3 bathrooms in a 900 sf house? Typo? Because get leave no actual real living space.

Thanks, @User. The house is 22'x45'. There is a master bathroom and a guest bathroom on the main level and a half bathroom in the basement.

I'm not sure about the woodstove. When I did mine, a separate passive fresh air source was required for combustion. Nowadays, there are systems that get combustion air from the flue pipe (multi-layers). Some use a 3" pipe through the wall or back of the firebox.

Thanks, Kaseki!

There are requirements set by international codes often adopted by the local code authority (might be the state) and there are goals.

Understood.

Goals first. Goal 1 is to not backdraft combustion appliances and possibly introduce carbon monoxide into the house.

Agreed. Fortunately, this house's furnace (Carrier Infinity propane furnace/heat pump) is direct vent/sealed MUA, water heater is heat pump, cooktop is induction and oven and dryer are electric - leaving only the woodstove as a safety concern, I believe.

Goal 2 is to not gag the blowers in use, particularly the kitchen ventilation. Hence the need for make-up air.

If it's worth doing, it's worth doing well.

Most inspectors will want an MUA system that conforms to code, but they don't generally quibble about how effective it actually is, as far as I have heard. In other words, they don't measure internal vs. external pressure vs. what type of combustion appliances (without their own MUA) may be present, or which may be present in the future, vs. what fans and blowers and fire places are operational. In fact, the code only addresses kitchen ventilation above a particular flow rate, and ignores everything else in the house. It also ignores whether the house is leaky or tight.

Right. I want to do what's best, not just what's required by code.

So what is good enough? In the case of passive MUA (no blower), there may be pressure losses in filters and heat exchangers (when present). These may be tolerable for hood function and appliance safety. This leads to a fairly simple MUA. It is particularly applicable when the combustion appliances use their own MUA ducts thereby avoiding the safety issue, and leaving mainly poor fireplace draft as an issue.

I've read that passive air inlets usually don't work?

https://www.greenbuildingadvisor.com/article/passive-air-inlets-usually-dont-work

In the case of active MUA (with blower), over pressure could occur if some control is not present. So the degree of refinement of the actual achieved house pressure (pressure balance) is somewhat up to the owner.

You are just saying that active MUA needs to be controlled? Examples could be by a pressure sensor or by matching the volume of air exhausted as in the Fantech MUAS.

In the case of the kitchen ventilation, the pressure loss in the MUA system translates to a volumetric flow rate loss in the hood blower.

I'm not sure what you mean here.

How much depends on the fan curve of the blower, and for Broan, these are usually available.

The only reference to "fan curve" I could find with a quick Google search of BROAN was: "...how many elbows you are planning to use and we will do a fan curve for you."

In my house, with both 1500 rated hood blower and auxiliary kitchen vent blower (data lost, maybe 600 CFM), multiple bath fans and fireplace, I choose to design for pressure-based control, even though I have sealed MUA for my furnace and have found by recent air velocity measurement that my kitchen hood is achieving greater flow rate than I expected.
In your house, the actual flow rate of all the fans in use together with the windows and doors open is likely to be well under 1000 CFM.

You are basing this on a rough estimate of my volumetric flow rate loss?

The effect of pressure on the wood stove draft is unknown to me, but may be available from the manufacturer.

I have spoken to the inventor of the woodstove. Anytime I mention needing makeup air for the house because it's so tight, he repeats his stance that he is vehemently against providing outside air directly to the woodstove unless required by code or insurance. When I ask if I should be concerned about the woodstove back-drafting in such a tight house, he repeats that if it does - providing outside air directly to the wood stove isn't the solution. This isn't really what I am suggesting. I was just trying to find out if providing makeup air to the house in the amount that the wood stove would be exhausting (Cfm 125 at top and 75 normal run) would help eliminate back-drafting. So, you are suggesting I inquire about the effect of pressure on the woodstove draft?

With respect to the referenced MUA system. Unless you live in an area where heated MUA is a local requirement, this unit seems applicable, albeit possibly overkill for your actual air flows.

