Call your local code official and ask what are the make up air requirements. Speak to the person who will do the actual inspection. You may get input from the forum but ultimately it is the inspector who decides if the minimum code requirements have been met.

Wowie, a 5,000 CFM exhaust-only fan in a moderately well built house sounds like it'll pop your ears, flush your toilets, and back draft everything if you didnt have all the windows wide open.

Is there some benefit to this whole house fan that a well designed HVAC system couldn't do better, for less $?

"Is there some benefit to this whole house fan that a well designed HVAC system couldn't do better, for less $?"

- A whole house fan is considerably less costly than running an HVAC system. You can run a big blower or you can run a big blower and compressor and ventilator. Most estimates are that a whole house fan uses about 1/4 to 1/10 as much energy as an HVAC system to accomplish a similar level of comfort*. Payback is likely less than 1 year. From a financial standpoint this is a very easy decision.

- It's healthier. We are becoming increasingly aware of the problems that living in sealed houses (and other buildings) without adequate fresh air can cause. The CDC have begun a study to better quantify this with many expecting a 4x increase in current ventilation recommendations.

- More pleasant. You can hear what's going on outside (assuming it's something that you want to hear) and the breeze from open windows is quite pleasant.

- It can cool a hot house much faster than an HVAC system.

Anecdotally..., we sleep much better on nights when windows are open and we have considerable fresh air coming in than nights when windows are closed and our only fresh air is from our HRV. Our house is more pleasant during the day when windows are open. FWIW, our HRV provides about 1.5x the current recommended amount (in the U.S.) of fresh air.

* This is assuming appropriate weather conditions. For us about 40-85°f seems about the range. Below or above that for long periods and we'll likely turn on HVAC. Higher humidity might reduce this range a bit.

At our former cabin where our new house is being built we went 2 summers without using our HVAC system at all except for brief periods to make sure it was working OK. Most years I'd guess we reduced A/C system usage by about 70%. It will be different when we're living there full time but I'd guesstimate about 50% less A/C system usage on average.

@mike_home, sadly everyone on our team believes it'd be a bad idea to call the inspector. They believe that there's a higher likelihood of the inspector not thinking about the whole house fan than of their thinking logically enough about it to say that it's OK without MUA.

In my dealings with our inspector I think he'd think through it logically but our builder, architect and HVAC folks think otherwise.

The way the code is written, yes you do need that automatically engaged MUA. It would be an alternate and less accepted interpretation to think that it did not.

Isn't the idea of a whole-house ventilator to open the windows when in use? So wouldn't a separate MUA system defeat the purpose?

Isn't the idea of a whole-house ventilator to open the windows when in use? So wouldn't a separate MUA system defeat the purpose?

Inspector: Yes, but you must have an MUA because my book says you must.

:-)

I've found that engaging with the inspector AS A HOMEOWNER is well received.

Some examples - we have a Lot of retaining walls. In the beginning of the build, we met the inspector, reviewed the engineering drawings, showed him what we were doing, and got him comfortable that we were NOT trying to get over on him (sadly, like too many builders do...) and he was genuinely interested in the build. Subsequent inspections for structural items involved him checking the drawings, and then taking pictures to send his boss. He then informed us that if we won the lottery, he'd want us to build his house.

Second - for plumbing and electrical, we are using Legrand cable tray suspended from our bar joists, with MC cable for wiring, and then suspending copper plumbing below the tray from attached uni-strut. We engaged with the inspector and asked for his help BEFORE starting either but showing him the installation of the cable tray. He said he had no issue with this method as long as the plumbing stayed below the electrical (of course)

We've found that most of the time, inspectors see what we see here in the "normal" build - large scale builders trying to get away with the bare minimum or less and the relationship is rather adversarial. Taking some time to discuss, and also showing that you have done your research (and perhaps have this idea designed by a professional (HVAC / energy rater / indoor air consultant, etc) gives them confidence that you are doing this for the RIGHT reasons and they can find a way to help.

YYMV - but my experience is that inspectors appreciate homeowners wanting to be involved, do different things, and who take the time to engage with them in a collaborative way vs the "normal" adversarial way. I am not surprised you've been advised against engaging with the inspector - we were too. Again - I believe this is because most building "professionals" come into this expecting a more adversarial relationship with the inspector than we do as homeowners.

I really like your idea of the fan - only wish that we lived in an area that the humidity levels would allow such an approach!

Well I can certainly side with wanting good indoor air quality.

