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Air Tight house make up air ventilation system.

Andrew M
3 months ago

Hey guys,
I'm building a tight house (full envelope and passive standard but will not certify). In a climate that is 85 in the summer and 20 in the winter.
The house has an open layout with very high ceilings. The living room/ kitchen area is around 1200 Sq. Feet with ceiling height around 15 feet at the peak in the kitchen and 25 feet at the peak in the living room.
Ive spent quite a bit of money to make an envelope of airtightness and don't want to mess it up. We do have a chimney insert, but the air will be drawn from the exterior and the whole insert will be inside an insulated and airtight box.
So down to the issue:
My kitchen will have a 48" gas range with around 90000 btu. Though it's highly doubtful that I'll use all at once, I do want to prepare for it.
So will be getting a 900 cfm range hood to go along with it.
Now my idea is to have the extracted hooked up to a berbel wall box to maintain air-tightness.
https://www.berbel.uk/extractor-hoods/accessories/exhaust-accessories/wall-box/
The idea is to put in-line with the ventilation hood electrical so it opens whenever the hood is on.
As for the Make up air, my idea is to install a Canadian well (will already have 1 for the hvac system). This should normllalize the air temperature that enters the house. If it's 35 degrees out, the air should enter at 55-60 based on my calculations.
The Canadian well ventilation will enter into the house, the idea being that it warms or cools the air during the respective season.
Once the air enters, it will pass through a an electrical resistance duct heater in line with the same electrical as the vent hood. Will install an on-off switch as well to turn it off in the summer or whenever it's not wanted / needed.
After this, the duct will continue and I plan to put another berbel exhaust flue or similar (also in line with hood extractor electricity) Not sure if a fan is needed at this point or it will be sufficient to have passive airflow as needed.
I suppose since the seal will be after the ducting enters the house, I will need to insulate the duct on the interior. Alternatively I could find an airtight flue that goes in line with the ducting and place it at the barrier between exterior/interior.. In case someone knows of a product like that let me know.
In any case, I think in this way I'll be able to put relatively warm make up air in the house during the winter.
What are your guys' thoughts? Should I add a pressure sensor to the system? Or just have it automatically activate with the hood? Does it seem viable? I'm not an arquitect or builder.
Any ideas to modify or improve this assembly?
Thanks!

Comments (26)

  • darbuka
    3 months ago

    I’m hoping @kaseki sees this. He and @opaone, are the ventilation experts on this forum.

    Be forewarned…certain people reading your post, particularly one pro who runs a catering business from her home, will likely tell you that ”no one needs a 48” range”…often with the qualifier ”unless you’ve got 10 kids, and are cooking three meals daily.” Preparing you for the inevitable.

    Andrew M thanked darbuka
  • aklogcabin
    3 months ago

    I live in AK and building a tightly sealed house. I am going to add a 2" abs pipe into an outside wall. We also have a 14' tall cieling with a cacederial truss. The bottom of the pipe will face outside and the top inside. And I will install an in line fan with in case foul odors from cooking n such need to be exhausted outside. This will allow me to have a passive or forced air fresh air intake. With heat stacking in the pipe, it will insure that cold air is not entering in the house. But when air is removed there is always fresh air coming in. Such as when a stove hood fan is running.

    I'm concerned that I may build too tight and want to insure that I have fresh air available. This will also balance the interior air pressure and insure a positive air pressure so that the air space is changed out.

    Good you are thinking about the interior air and how to insure that you always have a good air flow to exhaust odors or air borne germs that can cause colds n such. And your home will have fresh air at all times while it is sealed tightly where needed.

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  • opaone
    3 months ago
    last modified: 3 months ago

    For a passive house you generally want all balanced ventilation. So whatever your range hood is exhausting you'll want to bring in that exact amount w/ MUA. If the range hood is on low and exhausting 400 CFM then you want your MUA to be bringing in 400 CFM.

    Keep in mind that consumer range hoods often deliver about half the advertised CFM.

    Your duct heater should be temp based (thermostat) not switch based. It should provide whatever heat is necesssary to raise the incoming air temp to your desired outlet temp.

    Do some research on canadian wells. When we looked at it (in MN) I think we came up with something like a 15 year payback period. Somewhat better than heat pump geothermal but not great. Installation is expensive, the fans use a lot of electricity due to the high static pressure, and it is not maintenance free. I think they're a great idea but not sure how practical.

    More here: https://bamasotan.us/range-exhaust-hood-faq/

    Andrew M thanked opaone
  • opaone
    3 months ago
    last modified: 3 months ago

    "Once the air enters, it will pass through a an electrical resistance duct heater in line with the same electrical as the vent hood."

