Air, somewhat like electricity, takes all restrictive paths in inverse proportion to resistance. I would suggest a model where every leakage path, as well as the MUA path, has a monotonic non-linear quasi-parabolic pressure loss vs. flow rate with no saturation. There will be effectively a number of brown lines as on the figure below that, in concert, yield the overall pressure curve intersecting the fan curve. (Constructed by adding airflows at each element of a set of static pressures.)

In a normal open duct, saturation is not likely to occur until flow at some point in the duct becomes trans-sonic. This means that to first order, all leakages begin together and remain in some rough proportion. The exception will be if a damper is electrically operated when negative pressure has already been achieved or has high stiction when closed that must be overcome.

Dynamically, the speed at which the flow achieves balanced proportion depends a bit on distance traveled to the kitchen, but time to equilibrium will be fairly short due to the speed of air molecules at room temperature. The residence need not be modeled as an atmosphere of different air masses of differing water content contending with each other and gravity.

We have a 700CFM Zephyr hook and no make-up air in our 1000SF 1870s farm house which is about as drafty as they come. We have a strong bathroom fan too. Not sure what that CFM is but it sucks air around the window. We have lived like this for seven years are still alive :-)

We are adding a new similarly-sized attached dwelling which ought to be tighter, but not up to some people's standards as we just haven't got the budget or brainpower or available help to blower door test ourselves to tightness Nirvana, but will do our best. (We are in zone 5 hoping to insulate with caulked walls and mineral wool.)

The reality of life, our age (we are 60), inflation, and hard to find any help has us DIY'ing a lot more than we ever dreamed we'd need to do.

Our plan is to install a 630 CFM Broan 6" ducted hood direct-connected to their MD6TU make up air kit with a 6" pipe running 10' from the outer wall that is not heated, air conditioned, or humidity controlled. I'm reading up thread #opaone thinks this is a bad idea, which is devastating as we are without the luxury of time to research every last detail asa well as we'd like.

I've spent days trying to figure this out and had to make a decision two days ago before the Hardie lap siding when on yesterday. While that was happening I had to cut two 6" holes, made the mounitng block, flashed, etc., for both an exhaust and an in-coming line (with wall caps). Is this wrong?

I have read threads everywhere I can, and do not have plans to heat or cool via a ducted system because finding an HVAC contractor has been impossible. I can't even get my plumber to quote installing a water heater, let alone pipe anything (he is softening to the idea).

I am hoping to heat via a combi as we have one now, and supplement with a ductless mini-split at some point. I tried to reaearch HRVs, ERVs but these seem designed for whole house ventilation and not balanced make up air for hoods.

Knowing I might install a mini split, I found Fujitu ames a Fresh Air Kit for Large Caassette Units but the CFM is limited so not sure this would even work. This is very discouraging.

I tried to find hydronic (hot water heat) coils for the 6" duct but this isn't a solution, and doesn't deal with summer humidity. My last hope is to put the mini split unit near the MUP register. It's all very demoralizing for people who haven't unlimited time and resources isn't it!?

Well, it certainly takes a lot of time to filter through all the information and misinformation to conclude what is best for oneself. I decided to use my hydronic house heating system to also heat my MUA. An electric coil approach could also be used, but for my potential flow rates would have to be very powerful.

Heating and filtering devices do not have to match the duct size. My MUA duct path (when complete) will come from the roof to a blower, thence to a 4-inch filter caddy and the heat exchanger I have already installed. (At present the MUA is passively fed to the heat exchanger, which has a filter taped onto it.) The duct from the future blower will have to transition to the square filter caddy (2 ft x 2 ft).

I have no means of affecting humidity in my MUA path. I live in S. NH and I can tolerate the humidity having been raised in the Wash. DC suburbs without AC. So if some MUA usage briefly overpowers my split-cycle Mitsubishi AC, I can live with it.

Would you mind terribly sharing how you are using hot water to heat your MUA? This was what I had hoped to do. I read somewhere that to heat MUA unit that is balancing a 650 CFM hood you nneed a furnace big enough to cover a Bill Gates-type house. We have a crummy little 1200 feet here, and 200 of those are in an attic we doubt we will be able to afford to finish.