Anything worth doing is worth overdoing, ha ha.

I notice that a heater is also available, but note that some (heh) plumbing will be needed, along with controls to not only try to keep the air warm, but also keep the plumbing/heat exchanger from freezing when no MUA is needed.

This concerned me, so I contacted Airscape. They told me heat was also available by "strip heat". I would prefer electric heating, so asked for a recommendation of an appropriate unit to be used in conjunction but was only told "an inline coil filter that runs independently from a duct stat" could be used.I searched on my own and found some MUA heaters: https://www.ecomfort.com/fan/make-up-air-heaters.html. I have no idea how to select the correct one.

Noise levels do not seem to be addressed. A Fantech silencer might be desirable, or at least planning for one in establishing the mounting location.

Noted. I hadn't considered this, thank you.

This unit requires both entry and exit interfaces with the house. Cost seems reasonable, but exact extent of what is included on the spec's page suggests that there will be some added elements needed.

I thought the price seemed reasonable despite the exclusion of some elements. The Fantech solution is in the same price range and only addresses the kitchen exhaust issue, from my understanding? One element I wondered about - a damper at the intake that opens only when the unit is activated?

Other topics: One big issue is how the air is going to get introduced to the kitchen without causing a draft at the kitchen hood(s).

This is among my follow-up questions. Where should the air get introduced into the kitchen? High? Low? I read a BSC article suggesting it should be both and at different percentages. Should the MUAS have it's own ducts and vents or can the air be introduced through the HVAC supply or return as I've seen suggested? I assume there should be a MUAS grille near the woodstove? One near the dryer? MUAS grilles in the bathrooms?

Another is where the intake on the roof (or somewhere else) will be in relation to prevailing winds and hood/chimney exhausts.

Yes. Important considerations.

Is there room in the attic?

Yes, but if it is okay to use the existing hvac ducting or if low introduction ideal can it be installed in the basement mechanical room?

Do you need heated MUA?

We are in central Pennsylvania. My thought was that I should since the house is smaller and we would be moving a relatively large amount of air. You don't think we will be exchanging a considerable amount of air? Also, why do I not see anything about cooling MUA during warmer months?

Will the requirements of this extract of another Appliance forum member's message be met?
Bottom line: this is a fairly turnkey device that should be sufficient, airflow-wise. 3 pa sensitivity (if I read the spec right) should be sufficient.

You are saying the Airscape MUAS reacts to pressure changes as low as 3pa and this is right at the line of what we would need?

No doubt there are myriad ways of sensing pressure. There are myriad ways of building MUA systems.

Ah, but how many are there for someone like me who knows nothing about any of this, ha ha. "Fairly turnkey" is the key phrase I think you used.

Fantech sells one, for example.

Is Fantech's one not just for the kitchen exhaust?

Another question - will a MUAS interfere with the ERV system?

Thanks, @weedmeister. As you can see from my comments above, the inventor of this woodstove is against outside air. He doesn't seem to think MUA is necessary for the woodstove or maybe I haven't been clear about what I am asking him about.

Responses in parts

I've read that passive air inlets usually don't work?

https://www.greenbuildingadvisor.com/article/passive-air-inlets-usually-dont-work

That discourse is not applicable. First, one uses a damper, maybe electrically actuated to keep out air leaks when the interior pressure is not low. Second, the duct has to be larger for any significant MUA level.

In the case of the kitchen ventilation, the pressure loss in the MUA system translates to a volumetric flow rate loss in the hood blower.

I'm not sure what you mean here.

I mean that pressure loss in the MUA system is part of the pressure loss in the ventilation system [stove top to outside to inside to stove top] and increases in MUA pressure loss lead to decreases in the achieved volumetric flow rate (CFM) of the hood ventilation per the blower's fan curve.

The only reference to "fan curve" I could find with a quick Google search of BROAN was: "...how many elbows you are planning to use and we will do a fan curve for you." Concept and random example below. I consider the fan curve to be the black line and the pressure loss curve to be the red line. [Click on Houzz images to magnify them.]