    What do you mean here by inline? These ducts should be completely separate.

    Do you mean that the MUA fan is interlocked with the range hood so that it comes on anytime the range hood does?

  • opaone
    3 months ago

    As to pressure... Using pressure sensors is tricky since the pressure is different on different sides of the house. You realistically need differential pressure sensors on each side with the exterior a T pipe and then average these. Even that can lead to too high or low of pressure inside.

    Another way to tackle that is a two-way passive duct system with two exterior ducts (on opposite sides), filters on each of these both to filter the air and act as a flow buffer, and its interior vent at the neutral pressure plane of the structure. This can allow the house to balance itself.

    Either of these is ONLY for incidental pressure. For PH you need each exhaust to be properly balanced with MUA.


  • opaone
    3 months ago

    BTW, we don't need a 48" range. Nor do we need about 90% of what's in our house. Our cabin doesn't have indoor plumbing so certainly we don't need toilets even.

    But our 48" RNB (4 burners + 24" griddle/flattop) sure makes cooking and baking more enjoyable!

    :-)

  • Andrew M
    Original Author
    3 months ago

    @darbuka Im sure you 100% correct. But

    I do love the esthetic of the 48" range. Also I'm in Europe and very few have even a 36" range. So it's the cool factor. I'll also add that I have 6 kids from ages 1-10 so it may come in handy in a few years.


    @aklogcabin so you will be using the passive heating of the house itself to heat up the incoming air?


    Cheers

  • darbuka
    3 months ago
    last modified: 3 months ago

    Andrew, I’m not one of the 48” range naysayers. Everybody’s needs, and/or desires are different…as are budgets, and kitchen sizes.

    However, some people, and one pro in particular, never fail to negatively comment when a 48” range is mentioned as part of a kitchen renovation. This same pro also disses SubZero fridges, as overpriced and unnecessary…despite having no first hand experience with the brand.

    Yeah, I gathered you were not American, when you ended with ”Cheers!” Having spent much time in England, I’m attuned to the vernacular. Also, I watch way more British tv programming, than I do American. Oh, and my sister has lived in London for the past 30 years.

  • Andrew M
    Original Author
    3 months ago

    @opaone thanks for the detailed response.

    So you say


    "For a passive house you generally want all balanced ventilation. So whatever your range hood

    is exhausting you'll want to bring in that exact amount w/ MUA. If the range hood is on low and exhausting 400 CFM then you want your MUA to be bringing in 400 CFM.

    Keep in mind that consumer range hoods often deliver about half the advertised CFM."

    Does that mean I should get a fan/have an active MUA system or would it be sufficient passively pulling in the air due to presure being decreased?


    " Do you mean that the MUA fan is interlocked with the range hood so that it comes on anytime the range hood does? "

    Yes, that's what I meant. Perhaps in-line was not the correct jargon. I was referring to having the electrical systems working together: I turn on the vent hood and the MUA system activates.


    Regarding the canadian well: TBH I have not checked in great detail. Initially I've been thinking about installing one in order to get psasive cooling in the summer. In my area it's very rare to have active cooling as it gets quite cool at night, but during the day can get up to 95 at midday. I want to install it in the HVAC heat exchange system and basically turn off the heat exchange to draw in cool air. During the winter I suppose it would do something, but as you say, probably not a terribly wise investment.. Although I will add that labor here is quite cheap (I'm in Spain). A good plumber will charge around 20-25 an hour and I can get an excavator on premises for around 50 / hour. So the cost would be 70% materials.

    Installing a second one would be even cheaper as I could use the same holes. Almost pure materials costs, which is why I thought to use it here.


    Although perhaps it would be more cost-effective to have purely electrical duct heating?


    Thanks for the tip about having the duct heater being temp controlled.



    " Another way to tackle that is a two-way passive duct system with two exterior ducts (on opposite sides), filters on each of these both to filter the air and act as a flow buffer, and its interior vent at the neutral pressure plane of the structure. This can allow the house to balance itself. "

    In this case I'd like to make as few holes as possible in the envelope so I don't see this one, though it makes sense from a pressure perspective..



  • opaone
    3 months ago
    last modified: 3 months ago

    "Does that mean I should get a fan/have an active MUA system or would it be sufficient passively pulling in the air due to presure being decreased?"

    Yes, you need mechanical MUA. Passive will result in too much static pressure for your range hood to overcome so you might get only 200 CFM from your 900 CFM hood, it requires a much larger duct (typically 3x as large as a mechanical duct which isn't good for a PH) and it can result in air being pulled in through various leaks in the building envelope.