I suppose it all depends on where you live. Where I am, It'll be just right to have the windows open maybe 5 days/nights out of the year. Otherwise it's either to hot, too humid, or too cold.

I'll be using air source heat pumps, with an ERV system, with focus on air tightness and insulation levels.

But for indoor air quality, the thing I think everyone 50-100 years from now will look back on us and think we were stupid for not incorporating: PLANTS!
Thats what actually brought me to this site, snake plants / sansevieria. Great for air quality, don't need much water so wont make the house more humid.
Lock yourself in an air tight box with 30 of those and try to suffocate - you wont. (please don't actually try this)
There's already science supporting this idea, but I'd love to see more.


I digress, here's an article on whole house fans from green building advisor which you've probably already read: https://www.greenbuildingadvisor.com/article/fans-in-the-attic-do-they-help-or-do-they-hurt

Why don't you just wire and set up blocks for it and install after CO? Is this impractical for a modern WHF?

I won't talk about all the things planned after CO for us....

In most climates a WHF is an energy loser because it doesn't seal appropriately. WHF when 85 out? - that is not normal human behavior.....

Nowadays a HRV is what keeps your indoor air fresh. This is the way to do what you want. WHFan is for leaky houses where that leakiness makes them safe. Older builds were fine. So it depends on how you build.

I'm not sure what is meant by Makeup Air - is it simply an opening to the outside which allows sufficient air to come in, or is it another 5CFM blower? My feeling about whole house fans is that in the summer, it pulls in cool but very humid air (at least here on Long Island). That's not what I want. For my upstate house, there is an HRV which keeps the interior air fresh, although in the spring and fall, I simply open the windows!

opaone, How is the "team" going to handle the make up air requirement? Install something and keep their fingers crossed the code official will pass it?

I too am interested to find out what is "make-up air". Thx for any info.

From a medical and general health perspective an HRV/ERV (along with other avenues of ventilation such as bath and range exhausts and doors opening) does not appear to provide enough fresh air in to a moderately well sealed house. Current guesstimates are that houses need about 4x current recommendations but we'll have to see what the new reports say.

What we do know is that we (in the U.S.) are much less healthy than people in all other developed countries. The top of the issues list, by a wide margin, is lack of physical activity. Poor diet is believed second. An increasing number of coming to the conclusion that lack of fresh air and too much time in stale (and moldy) indoor air is third or possibly even second. A sub element being looked at is that this latter has lowered our immune systems and increased allergies to our natural environment.

What we do not know is how much more fresh air needs to be brought in to our houses than is currently brought in. And this is likely quite variable. Twice as much may improve health somewhat but still cause some 'stale air related illnesses'. 4x may eliminate most or all stale air related illnesses but not reduce mold spores and related diseases. How much is enough is likely to be a great big huge grey area.

Make Up Air or MUA is air brought in to a house to compensate for air removed by exhausting appliances such as range hoods, bath fans, central vacuums, fireplaces, or naturally aspirated furnaces & water heaters. In older houses there was enough natural leakage through walls, windows and doors to provide this but as houses have become more sealed we've realized the need for specific make up air. This can be passive (such as an 8" duct from outside to a bucket in a mechanical room) or active (in-line blowers that pull air in from outside).

How much fresh air is enough? More :-)

...In most climates a WHF is an energy loser because it doesn't seal appropriately. WHF when 85 out? - that is not normal human behavior.....

The after CO avenue is one I'd rather not go down but, yeah, we'll see :-)

Modern whole house fans such as the Tamarack HV5800 (https://www.tamtech.com/HV5800M-Cyclone-Whole-House-Fan_p_163.html) are insulated and seal up pretty well when not in use. We'll likely build insulated panels to put over the intakes during winter for extra protection. For us in MN the energy savings in not running A/C blows away any costs from poor sealing.

With a bit of breeze, either naturally or from a fan, low 80's can be comfortable if humidity is low. A bit of higher humidity and we'll have the A/C on though.

A tough bit to figure out is when humidity is low enough that it's comfortable (or marginally comfortable and the benefits of fresh air outweigh any slight heat/humidity discomfort) but will cost more to de-humidify later than it would have to keep the humidity low the entire time. I'll likely always lean towards fresh air though and pay the minimal extra cost to dehumidify.

The Whole House Fan comes with operating instructions? It should say "open windows during operation" which would provide the required MUA. Those instructions should be accepted as code, the language the inspector speaks.

So you put in this fan and no MUA, Where does the air come from? A window can supply some. Some can come from the vent pipe from your gas water heater, or gas furnace exhaust or dryer or fireplace. If you have a well sealed building shell these may be the easiest sources even if you have a window open but especially if you only open it part way.