You are basing this on a rough estimate of my volumetric flow rate loss?

Yes. I usually assume 2/3 of rated zero static pressure flow rate. But in actuality, it will depend on house leakage and what fans are on or off and baffles vs. (partially dirty) mesh filters, duct sizes, etc."

Anytime I mention needing makeup air for the house because it's so tight, he repeats his stance that he is vehemently against providing outside air directly to the woodstove unless required by code or insurance. When I ask if I should be concerned about the woodstove back-drafting in such a tight house, he repeats that if it does - providing outside air directly to the wood stove isn't the solution.

But really, all the air that gets to the wood stove was initially outside air.

... So, you are suggesting I inquire about the effect of pressure on the woodstove draft?"

I think I would suggest that he doesn't know the draft vs. inside/outside differential pressure. It might not be easy to measure, and would likely depend on how hot the fire was, or how much wood was combusting, stack height, and how tightly the stove was sealed. Because a choked wood stove is different from a wide open fireplace, it might tolerate more pressure loss than a fireplace.

Anything worth doing is worth overdoing, ha ha.

Yes. My father used to tell me as a kid that anything worth doing was worth doing well. Later I decided the adjective "well" should be "in excess."

I searched on my own and found some MUA heaters: https://www.ecomfort.com/fan/make-up-air-heaters.html. I have no idea how to select the correct one.

This may help.

Divide by 3.4 to convert BTUh to watts. Use the estimated actual flow rate, not the sum of all fan rated flow rates.

One element I wondered about - a damper at the intake that opens only when the unit is activated?

Intakes should be screened and dampered.

Where should the air get introduced into the kitchen? High? Low? I read a BSC article suggesting it should be both and at different percentages. Should the MUAS have it's own ducts and vents or can the air be introduced through the HVAC supply or return as I've seen suggested? I assume there should be a MUAS grille near the woodstove? One near the dryer? MUAS grilles in the bathrooms?

Air should be introduced to become relatively laminar at the hood, so a ceiling diffuser aimed away from the hood, or a diffuser down a hallway, or a lot of toe kick area not at the cook's position may work.

I can't answer about using the HVAC system, but it might not like being so used. I would supply to the kitchen. Air can flow to other places if not sealed off, and in the case of bathrooms, sealing off cuts the fan flow and in any case isolates the pressure loss. Only if you need (due to a tight door) MUA into the room would you add another duct exit. I don't know your house architecture, so you need to determine just what can be where. The drafts in the hallways to these smaller exhausts should be relatively tiny.

Yes, but if it is okay to use the existing hvac ducting or if low introduction ideal can it be installed in the basement mechanical room?

Anywhere is fine, but the air intake needs to be where it is free from other odors

You are saying the Airscape MUAS reacts to pressure changes as low as 3pa and this is right at the line of what we would need?

I think I would prefer to say: If the Airscape reacts at 3 pa, then I have read their spec correctly (the wording seemed to not be what I expected), and that it should be good enough (+/- your woodstove). I'm not sure that a unit that has to control up to 1700 CFM should be expected to control well down to a few hundred CFM with less than 3 pa differential.

Is Fantech's one not just for the kitchen exhaust?

I haven't studied Fantech's control system so I don't know.

Another question - will a MUAS interfere with the ERV system?

I don't have an ERV system, but as I understand them, they move heat from deliberately exhausted air to deliberately induced air. The MUA keeping the house pressure close to the outside pressure should make the ERV performance more predictable.

Thanks, @kaseki!

Could you tell me where you would place the MUAS vent(s) based on the attached layouts?

Could you recommend a MUAS heater?

You need a kitchen layout diagram. Is the lower plan for a basement? If so, what is all the stuff below the kitchen? Where are the room doors located in both floors?

Generally, if I didn't mention it above, you want to introduce the make-up air so that it is relatively non turbulent when it gets to the hood/cooktop.