    ----

    Both canadian well and geothermal are geography/environment dependent so it may work for you but make sure to analyze it in some detail. Here there are lots of companies telling people all kinds of gook about 3 year payback and savings this and savings that but when you add up all the numbers it doesn't work so well.

  • kaseki
    3 months ago

    To address the MUA control, we have to make sure we know our requirements, and at present we don't have the combustion appliance configuration of the residence. The image below from a forum member shows the kind of tight control needed for combustion appliances. This is why I suggest that such appliances be in a different building, room isolated from the kitchen, or have their own MUA ducting, such as is widely available for gas and oil furnaces and hot water heaters.


    Note: inches of water means inches of water column, where one atmosphere at STP is 407 inches of water column. So 10 pascals is about a ten-thousandth of an atmosphere. Thus, we are trying to control a tiny fraction of atmospheric pressure.

    If combustion appliance safety is not an issue, then one can tolerate a somewhat looser pressure control. As seen in the graph below, the flow rate of this Wolf/Broan* blower is reasonably close to 800 CFM for +/- 0.15 inches, w.c.



    One approach is to use differential pressure sensing (outside to kitchen). This is likely needed if the problem space is complex, such as multiple ventilation fans drawing air from the space connected to the kitchen. Where only a single blower is in play, then current sensing or vane sensing in the duct can be used.

    Commercial kitchen hoods often have the advantage of one-speed operation, so the MUA can be equalized against that one case, with slight complexity introduced only in balancing the amount of MUA directed into the kitchen vs. that into the dining space.

    My house is heated by hydronic radiators, so I use a water to air heat exchanger in my attic that the MUA passes through. I use two thermostats, one for the output air and one to turn the loop on if the plumbing, mostly insulated, approaches freezing.

    Frankly, in your case unless back-drafting is a risk I would look at Fantech who as I recall have a 1200 CFM rated blower MUA system. You may need to separately provide an in-duct heater controlled by a downstream thermostat.

    _______

    *The 2023 Wolf Design Guide doesn't show the 1200 CFM roof blower.

    Andrew M thanked kaseki
  • PRO
    Charles Ross Homes
    3 months ago

    Hi, Andrew,

    Ventilation is the (often neglected) "V" in HVAC. While all homes need a ventilation strategy, the ventilation strategy for a tightly-constructed home will need to be more carefully considered than one with a high natural infiltration rate. First, you'll need a whole-house ventilation system to limit the concentration of indoor pollutants and maintain healthy indoor air. Typically, that involves installation of a properly-sized heat-recovery ventilator or energy-recovery ventilator. Second, you'll need make-up air for "high exhaust rate" appliances. What constitutes a high exhaust rate in a tight home-- like one constructed with SIPs or one insulated with spray foam (I've built both)-- is typically less than the 400 cfm which the 2018 IRC sets as the maximum kitchen range hood exhaust flow rate without make-up air.

    For your range hood, I recommend you install a pre-engineered make-up air system such as Fantech's MUAS 1200 https://shop.fantech.net/en-US/muas--1200--makeup--air--system/p111242 . Smart folks at Fantech have worked out the controls for you; the make-up air blower will turn on and ramp up/down in sync with the range hood exhaust blower. You can purchase a duct heater if you find that you need one. The control of the duct heater is a simple thermostat.

    Andrew M thanked Charles Ross Homes
  • aklogcabin
    3 months ago

    Andrew M. The cold air from outside on the bottom intake will be passively heated. Heat stacking will accur in the pipe. With the warm air on top. The is for aadditional makeup air. New air is added whenever the exterior door opens. And I will have an in line fan if I want to turn it on manually. I am also considering installing a humidistat also.

    Concerning the 2" pipe. This is for additional make up air. We have an open concept house and vaulted cieling so a lot of air. And if the stove exhaust fan or bathroom exhaust fans are on thethey will pull air through the pipe. And eventually the interior of the house will be neutral. Because it is heated it will be a slightly positive air pressure inside. This way when the doors are opened they will exhaust air, and airborne germs or odors.

  • kaseki
    3 months ago

    Suggest using an on-line HVAC calculator to check pressure loss vs. flow rate for this size pipe vs. whatever flow rate your "stove exhaust fan" is supposed to achieve.

  • Andrew M
    Original Author
    3 months ago

    Hi all,

    Many thanks for your responses.

    I see that my initial plan was over-simplifying some things and over-complicating others.

    I have seen the fantech MUA system. Unfortunately, it seems that they don´t supply these in Europe with EU voltage/frequency, and from what I´ve read there are no full MUA system "packages" on this side of the pond for residential use. Someone please correct me if I´m wrong. I´ve spent about an hour looking online to no avail.