On a nice day with a breeze we'll often open a dozen windows or more - six per side. That s/b more than sufficient. And as I mentioned there will be a lockout requiring x windows to be open before it can be turned on. Furnace and boiler are sealed combustion so no problem. Dryers have exhaust blowers so similarly not a problem.

You could likewise argue that people shouldn't put in range hoods. Because... What if the breakers for the MUA trips or the MUA filter is clogged or the system that triggers the MUA fails or the MUA motor burns out or a mouse with a dense bone structure gets in there and keeps the blower from turning.

I grew up with an attic fan. It was great in Kansas, a place with very hot, dry days, but cooler nights and very low humidity. But even there, it became a real problem for me during hay fever season in the fall. All that pollen being drawn into the house. My parents had to buy a windows AC for my bedroom.

I now live in KY, the home of "mugginess". It also is the home of what is known locally as the "Ohio River Valley Crud". People who have never suffered from allergies before, succumb to them after living here a year or two. AC is the only way to go for us - an open window allows tons of pollen into the house, as well as pollution. And that humidity.

If I had my choice and lived in a lovely climate, I would much prefer open windows. But with allergies, this is simply not possible. I would never build a house without an HVAC system even if one hopes to have windows open a lot.

Opoane - the medical fresh air argument is spurious. There is talk that the current fresh air requirement is too high. Measure your NO and VOCs and see. Buy some plants and open some windows. Just remember all that negative pressure will also pull up the radon from underground. It can also pull VOCs in from your OSB sheathing.

Air conditioning in MN is a tiny amount. Down here in NC, we spend 3x on heating. In MN, I would expect it to be 10X but it would depend on insulation and air sealing of course. It is not uncommon to have 20% of winter energy use to be infiltration. Not uncommon at all. Just look at all the talk on green building forums about WHFs .. oh wait, there isn't any.

None of that matters - because you want one. But don't try to use the energy argument - it just doesn't wash. Put all that energy into solar or foam sheathing. Heck I want one but I will probably just use my range hood - which does have MUA. Filtered MUA and doesn't require opening windows.

Opoane - the medical fresh air argument is spurious. There is talk that the current fresh air requirement is too high.

Too much fresh air? Have you informed God about this apparent design flaw with our world?

More seriously, given what I do for a living I can tell you that you are likely very far off base on this statement.

To your other good points.

I heartily agree with you about plants! Measuring NO & VOC's are problematic because there is still a lot that we don't know. We can mostly know when air is not good enough but we don't yet know when it is good enough.

Radon shouldn't be a problem. Firstly air (a gas) takes the path of least resistance. Even with too few windows open creating high static pressure the path of least resistance should still be the windows and secondarily, as you mentioned, the wall systems. Second, the radon capture/exhaust system should continue to operate when the Whole House Fan is on. Finally, even if there is additional radon pulled in we are increasing the air exchange rate of our house from 340 CFM (two 170 CFM HRV's) to about 11,000 CFM. That's a lot of fresh air flowing through and a lot of stale and potentially radon filled air being exhausted. The risk is if it begins pulling radon in and some residual amount remains when we turn the system off. Off the top of my head this is extremely unlikely but should be able to be mitigated by running the system at lower speed (and thus reducing the internal vacuum but still exhausting stale and radon laced air) for a bit before turning off completely.

Sheathing is all plywood rather than OSB so VOC's s/b much less though still there. Similar to above, the path of least resistance s/b the open windows. Running the system at low speed for a bit before turning off should reduce or eliminate this problem?

A/C in Minnesota is indeed tiny compared to NC. I grew up in AL so have some familiarity with it. We also had no A/C until I was about 10 when we installed a window unit in our family room. I didn't live in a place with central air until I installed it in the house my GF (now wife) and I purchased in 1985. Even so it is still quite expensive to run each year and massively more expensive to run than a WHF. As I said above, you can run a giant blower or you can run a giant blower+compressor+air filter+ventilator. On average during warm summer days an hour of WHF will likely use about 1/10 the energy and cost of an hour of full AC system? Am I missing something?

The fresh air requirement too high from an energy standpoint is what I meant.

An hour of WHF might use 10% of the energy but it doesn't do the same thing to the inside air so it is a false comparison. Of course it depends on the outside air but humidity is the real issue.