I can't help with a suggested heater. You need to know whether hot-water (hydronic) is applicable or electric is better suited to the space and installation issues. Didn't your choice of Airscape allow for an electrical heater module to be included? The Airscape could potentially be located in a basement so long as decent outdoor air is available. The difference is whether the interface with the kitchen air is via ceiling diffusers and registers, or floor registers and/or maybe toe-kick registers. Placement of MUA parts, even in a new house, is difficult due to the many other household features not generally an issue in a commercial kitchen.

There is a house in Exeter NH next to the river that when I was last there appeared to be under re-construction to be a restaurant. One could see on one side of the house large ducts come out of a wall and go up to the roof area to provide for MUA and exhaust. In other words, for residential configurations, nearly every instance will differ from others, usually driven by internal features.

The first diagram is the main floor showing the hvac grille placement.

The second diagram is the main floor showing the location of the exhaust fans, the wood stove, and the dryer.

All the doors are shown on the second diagram - they are pocket doors.

Below is a more detailed diagram of the kitchen.

I'd prefer electric MUAS heat.

Airscape has a hydronic MUAS unit available, but they told me heat was also available by "strip heat". I asked for a recommendation of an appropriate unit to be used in conjunction but was only told "an inline coil filter that runs independently from a duct stat" could be used.

The Airscape could potentially be located in a basement so long as decent outdoor air is available. The difference is whether the interface with the kitchen air is via ceiling diffusers and registers, or floor registers and/or maybe toe-kick registers.

If you could recommend placement for both scenarios and let me know which you consider most ideal, I can work it in.

Kitchen diagram missing. Stairs go to the basement, I presume. Is there attic space?

If the kitchen has a door that can be closed, then the MUA must be fed to the kitchen. Feed to the DR/LR could be supplementary. Feed to baths would only be needed if the doors seal and you want actual flow from the bath fans.

Insight into mounting locations is very site dependent. My general preference would be a ceiling diffuser aimed away from the hood (maybe aimed away in three directions). See Hart & Cooley catalog for examples. Also, in the case of the Airscape that has an intake duct into the house, that too would have to connect to the kitchen and anywhere else that the unit supplied MUA. Did I mention site dependence?

NOTE: I am not a HVAC engineer. I am a systems engineer who is concerned (on this forum) with hood and MUA performance requirements. I can't see from here all of the house details that can influence where machinery and ducts can best be positioned.

Kitchen diagram added.

Yes, stairs go to the basement.

Yes, there is attic space.

The kitchen does not have a door that can be closed.

I realize this is all site-dependent, but without knowing the ideal position, I can't begin working around the prohibitive house details.

Ideal is emitting MUA from a perforated wall distant from the hood. This is how hoods are tested for spillage as a function of flow rate. Not even a cook is present to disrupt the flow field.

Everything we are likely to achieve with MUA in a residential setting will be less than ideal. Quite a few approaches will probably be (as far as I can see, at least) equally good enough. Supplying the MUA (assuming it is heated when necessary) into the living room via a ceiling diffuser should remove most turbulence by the time it reaches the kitchen. This should be better than, say, emitting the MUA at the cook's feet where the paths to the hood add turbulence to that existing at the toe kick and are not temporally consistent. It should also be better than emitting it into the dining room where a breeze might not be appreciated over the food, even though the air is filtered.

My MUA is inserted via a 3 x 3 diffuser into a hallway (3 feet wide) where it flows to the kitchen and LR. The breeze is very slight when expanded into a 24 square foot sectional area.

So, given the attic availability, the general desirability of taking the MUA from the roof (appropriately distant and upwind from the hood air exit point and wood stove chimney), and the possible ease of choosing a mutually convenient LR ceiling location and corresponding attic location for the diffuser would lead me to selecting an attic location. This also reduces the amount of space taken up in the basement which might be put to other uses.

Depending on the LR layout and usage, I would pick a ceiling location that is not too obtrusive and if not maximally distant from the kitchen, then at least farther away than halfway to the most distant point. Plan LR lighting first.

We don't know how much vibration the MUAS might induce into the house structure, or add to the duct noise, so system mounting off of the attic floor joists might be called for, or some dampening pads could be used under the unit.