TI thought it was funny that you had posted that shot of the Somoan houses as our current house is balloon-framed and relies on wet/dry cycles for the wood to survive. It is 150 years old and the bones are strong, it leads like craxy but the big radiators keep us warm, and life doesn't seem so horrid :-)

Our new addition is our attempt at having a tighter envelope. I know ventilation is important, which is why I am trying to install a MUA supply, and if you're open to shairng your research on how to get this done with hot water heat I'd be very appreciative.

My personal belief is that since I don't have a back draft issue (gas furnace and water heater have their own air supply and/or power exhaust) anything I can do to provide make up air that is more automatic then opening a window is a bonus.

There is no solution I know of to condition hot humid air, and my climate is split heating and cooling equally. So for me it made no sense to spend a pile of money to heat incoming air, and then have no solution in the summer.

So I went for a passive solution. I know it is not equal to outgoing air, but so far it works fine. I hope to do a smoke test this weekend to get more data.

@John Answer text vaporized by Houzz for no apparent reason. Maybe I'll have time to rewrite it tomorrow.

I just want to add that I do understand what @kasekikaseki and @opaone are saying and I agree with most points regarding design of MUA systems (I read all the past posts here and elsewhere before making my decisions). But MUA requirements were initially designed for backdraft prevention and safety (CO, CO2, fire). If this requirement is removed (all electric or dedicated combustion air/exhaust) than the MUA discussion is all about comfort.

The comfort discussion requires taking into account climate and conditioning MUA to address climate. If it isn't possible to condition MUA completely (or at all) - is it worth an entire MUA system that does only part of the job - this is subjective.

The industry has fixated on kitchens too, no one seems to worry about MUA for bathrooms. Yes you could, but Heat/Energy exchanger systems can't handle this if more then one runs, and most MUA designs don't take this into account either. I have 100 CFM fans in my bathrooms (250 CFM in master) and laundry room - all on at one time could create 600+ CFM negative pressure (theoretically) - this isn't that far-fetched as 3 showers in a row and laundry room and powder rooms in use. But where would you dump makeup air to account for this? Yes powered MUA dumped in a central location, can work, but it doesn't appear to stop depressurization of the area immediately around the bath fans.

My point is that there is no solution that solves all problems. Even preheating entry air can only raise the temp of incoming air by X amount - it will never be close to room temperature on a day at or below freezing. And there is no residential solution that cools and dehumidifies air in the summer to room conditions. I really wanted to build a solution that could work in my climate, and cover kitchen and bath, but it didn't seem feasible from a cost and materials point of view and would not work well in all temperature/humidity conditions.

And I know my foamed home is very tight around walls, but I also know that the ceiling is blown in cellulose and I will get air leakage around most ceiling boxes - another point to consider even with powered MUA.

"I read somewhere that to heat MUA unit that is balancing a 650 CFM hood you nneed a furnace big enough to cover a Bill Gates-type house."

No idea where that came from but it's quite erroneous.

Best Electric Solution: https://electromn.com/make-up-air-2/

Fantech, Electro and others also make inline duct heaters for use with separate blowers.

If feeding the MUA in to the return duct then the air need only be heated to about 30-40°f as the house furnace will take care of the rest. If feeding directly then approx desired room temp.

IIRC for our 1200 CFM direct ducted in MN (planned for -34°f outdoor inlet) the gas furnace was going to be 52,000 btu/hr.

@Andrew M., Lack of proper MUA (from Bamasotan):

Not installing proper make up air carries numerous health risks including death.

• The highest risk is backdrafting of other gas appliances such as a furnace or water heater that are not sealed combustion.
• Backdrafting of a fireplace, even with no fire currently burning can cause substantial health risks.
• Moisture pulled in to wall cavities from outside can result in; mold in the walls which can be a very significant health risk for many people, the moisture can damage and rot the wall structure, and it reduces insulation value.
• Air pulled through leaks in wall systems reduces indoor air quality because whatever is in the walls gets pulled in to the house
• Poor hood performance from improper MUA will mean less VOCs, PM and Carcinogens exhausted and more spread throughout the house. A performance degradation of 80-90% is not unrealistic (think 120 CFM rather than 600 CFM). Make-Up Air is part of the static pressure calculation. If the blower has to pull air through leaks in the house that is a lot of additional static pressure.
• Increased hood noise as the blower must work harder.
• Shortened blower motor life.