If you don't open windows there is a chance you draw radon into house. Of course opening windows changes that dynamic. This is the first I heard about a lockout requiring windows to be open. That would seem to be enough for the code inspectors but really aren't you fighting a potentially costly battle? Do the lockouts require fully open windows or just not closed? After CO is much easier.

So are you a pulmonologist or immunologist? Or environmental scientist?

What will your HRV be set at for flow for the 6 months of the year that you won't run the WHF? If IAQ is so critical, would not living in CA be wiser? Or maybe CO? Seems like an obnoxious question - didn't really mean it to be.

I have never seen any hard evidence that IAQ is anywhere near as important as diet and activity. But I am open minded. Also not sure 5000 CFM necessary for IAQ.

A/C is cheap. A reasonably designed system should be $100 a year or less in MN for even a large house. My 5,000 in NC was $200-$250 with ducts in a hot attic. We slept at 65 all summer. When I looked at WHF with install, it was not cheap.

The humidity issue is very real, and potentially more deleterious to the house’s health than lesser air exchanges. You will need to calculate where the dew point exists in your specific wall sandwich ingredients. And then look at the temp and humidity charts to be sure that you aren’t creating mold inside your walls by inviting the moisture inside.

A/C is cheap. A reasonably designed system should be $100 a year or less in MN for even a large house.

Wow, that must be nice. In SoCal where I live, running an A/C probably costs..... $500/mo in the summers? My friends in the desert have a large house, and pay about $1,200/mo. I'll stick with my WHF.

My gas/electric bill combined is about $250 a month! When one lives in an area with year ‘round high humidity, WHF is simply not an option.

Anglo - you don't live in a new house I take it? You may want to get an energy audit. I currently live in a 1980 house and $200 tops with 2 EVs. No reasonably sized house should use that much in the South.

It's a 1948 house. When we added a full dormer on the 2nd floor (1 1/2 story house), they put in loads of insulation, but there is little attic. The ridge vent helps get heat and humidity out of the house. Both upstairs and downstairs HVAC units are "energy efficient", and the entire house has recently installed Marvin windows (alum-clad outside, wood inside - SDLs). The house is brick and exterior walls (except dormer) are plaster as are most walls/ceilings except where repaired/replaced. There is also a full basement and basement garage.

I'm home all day so no turning back the heat during the day i the winter, but upstairs heat is only on when it's very cold outside, and then set at about 65 - off completely at night). When AC is on, downstairs is set at 73, but upstairs is set at 65 - like to sleep in a cold room.

HVAC is gas/forced air. Water heater is gas. Stove is gas. Electric clothes dryer (only do about 2 loads a week).

It is what it is. At my age (75) I have no intention of spending a fortune to re-insulate the attic - it would take a long time to regain that investment.

Anglo - what you need is better air sealing. I suspect the humidity is high in your house because of all the air infiltration. That is why you need the temp so low to be comfortable. Your HVAC units are probably oversized so they don't remove humidity as well as they should. Sometimes a new thermostat can force longer runs for better humidity removal. Also running a timer upstairs so that it doesn't cool that low in the heat of the day can make a difference. The timer also forces a really long run time before going to bed which aids in humidity removal.

So changing stats and finding air leaks could have a pay off in short time and also aid in comfort by reducing humidity.

Honestly so many central units are so bad (duct leaks and ducts in unconditioned space) that adding a minisplit could make a big difference also.

Have you sealed your crawl?

Either way - a 1948 house in the South puts you in the oldest 5% probably - and so you pay what you pay but that isn't normal or average.

Mrs. S - CA electric rates are 2-4x the typical Southern rate - when you tier. But we have humidity so we can't do WHF. There is nowhere in the SE that pays over 12 cents a kwh total.

"but what if the system is down or the fan accidentally comes on while all the windows are closed"

It will be the end of western civilization!

Opaone,

I'm not sure what the building code requirements are in your locality. The 2015 IRC requires mechanical ventilation (to maintain indoor air quality) if a blower door test of your home indicates fewer than 5 air changes/hour.

Unless your home requires mechanical ventilation and your HVAC contractor is proposing to use your whole house fan to meet the requirement, I think he or the inspector is confused (the alternative that I'm confused, is not one I like to entertain, but happens more frequently the older I get.)

Your whole house fan is an alternative to air conditioning. Unless you're planning to run it 365 days/year and it's designed as part of a system to meet the requirements for mechanical ventilation, I don't think it can be used to satisfy the requirement.

When you run it, it will require make-up air to be supplied at a rate equal to the exhaust rate. This can be done simply by opening the number of windows needed to provide the net open area for the particular fan. Alternatively, a make-up air damper can be installed.

