But here is the thing. My attic has no soffit vents. It has a ridge vent that spans the length of the roof (the interior of the house measures 25.5’, so without going into the attic to measure it I would say the vent spans 25’. 24’ if you want to be conservative), and a 12"x 12" gable vent on each side. I read online that a ridge vent offers 18 sq. in. of ventilation. So that means that at 25’ the ridge vent gives 3.125 sq. ft. and 3 sq. ft. at the 24’ measurement.
The unit requires 3 sq. ft. of ventilation. So it looks like it would be enough.
It looks to me like it works out, but I just want other opinions before I buy it.
And I was reading about the importance of soffit vents, and am looking into installing them, but looking at the construction of the house, I am not sure that is actually possible. The house has almost no eaves. I will need to crawl up into the attic to check that out.
Any thoughts or other options would be greatly appreciated.
Let me discuss why we want to vent our attic … it’s important to keep the temperature on both sides of asphalt shingles the same, to prolong its life span … typically the inside of the attic space is warmer than the outside air, so we wish to draw that outside air in so the temperatures to equal … with your ridge vent, we have a way for the hot buoyant air inside the attic to escape … and we need soffit vents to allow outside air in … our living space is below this, and this is why we put our R-38 insulation at the bottom of the attic space … we want our inside to be 25ºC even if it’s -20ºC outside, and we want it to be -20ºC in our attic … remember that, the second floor ceiling is where we want our heating to stop …
Not much for eaves … damn … there ought to be a law … anyway, you’ll need a lot of small holes then, through the eave and into the attic, and we’ll need some manner of baffle so the insulation doesn’t block the air flow … I have 575 holes of 1/2" diameter for our three square feet … ouch … but some are better than none, and each hole will need to be covered with bug screen or you’ll have wasps’ nests in your attic … but 1/2" is pretty small, so hopefully there’s room for holes a little bigger …
Alternately … we can rely on the eaves not being very air-tight … if our second-floor ceiling is dry-walled then that should be mostly sealed … we can set lil’ box fans pointed out at the gable vents and hope enough air leaks in through the eaves that the temperatures will be equal (outside = attic) … there’s units we can buy with temperature sensors for both outside and in the attic so the fans only run when we need them to …
This contraption you linked to is insane … what this does is draws the -20ºC air into the heated portion of the building, where is should be 25ºC … and pumps 25ºC air into the attic portion, where it should be -20ºC … maybe this is a good idea in Southern California, where it may take ten years to notice we have a roof leak it rains so little, but most anywhere else this thing is a bad idea … you didn’t say where you lived, but I’d say this is completely bogus and a waste of money … better to leave the exhaust in your living space for circulation …
Venting the attic is less of a problem with wood shingles … and I think not a problem at all for metal, cement or slate roofing … it’s asphalt that has nasty thermal expansion properties, noticed how hard it is to seal asphalt-to-metal joints …
You don’t say where you live or your purpose in installing a whole house fan, so I can’t tell whether a whole house fan would be a good idea or not, but I have paid to remove two whole house fans. In the South, I could keep the lower floor of my brick-clad house cool by using the whole house fan during the night, but I gave up on that quickly because of the uncontrolled humidity. Hot, 90% RH air entering a cool space makes for warm, 95% RH air which is good mainly for mushrooms. In the second house, in the Northeast, I did it because taking out the whole house fan is the best way to prevent warm air from escaping into the attic in the winter and conditioned air from escaping into the attic in the summer.
A whole-house fan is for summer, not winter. The idea is to draw 25° air into a house and blow the 30° air out through the attic. We had one in Maryland and it worked pretty well. You open windows and suck in air in the evening when it starts to cool down outside.
Exactly. It’s simply doing a more thorough job of what you are doing when you open a window at night and set a fan in front of it. Works in a climate where it often cools down a lot at night when it’s too hot during the day. Best if it’s generally dry, too. Fortunately, this describes much of the American west. With luck, you get the house cooled down enough overnight that you can close the windows and blinds in the morning to trap the cool air in and run the air conditioning less, or do without it without too much discomfort.
When mine was installed they were pleased that I had adequate attic ventilation. Many houses don’t. It’s also not an automated system. It’s imperative that you don’t run it without a lot of windows open to avoid putting to much strain on the motor.
We had one removed also. Humidity was horrible. We liked it running at night. All that moist air came in the windows and straight through the attic. It can cause mildew or mold in the attic. We didn’t even realise it was happening. We were just tired of trying to re-cool the house is the day time after the AC being off all night.
I would think it would be the opposite. The more windows that are open, the less force the fan has to exert to pull the air in. Extend this to an extreme: Suppose you have only one window open a tiny crack. The fan has to try to suck a large volume of air through that tiny crack, creating a negative pressure in the house, and a big load on the fan. Now go to the other extreme: you have no walls. There is no pressure differential inside vs. outside and the only significant load on the fan is from pushing the air into the attic.
Hmmm. Is there a difference between what you guys are talking about (sounds like venting outside air in to equalize temperature in the attic, or perhaps venting hot attic air out) and the type of fan that’s mounted in the attic, yes, but also facing downward through the ceiling?
A friend of mine in high school had a ranch home and his parents had one. When it was off, metal louvres were closed over the fan, which was mounted in the hallway ceiling of the house. The switch to turn it on was also on the wall in the hallway, and when you turned it on the louvres opened and the fan roared to life, blowing massive quantities of air downward to generate a strong breeze throughout the home. IIRC it was pretty loud but worked really well when it wasn’t too hot outside. I can’t remember if they opened the windows but I know when they ran it they always kept all the doors to all the rooms open.