While waiting a bit to get into the mood for more snow shoveling, let me address what wasn't included in @opaone's comments (in parts as a Houzz countermeasure).

Heat required: see chart. Use actual not blower rated CFM. Add in bathroom fan flows (corrected for pressure loss) if necessary.

On my hydronic heat exchanger:

I have an approximately 2 x 2 foot heat exchanger (looks like a 50s Chevy radiator) sold, I think, for people embracing nature living with wood boilers. It resides in an attic above a hallway ceiling. It has a known pressure loss (air-wise) that I have to take into account when I change from temporary passive to active MUA. It has a known 'head' loss to take into account when moving water thru it.

Two remote thermometers are used for hot water control One is between the exchanger and the diffuser in my hallway, and the other is stuck to a hot water return pipe next to the exchanger to detect any risk of freezing. The former is set to close a circuit at 65F, and the latter at (IIRC) about 40F.

Thermometers are wired in an OR fashion as if the combination was a single wall thermostat controlling one zone of my presently 8 zone heating system. I use a larger sized than usual Taco pump to achieve the head and flow rate of the MUA exchanger as well as long loops into a house addition. (Water pumps have the counterpart of a fan curve that has to be accounted for.)

On multiple blower MUA control:

I have two kitchen exhaust blowers, three bathroom fans, and a rarely used fireplace. One or more windows may or may not be open. My solution, partly implemented back in ca. 2010 when I started being pulled from that aspect of my kitchen reno, was to control the MUA blower based on the differential pressure between the kitchen and the outside (represented by a pressure feed from a well ventilated attic). The motor control would be by current loop from a Fuji control processor. Due to the number of poles (lags) in such a system, the motor control has to implement a stable closed loop control system. TBD

My only combustion appliance is a oil fired boiler with its own MUA and sealed exhaust, so the house pressure can be as low as a passive system will make it without causing any safety hazard. Of course, the blower flow rates will be lower than with a properly balanced system as I hope to get to finish one day.

Note that this air pressure control loop is independent of the thermometer control loop that keeps the heat exchanger from getting too cold or not heating the air sufficiently as measured just below it.

Thanks, kaseki, for the graph and explanation. I know how frustrating the loss of a post can be, and in reading your replies, the thought going into same by you, and others here, is considerable. I have to to say most of what you, and others, have written is 'over my head' insofar as how it all relates to implementing a simple, affordable, DIY MUA solution (at my neophite level) is concerned :-). You must be an engineer or something. You are way smarter than me! Sure seems like there's a gap in the market for a simple solution....

"I read somewhere that to heat MUA unit that is balancing a 650 CFM hood you nneed a furnace big enough to cover a Bill Gates-type house."

No idea where that came from but it's quite erroneous

Hi opaone, yes I made a typo: it should have been 900 CFM not 600 CFM. I was just trying to make the point that it had been noted we need to have a lot of heat to warm the make up air, and I don't know how to get this done without having some massive framing work and pllumbing and electrical too. I believe I got that from a post up thread from kaseki about four years ago.

He wrote: "For example, 900 CFM is 54,000 CF/hr being raised as much as 50 degrees (more in N. Minnesota). This would be equivalent to a house volume (assuming no leakage) of 270k cu. ft. being heated 10 degrees per hour. A 27,000 square foot house with 10 ft ceilings would be of this volume. Lacking a Bill Gates' house sized furnace, you may need supplemental heating."

Now, your link to Electro's electric MUA heater is really interesting. I had seen Fantech not this. Both big and costly! The daily use cost is what I wonder about, and I don't see any reviews (at least not at supplyhouse.com). Of course, operating these varies based on one's power needs/costs, and where I live electricty it not cheap. I am incapable of calculating what my daily use cost might be, using the Electro model MD-10 as an example (designed for 600 CFM fans), the specs are beyond my skill level to assess a cost to run the thing.