You might want to re-post in the HVAC forum and let the HVAC nerds have a go at it.

Best wishes for a successful project.

I'm just wondering...

What if opaone installs the whole house fan, turns it on without opening any windows and the whole house is sucked up and everything simply disappears...

Hope we keep hearing from opaone so we know all is well...

What if opaone installs the whole house fan, turns it on without opening any windows and the whole house is sucked up and everything simply disappears...

I wonder if I could charge admission for people to see the only black hole on earth? :-)

Whatever you do, don't turn the fan to the high setting...!

We were once trekking up to 'The Old Man of Stor' and there was an American behind us providing a constant stream of commentary about the lack of steps, rails, emergency phones, lighting, gravel, signs, posted maps, and I'm sure a few other things. Later we learned he was a code enforcement guy for Passaic NJ.

We ran in to him again later at a local café where he was criticizing all of the people in the village riding bicycles without helmets. The fact that a bicycle rider there is 1/4 as likely to be killed per km ridden as one in the U.S. didn't phase him.

Ok, so the issue is that a whole house fan can backdraft water heaters, clothes dryers, and plumbing traps. So it can pull carbon monoxide and methane from sewer gas into the house. That's bad. That's probably a more real and present danger than potentially radon and voc's.

I totally get it why windows aren't considered makeup air - it's too easy not to have them open or not open enough. And I also get it that this requirement is in the code and it's unlikely to be ignored.

I think you are going to have to look at an atmospheric damper that provides makeup air - and if you have the windows open enough then it stays closed.

Whatever you do, don't turn the fan to the high setting...!

:-)

That would be 11?

So Jake, you are saying that negative pressure is going to pull gases through a sewer trap? That seems unlikely. I would like to see calculations showing that it happens. Obviously it is possible, it just seems unlikely. CO from a garage definitely but pretty sure OP drives EVs.

"...That would be 11?..."

Unless you have a setting with 15 or 20...

If you don't open windows there is a chance you draw radon into house.

Yes. And if you don't close them when it's raining you'll get wet inside. If you don't press on your brake pedal when approaching a junction with lots of cars going through it you're likely to crash. If you don't make your way to a restroom when necessary you're likely to offend some people with the results.

How far do we carry idiot-proof? We've planned a lockout that won't allow the WHF's to be turned on unless x windows are open. The sole purpose of the fans is to pull air through open windows when there is otherwise no breeze.

Interestingly, if you open some windows on just the leeward side of a house you could likely create greater interior negative pressure than WHF's would. Or open only upstairs windows and watch how much negative pressure on lower floors (and basement Radon) stack effect creates?

(BTW, I do appreciate your reply. But I do seriously wonder how far we carry idiot-proof. I think it's good to think through the negatives but at the same time we need to think through how critical these negatives are, particularly with regard to the positives of increased health and less wasted energy).

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An atmospheric damper isn't a bad idea but to be properly effective would need to be 4'x9'. I don't want any more penetrations than necessary and certainly not a 4'x9' beast. Maybe a larger passive MUA option (16"?) might be enough to pacify the code folks though.

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BTW, garage CO shouldn't be a problem as our cars are electric. OTOH, I'm not sure if there aren't gasses from the batteries.

All those that have turned on a whole house fan without opening windows raise your hand.

Ah HA! . . . just as I thought!

I grew up with an all house fan and loved it. The codes IMO.....seem to make NO sense. It seems like its in favor of the HVAC folks. NOBODY would turn the fan on unless windows are open and it can't turn on by itself!!

Nobody would plug the toaster in the kitchen with their right hand, while holding the faucet with their left hand. But the code says the outlet has to be ground fault type in case you decide to do this.

In a tight house the whole house fan is a potential safety issue. You can argue with the code official that it is not, or ask him what is required in order to meet the code criteria.

mike_home

" Nobody would plug the toaster in the kitchen with their right hand, while holding the faucet with their left hand..." Except, of course, those who have done exactly that. Or in my house where the counter is stainless steel... etc.

You can talk about "Nobody would do_____" but the truth is that people can't and don't think through all the possibilities (such as backdrafting gas appliances and sewer traps) or even the obvious things like having the curling iron near the tub.

Mike_home is right, you can argue the code - and I don't think you will get far, or you can find out what's needed to meet code.

These recent comments have made me remember the tag on our new clothes iron that said, “do not iron clothes while wearing them.”

Sigh. Lol

“do not iron clothes while wearing them.”

An image comes to mind similar to one inside the Jazz album by Queen.