    @Charles Ross Homes I´ve actually used a hermetic plaster to coat the interior walls as well as sealing tape along all the joints in the ceiling (timber roof), windows and doors. On the floor we´ve used a "paint" that is sort of a liquid rubber which seals as well. I won´t test for blower test, but it would surpise me if it doesn´t pass. On top of the plaster we´ve got 8CM of XPS sealed with spray foam and are going to put 70CM profiles for drywall/soft insulation.

    On the roof we´ve got wood beams with tounge and groove pine on top. Then on top of that we have a majpell 25 hermetic air barrier followed by 20CM of XPS, OSB, a moisture barrier for the roof and typical Spanish ceramic roofing tiles. Attaching a few photos. Sorry if off topic just bragging a bit heh.




    As for the HVAC system. We have planned to do something similar to what you say. A full house heat recovery ventilation system. The goal not being temperature control, but more having clean air throughout the house. It should replenish the full quantity of the house several times daily. Pending to see if I have activation based on CO2 in the rooms, etc. Will depend on price and compatability with other systems.


    In any case, this MUA problem is unrelated. There´s no feasible way that the HVAC system would be able to effectively replenish so much in lost in such a quick period of time.


    I will speak with my arquitect and the plumber to try to come up with a good solution.


    The heating of the incoming air is what most concerns me. I could get a hot-air furnace that would run on the same propane as the gas range. Based on the graphic by @kaseki, I´d like to plan for a 45-50F heat differential at around 900 CFM which would put me with a furnace or heater at around 35-40k BTU. Not sure if that is excesesive or sounds about right?


    @kaseki I think it´s clear I will need an active system. Many thanks for your detailed responses. Also for the info about the professional hoods vs consumer hoods. I was planning on going with the hood from the brand, but after reading up a bit, will probably go for a professional hood and check about in-line fan as well for noise control.



    Cheers,

    Andrew

  • PRO
    Charles Ross Homes
    3 months ago

    Hi, Andrew,

    From your description you will definitely need both a fresh air make-up system for your home as well as a kitchen range hood make-up air system. I suggest you check with the folks at the Passivhaus Institute about European sources of supply https://passivehouse.com/index.html

    Best wishes for a successful project.

  • kaseki
    3 months ago

    I think the graph suggests 50F at 900 CFM would require about 35k BTUh, or about 10 kW. This is a bit more than an electric dryer would typically use. A search term of "10 kW duct heater" will reveal several examples, including this from Fantech. https://shop.fantech.net/en-US/muah--1210--heater--12--10kw/p111290. This is an accessory to Fantech's line of MUA systems, but could be used independently, and depending on one's skill, operated at 50 Hz, 230 Vac line-to-neutral on a European three-phase mains feed.

  • Andrew M
    Original Author
    3 months ago

    @Kaseki You are correct, and I considdered it.

    Unfortunately, in Spain they limit considerably the amount of electricity you can draw from the grid. You have to contract X KW. And if I were to contract my general needs + 10KW there would be a fixed monthly fee of +120 EUR or something ridiculous for having so much contracted.


    I am considering the following setup in this order. let me know what you think:



    1) 1000kg underground propane tank (there is no natural gas, so will need something anyways for the range)


    2) 25kw propane boiler, which I will potentially also take advantage of for hot water purposes in certain areas of the home as energy is more than enough, but finding a smaller boiler costs more or less the same.

    https://calderasdegaseconomicas.es/calderas-de-condensacion-a-gas-beretta/caldera-beretta-ciao-x-25-c/

    3) Filter - Have not researched this one yet..)

    4) Then will need to add in a fan that pushes the exact same CFM as the extractor (perhaps the same model fan for both?)

    4a) I'm a bit lost as far as what fan to get. I'd appreciate any help as for examples.

    5) 13kw water air heater

    https://www.maico-ventilatoren.com/en/products/p/for-wrh-duct-systems-g6227/wrh-31-6-p8133

    6) Thermostat


    And a damper.. I could use this one if I install the damper in step 7: https://www.berbel.uk/extractor-hoods/accessories/exhaust-accessories/wall-box/

    But I think it makes more sense to install it at step 3.. So pending review.



    As far as a hood, I was looking at this one

    https://hosteleria10.com/extraccion/campanas-pared/altex-campana-basic-pared.html

    And the exterior damper will be the berbel

    https://www.berbel.uk/extractor-hoods/accessories/exhaust-accessories/wall-box/



    Cheers,

    Andrew

  • Andrew M
    Original Author
    3 months ago

    On second thought, checking again, I believe the berbel won´t work as it´s size is 6" / 150mm


    Will probably need 10" / 250mm minimum...