I do see that unit has a 10" duct, and puts out around 34K BTUs of heat, which is about what I was planning to use to heat the additon in its entirety.

Heating a house in my area, using electricity, is not considered the best option as I looked at an electric combi boiler and was reading comments and this was pooh poohed....

You did a good job of explaining the best- to worst-case examples of brining in the MUA, and of course like an idiot I cut a nice big fat 6" hole in my rim joist so I could bring the air into the middle of the LR/kitchen via the ceiling, which was the worst option you very intelligently noted.

I learned a little about air flow reading a paper from the dept of energy website where they talked about throw and how the air hugs the walls, etc. Balanced vs supply vs exhaust vs ERV/HRV and how all of that relates to this thread makes the whole topic in general complex for the layperson, and as mentioned previously: good affordable help these days is... hard to find.

These types of threads and forums are all most of us have! Thank you for your valuable contribtions.

1 BTUh = 0.3 W, or 1k BTUh = 0.3 kW, or 60k BTUh = 18 kW, or 75A @ 240 Vac.

The point of the large house was that its furnace is not normally designed to heat a large flow of cold air; it is only intended to compensate for heat loss and warm rooms at a modest rate.

MUA should, for typical residential use, only operate at full power for brief periods, and partial power for longer periods. Assume full power for 10 minutes, and maybe 20% power for an hour. So for a 60k BTUh example requiring 18 kW for high CFM or high differential temperature, usage would be 18 kWh x 1/6 hr + 18 kWh x 0.2 x 1 hr = 6.6 kWh. At 20 cents per kWh, the cost would be $1.32, plus whatever power is used by the MUA blower, if any.

When the meal is based on heating soup, the MUA might be zero, so this cost is intermittent in many cases. MUA heating capability is based on worst case, but heating required depends on the weather and what is cooked.

Compare to the prorated per-meal cost of money and depreciating capital invested in a kitchen renovation.

kaseki... where were you when I was in junior high school, high school, college, and adult life lol?!? You $.20 is very close to what I am paying. When I last checked, it was about $.22. So while burning a hamburger, as I often do, I'm looking at a buck thirty five or so a crack, ~$1.35 per 'event', is that about right?

Now, we have 100 amp service in our house, and are looking at a gas range since we are already pushing our power envelope as it is. (Upgrading to 200 for us is not easy, and very costly.) We wanted induction, and are having to go gas bc of the power limit ('ve run a 6 awg wire to a box anyway, and have a 50 amp circuit breaker in the panel should we ever find a way to upgrade...).

Is this thing really the best way to go, and if I used it, would using an adapter to take the 10' pipe fitting on the unit down to 6" which is what my limit is for the rim joist ruin it's operating capacity?

(Am I hijacking this thread? I don't mean to be!)

This whole thing has be wondering if I ought to seal the hole, leave the wall cap as is since it is already sided now (around the mounting block), and somehow duct real 10" pipe in a chase to/from the attic or the crawlspace. My hope is to condition the crawlspace. I have two 6" pipes in there now. I have only a vent for the main stack on our new pressure treated cedar shingle roof, and two vent caps for the roof in my car: one 4" and another 7" (biggest I can find around here).

The OP wanted to simply solve where to put his air source, and this is obviously very complicated, and really ties into everything in some ways eh kaseki?

"Dumping air into a basement where it is electrically heated during high flow periods can work, but will depend on whether this area is free of fumes from home projects...." was what you had written at the time this thread was started. If I mix cold and warm air in my crawlspace, then flow that up into the kitch for MUA, is there a problem in zone 5 during the summer when I start pumping in that hot muggy summer air? I assume so.

The false notion that this is simple for the nob is discouraging. It makes me really question the wisdom behing tight houses in general, as we've lived in drafty balloon-framed, uninsulated, unsheathed (3/4" cedar lap siding over rosin paper and lath and plaster) for seven years and never needed to worry about any of this!

I had this fantasy that a couple of cheap Panasonic ERVs were going to solve all of the whole house woes. How woefully wrong I was.....

To further was @kaseki was saying... Here's energy use for our Electro MUA that ran while I made porridge this morning. It was +8°f outside, running at 600 CFM, heating to 40°f.