Besides the roof input to the MUAS, and the ceiling exit from the MUAS, the Airscape also uses an intake from the interior. I don't know if that is actually needed, or whether it is a convenience for locally measuring pressure drop. In any case, I would either connect it to the ceiling near the wood stove, or inside the kitchen. This may not matter much at these airflows, because the pressure difference between open parts of the house is likely to be extremely slight.

On the subject of MUA heating. For electrical heating, one wants a thermostat control for power, and a set of coils in the airflow. Greenheck builds such devices for their commercial MUA systems. Electric clothes driers have these also. A former(?) forum participant @cooksnsews had one in this MUA path. (See aluminum box in image; the blower is the white section.) I don't recall him reporting where he got it, however. Photo link is http://ths.gardenweb.com/forums/load/appl/msg0711051415510.html. How much electrical power you will need can be estimated from the graph I earlier presented in this thread.

Addendum: Older cooksnsews threads seem to be "not getable." However, I found a thread where @weedmeister noted that one can get duct heaters for a low price. Perhaps he will elaborate. I don't have time to search for them at the moment.

To OP: did you end up getting the Airscape MUA? We're remodeling our kitchen are are diving deep into the MUA world (something i didn't even know was a thing until my wife decided she wanted a gas cooktop). We're looking at the Fantech MUA kit, but the Airscape unit seems to have more intuitive control. Your thoughts are greatly appreciated!

Sorry for the delayed response, D B. We are still considering it. I will check back with any new information. Please let me know if move forward with any plans in the meantime.

Also looking for some real world experience with the Airscape...

Reading this thread with interest. Wondering if anyone has experience with the AirScape MUAS. I had intended to use the Fantech MUA system, but my remodel has taken an extra year, and I recently learned that Fantech discontinued the 1600 and 2000 MUAS in September 2022. I took an overkill approach with my range hood and got the Trade-wind 7254, which has dual 10" ducts to which I was planning to attach Fantech RE or REC 10XLT (1080 CFM per roof fan). I have a 48" all-gas Wolf with 4 burners and integrated the griddle, so I don't absolutely need 2000 CFM. However, I do wok cooking and occasional frying of bacon and fish, which create smoke and smells I want to get rid of VERY efficiently.

Has anyone committed to a system and can share their experience?

• @nexp I did not buy the AirScape. I ended up with a MUA system put together by HVACquick.com - https://www.hvacquick.com/products/residential/Makeup-Air/Residential-Makeup-Air-Fans/HVACQuick-Ruck-Balanced-Residential-Make-up-Air-System Then, we added an ERV on the bedroom side of the house and balanced the air to offset 110 CFM bathroom fans and the dryer.

Interesting - I hadn’t seen that product. I just ordered the airscape from them. I figured the pressure activated control would be useful for addressing the gas dryer and open fireplace, and I particularly liked the hot water coil and built-in control. Around here, heating the make-up air by gas-fired hot water is much cheaper than electric resistance. I haven’t found anything on the internet from anyone who actually bought one - just people who have considered it.

With your Ruck system, the vent hood and the make up air both use the same model of blower?

Nexp, did you install your airscape unit yet? If so, how do you like it? Is it loud?

We are considering one of these but similar to you can’t find any input from anyone who actually owns one!

I think @opaone's MUA system is described here: https://bamasotan.us/range-exhaust-hood-faq/

Does he have an airscape? I didn't think so but now am wondering...

Accurex, I think, but the control system is by someone else. I'm sure the details are addressed in one of (or a few of) the main kitchen ventilation FAQs or at his bamasotan website.

@John H I actually have not installed it yet - we have a rather unique house - the kitchen is in what is techinally walk out basement, and the only utility space is a sub-basement/crawl-space under the kitchen, which muse house a water heater, ejector tank, ERV and the range-hood ducting. Thus, the HVAC contractor does not think it will physically fit, along with the difficulty of fitting sufficent supply diffusers from under the floor. I’ll be sure to report back if we do get it installed!