  • kaseki
    3 months ago
    last modified: 3 months ago

    I'll try to get back to this later today. Some early thots ...

    I assume that Spain, with its well known vast array of solar panels and probably windmills, discovered their limitations.

    Be sure that the propane tank has a proper "anode" to resist corrosion. Typically a sacrificial zinc slab planted into the ground to the side of the tank slightly below it. Needs to be accessible every decade if corrosion is an issue in the particular soil. Functionality can be tested above ground by gas tech with an electrode array.

    Hood looks like it is an acceptable configuration; would prefer stainless steel baffles rather than galvanized, if I pretended I could read Spanish. Not sure about galvi in dishwasher.

    Damper needs to be in the path from MUA intake to air exhaust via diffuser into the house. At the intake protects all the downstream stuff from the environment when closed. At the filter minimizes heat loss from the house to outside, although usually the small temperature difference > pressure difference won't allow rising heat to pass the filter. (A 2 x 2 ft cassette holding a 4-inch pleated furnace filter should have tolerable pressure loss. See table. Probably there are Euro equivalents.)



    Blowers TBD.

    Andrew M thanked kaseki
  • kaseki
    3 months ago

    It is not necessary, nor is it prohibited, to use the same blower for hood system and MUA system. However, it is usually convenient to use an in-line blower for the MUA system, and a internal hood or external roof or wall blower for the hood system. These tend to have different physical configurations. Also, if we assume that the house interior pressure is kept at exactly the house exterior pressure, and that the pressure losses from cooktop to outside via the hood system path are different than those from outside to kitchen via the MUA system path at the operational flow rate, then even identical blowers will be operating at different points on their fan curves.

    This might seem impossible looking at a typical curve, but that is because we usually only show the full power curve. If the MUA pressure loss is lower than that of the hood, then the matching flow condition will require that the MUA blower operate a less than full power.

    Further, suggesting particular blowers for someone in Spain is probably not helpful as they may not be available or may not be 50 Hz, etc. For examples, Broan/NuTone blowers have associated fan curves that can be downloaded. Fantech (inline blowers) has data available that can be plotted for a fan curve. What is the biggest gap is that hoods typically don't have a loss vs. flow rate curve. In any case, if the house has more than one blower exhaust, then the MUA will likely need some type of control that keeps the MUA within the range determined from the back-draft limits, as applicable.

    Andrew M thanked kaseki
  • Andrew M
    Original Author
    3 months ago

    Thanks alot!!!

    Will update when everything is functional.

  • David Cary
    3 months ago
    last modified: 3 months ago

    Not sure where in Spain you are located but you might be overthinking some of this in regards to temperature control.

    Where I live gets colder than most of Spain (probably all but not sure about that).

    I have a large range and a 1500 CFM in-line blower. It is pretty powerful - much better than our last house with same rating. We made sure this time with short run/one turn etc.

    Anyway, you don't turn it on maximum for more than a few minutes at a time. You might run it on low for a while. But either way, you are generating heat so that counteracts the colder air coming in.

    Yes, if it is 20 degrees outside, the area will cool down. But mostly it is welcome. If you lived in Norway, it might be too much. But I just don't think there is that much need to heat the air in Spain. If you plan on running a commercial kitchen, that might be different. Very few people are cooking with a hood significantly at 6-9 AM - the coldest time of the day. Makes little sense to plan for that unless that is your norm.

    The air in the summer will not be an issue.

    I have a heat pump - 2 tons downstairs for 2400 sqft or so. It just isn't a problem - the house heats back up.

    Spain does not have that much solar - NC has more per capita. CA has double despite less people. On wind, it is basically Texas which is fairly high. No one calls modern wind a "windmill". Demand management is just basically a good idea regardless of electricity generation.

  • kaseki
    3 months ago

    2 tons is 24k BTUh, which could offset a 30F differential temperature at 1000 CFM actual. See my MUA heating chart way up this thread. You will have a cold draft while cooking during a higher differential temperature cold night with high air-flow rate.

    I have a 120k BTUh furnace that can in principle move that much heat through my MUA heat exchanger if the air flow rate and temperature differential will allow that much transfer, but in reality on a cold night part of that will be going to some combination of hot water heating and multiple room heating. In S. NH USA, a number of nights are colder than 0F ( -18C) in the winter, and pulling an actual 1000 CFM through my hood for stir frying will lead to a cooling draft from my MUA diffuser. One's MUA design requirements should include a spousal cold draft threshold.

    Historical windmills milled grain into flour; modern windmills mill taxpayer/ratepayer dollars into enormous piles of un-recyclable scrap and dead birds.