"So while burning a hamburger, as I often do, I'm looking at a buck thirty five or so a crack, ~$1.35 per 'event', is that about right?" You are saving the house from grease condensation and perhaps your respiratory system for $1.35 or whatever.

I don't think pulling in muggy air for a short time is too much of a house hazard if you have A/C to dry it out in reasonable time. Without A/C, it would be muggy anyway.

"The OP wanted to simply solve where to put his air source, and this is obviously very complicated, and really ties into everything in some ways eh kaseki?" Ayuh.

If you don't have any combustion appliances taking air from where your kitchen is, then a passive system (with heating and filter) can be sufficient. Try to minimize pressure losses beyond those of the filter. Furnace filter, or perhaps even a window screen can be used for filtering.

Does the Electro power on and off per the spikes in your graph opaone? Can I borrow your higher IQ to tell me the net total eltricity burn for the porridge event?

kaseki "I don't think pulling in muggy air for a short time is too much of a house hazard if you have A/C to dry it out in reasonable time. Without A/C, it would be muggy anyway."

Yessir. I was considering using the crawlspace as an entr point for the MUA. Option B would be the attic 2.5 stories above grade. If I were t implement the Electro would it be better to have MUA come in via the basement or the attic?

If I read opaone correctly: "the best is if it enters as part of a hood curtain, next is near floor level from either side of the room but behind a cook standing at the range..."

So, the crawlspace is directly below is MUA entering the house through there better than the attic? I have no idea how to introduce a 10" vent into the "hood curtain" opaone! Have you ever done this yourself, or is there some place I can see an example?

kaseki: "You are saving the house from grease condensation and perhaps your respiratory system for $1.35 or whatever."

Is why I am here :-) I have a Zephyr sucking a lot of CFMs right now. I have no idea maybe 700. I do not have mold or dirt lines in perimeters of our current house as this place is 150 years old and very drafty, whcih we actually like. It is the new place we are tryig to do this for, and I agree the $50/month or more for just heating the air a little bit before it comes in is worth the coinage if that's my ventilation tax! (Not a political statement :-)

"If you don't have any combustion appliances taking air from where your kitchen is..."

I do! I have a gas range/oven. Is that a "combustion" appliance? Do I need to worry about this?

Down, adjacent/attached to the crawlspace, will be a mecahnical room with no door between it and the crawlsapce. In there I hope to have a gas combi boiler. This is due to the cost of gas heating still being practical for our area, and the limited power I have. This appliance is partly what has me wanting to be sure I avoid negative air pressure.

Replace "combustion appliance" with "back-draft sensitive warm exhaust combustion appliance. Ranges don't apply; modern gas furnaces do apply. If you put in the furnace so that it has its own MUA and sealed exhaust, then it shouldn't be susceptible to back-drafting. See installation guide.

Every house is different and the MUA approach has to take that into account.

I think opaone's air curtain is a specific scheme for commercial hood systems that does not apply to residential hoods.

Introduce MUA at the ceiling so that it flows away from the hood if inserted near the hood, or flows toward the hood if relatively distant (10s of feet). Alternatively, use a number of toe kick areas to spread the flow from the floor area, but keep the flow away from immediately rising where the cook it. Either way, you want the MUA to approach the cooking area in a relatively non-turbulent manner. Depending on how you do this, you want to either use registers (not very directional) or diffusers (directional) where the MUA enters a room. Hart & Cooley (or vice versa) have a bazillion options.

I'm unclear about your choices of MUA path. Generally you either duct the MUA to where you can condition it and then send it on to a specific distribution point somewhere near the kitchen, or you release it in a room you can heat that connects to the kitchen but doesn't add dust or odor to the flow. Roof mounted systems are common for commercial enterprises. The roof can get one into cleaner air, but care must be taken to get air that doesn't include the cooking effluent or furnace exhaust. Naturally, if floor entry is easiest to implement, then MUA intake will be near the ground unless the entry duct goes up a ways. Try for the simplest scheme that you think will work. Providing separate MUA for combustion appliances allows much simpler schemes, in general, but heating is still needed for cold environments.