Seemed like it was better suited for warm Spring and Fall days when without it or a/c on the inside of the house would get significantly warmer than the temperature outside due to ambient warming and sunlight.
This still defeats the purpose of the attic venting … if it’s 25º outside, then we want it 25º in the attic … if we want it 25º in our house, just lower the upper sash the same amount we raise our lower sash … that’s the whole point of double hung windows …
Plus we’ll have to get up in the middle of the night to turn the fool thing off … it’s nice pumping in 15º air to replace the 30º air … but when the outside air is 7º or 8º, then maybe we don’t want to pumping outside air in … doesn’t matter if it’s 40º in the afternoon, we’ll need a sweater first thing in the morning in the American West …
In 1954 (when home air conditioning wasn’t common) my parents bought a home that had a whole house fan. The house was basically 3 storeys with the third floor partially finished. The fan was installed at the top of the stairway and the part of the stairway on the third floor was enclosed. There was maybe 15’ between the fan and a wide open window. We ran the fan only on summer nights and it did a wonderful job. We basically opened every window in the lower 2 floors and it cooled the house down during the night. Then we closed everything up during the day. This was in suburban Philadelphia which gets loads of hot humid weather all summer. Mildew was never an issue.
Montreal doesn’t have the same kind of weather as Philly. Nonetheless, it gets some (and has had some hot humid weather over the last month) and I once inquired about a whole house fan, only to be told that it is against code. If I had one, it would require opening up a hole to the attic and probably opening up vents in the attic that would have to be closed for winter so I am not sure it would have been a good idea. We do try to use exhaust fans now that we are empty nesters.
First, not everyone has double hung windows. Second, realistically most people have little concern for the temp in their attic, even if maybe they should. They just know that it’s still hot inside and nice and cool outside and they want a good way to expel the hot air and bring in some of the cool. They won’t be using this in the middle of winter like the example in your first post. So if it’s 72 outside (with ideal attic temp of 72) and 80 inside, how much damage is it possibly going to do to make the attic 80 for a couple hours until it evens out again?
I’d really be more concerned with Yeah’s concern about heated/cooled air escaping to the attic through the vent when you don’t want it to.
Why would you vent a whole house fan into an attic, and not directly outside? It’s basically a large bathroom fan. I wouldn’t vent my bathroom fan or my drier into the attic, so why would I vent a whole house fan into the attic?
Cutting into the roof isn’t a good idea. Skylights and roof vents are the first part of failure and prone to leaking. If the attic has its own venting, then the attic is passively passing the air through.
An attic fan (venting the whole house into the attic or outside) is just the ticket for some climates, like mine. It ads a little breeze to a warm, but not blazingly hot, summer day. With Lake Michigan in my back (front?) yard, it never gets as hot as inland cities, and air conditioning would be overkill. Closing the house for air conditioning would shut out the outside sounds that I like to hear, like the waves.
I’m going to guess someone installed this wrong - I’ve been in a number of houses with attic fans and they all suck up into the attic. It’s the same air flow requirement, but I don’t see why you would want to initially blow all of that hot, dank attic air into your house.
I need to get our fan replaced. We use it spring and fall when the humidity is lower. It no longer self-starts - if you turn it on, you get an electric motor hum. But if I open the louvers and give it even a light spin, it starts right up. If I spin it the wrong way, it will run backwards (and keep the louvers closed tight), which is what makes me think the one FoieGras is familar was wired wrong.
As to turning it off in the middle of the night - ours originally had a timer on it, but I took that off (mostly because it was a one-hour timer and worthless for its purpose). We turn it on in the late evening (when appropriately cool outside) and off when we get up. No one is home during the day, so even if it cools down to the low 60’s over night, it is comfortable when we get home after work.
I purchased a 16" window fan that I put in the cat/junk room of our 1400sq ft house. It works great for creating a mild breeze and removing any odors from cooking, etc. I had a whole-house fan growing up and it could suck the paint off a car, was loud as hell, and created way too strong of a breeze indoors as it had no speed control. I thought I would be disappointed with a window fan this one has worked great. Highly recommended if you have the window space.
Perhaps I misunderstood which way the fan was actually pointing due to the fact that when it was on it always generated a pretty large breeze throughout the house, cooling it down.
Regarding the dumping of heat and humidity into an attic issue:
Heat? The attic is going to be hotter with the fan off than with it on. Attics in the summer are hotter than the ambient outside being pushed thru.
Humidity? The attic with the fan off is going to be the same humidity as the ambient outside air being pushed thru. So no real net change. If anything the air movement will prevent moisture buildup on the structure.
We have an attic fan that engages when it’s 80F. We have an old Victorian era home with lots of vents in the attic. There was no attic fan until about 10 or 12 years ago. It doesn’t seem to make any difference, so I’m not sure it was even necessary. All it does is pull in air from outside and move it around.
Attics are required by code around here, but in new builds they just seem to be heavily insulated and not used for anything else. In my son’s new home (4 years old), the attic supports wiring for ceiling lights on the 2nd floor and nothing else. It’s chock full of insulation. I haven’t seen any soffits on his house. I’m not sure there’s a ridge vent either, but am not certain. The roof is more of a mansard type so it’s not like there’s a prominent center ridge that makes a ridge vent obvious.
I’m not sure that roof venting is something you have to do in modern homes. What you could do is make a call to the building inspector’s office in your city/town and ask some questions. If your home isn’t all that old, it may not be a benefit to have such a fan. Or, if you have a friend or acquaintance who is a local builder, you could ask them about what type of house configuration would benefit from an attic/whole house fan.