Whole house fan experiences?

[RachelV]

We just got a whole house fan installed in our new place, and it's the only cooling we have (no swamp cooler, no central air). While the upstairs was cooler this morning than it's been since we moved in, I have to say that it wasn't quite as cool as I was hoping it would be.

Granted, it's been HOT up there during the day -- probably getting up to the mid-80s in the late afternoon, and then cooling down to about 75 overnight with some aggressive window-fan placement. Given that, this morning's 68ish was really lovely, though since the low was around 60 I was hoping for a bit more.

So, I guess my questions are, for those of you with whole house fan experience -

Roughly how much cooling do you see overnight, relative to the max temp your home gets to during the day? Is it reasonable to expect that the interior temp will get close to the overnight low by around 6am? I'm also hoping that now that the upstairs is cooler, we'll get better results in the future -- in other words, the upstairs won't get to 85 today, since we're starting at 68 or so instead of 75 in the morning. Does that match other people's experience?

Any tips for the best window-opening strategies? We have 3 floors, each about 600 sq ft. The bottom floor is a basement that stays cool (hasn't gotten above 70 yet) without any fan intervention, so we can easily close the basement door at night and just worry about cooling the top 2 floors.

We're in Boulder, so the worst case is near 100 during the day and low 70s at night. More typical for the worst of the summer is high 80s during the day and low 60s at night.

 

[SBrown]

We have a/c and an attic fan (older house, I assume the a/c was installed afterward). On hot days, it still gets really warm upstairs, but the basement is a meat locker. Before we go to bed, I open the upstairs windows and the basement door, and turn on the fan for a few minutes just to suck out that hot air, and suck up the cooler air from the basement. So give that a try. I don't know how your doors are configured (and I'm no expert at all on this), but I can stand in our foyer and feel the cold air moving up from the bottom level. After things cool down a bit, I seal back up and turn on the a/c, which then doesn't have to work so hard.

Don't know about your other questions.

 

[Bill Talbot]

It has to do with the mass of your home, what temperature it is saturated to and what the overnight low will be. You will lose a bit more each day if you have a series of hot days.
With night time lows around 70 you will not recover. For that, in a dry climate like Boulder, a Swamp cooler can help a lot.
Whole house fans are great and economical to run for all but the hottest weather. But they can only do so much.
Pull air in from the lower north or east sides in the evening for best effect. Keeping the sun out, especially on south facing windows and doors can help a lot too.

 

[Monique]

FWIW - I can't speak to your actual question, but it is kind of crazy how much better our recent A/C system works than the original (1998) - and it's cheaper to run, too. Of course we'll need to own it for pretty much its entire lifespan to actually recoup the electricity savings financially. But my point is - the first guy we talked to was adamant that due to our duct sizes, there was no way we could do much better than what we had. We left it alone for a few years. The second guy had a very different story, and obviously was correct, based on what we're now experiencing. So I don't know if there is some other option or as people mentioned, fan placement that might do better for you.

Then there are always those nifty home made A/C units using ice and a fan ;-) Since you don't expect a ton of days to be this hot, that's an option.

Or come visit. Eric keeps our house like an ice box.

 

[RachelV]

While it's true that a swamp cooler would help a lot ( ), we're gonna stick with whole house fan only, both because we're cheap, and because it really is enough in this climate in all but the worst weeks. We've had a bit of a hot summer so far so will be interesting to see how the whole house fan does in the less-than-ideal case.

 

[Bill Talbot]

While it's true that a swamp cooler would help a lot ( ), we're gonna stick with whole house fan only, both because we're cheap, and because it really is enough in this climate in all but the worst weeks. We've had a bit of a hot summer so far so will be interesting to see how the whole house fan does in the less-than-ideal case.

Well look on the bright side Rachel, you don't have to deal with the HUMIDITY. (that you know well from NYC and CT)
I envy you for that...

 

[RachelV]

Well look on the bright side Rachel, you don't have to deal with the HUMIDITY. (that you know well from NYC and CT)
I envy you for that...

Oh, I know. Every time I get cranky about the heat out here I try to remind myself to be grateful that it's not also 90% humid. It makes me less cranky... sometimes.

 

[Blue Streak]

Rachel,
I used to own a 3 story 1891 Victorian in Wash Park (boy I wish I still owned it!), and I installed a 30 or 36" whole house fan in the 3 rd floor, and it was freaking amazing!
I would leave the house closed up during the day, and when the temps dropped in the evening, I would open a couple of windows on the first floor and let her rip!
It was wonderful!
Mind you, I still ended up with a window unit in the bedroom, because it just HAS to be cool.
I have to say that I kind of miss that hurricane going up the stairwell!
Enjoy it!

 

[KingGrump]

Hi Rachel,

Your top floor should be pretty close to exterior ambient temps by dawn if you are running the fan overnight. If it isn't then there is a fairly large thermo-mass that is keeping the top floor temps up. Usually it is either the roof/attic structure and/or stuff stored there. If this thermo-mass is not in direct air flow path of the fan, it will not cool rapidly and will continue to radiate stored heat into the top floor thru out the night.

 

[skibob]

We have a/c and an attic fan (older house, I assume the a/c was installed afterward). On hot days, it still gets really warm upstairs, but the basement is a meat locker. Before we go to bed, I open the upstairs windows and the basement door, and turn on the fan for a few minutes just to suck out that hot air, and suck up the cooler air from the basement. So give that a try. I don't know how your doors are configured (and I'm no expert at all on this), but I can stand in our foyer and feel the cold air moving up from the bottom level. After things cool down a bit, I seal back up and turn on the a/c, which then doesn't have to work so hard.

Don't know about your other questions.

This is what I was thinking. Try opening the downstairs only and turning fan on. It ought to be able to pull that cool air up. But if the cool basement is much cooler than outside, you might want to do that only a short time (say right before bed) because otherwise it will blow the cool air right on out of the house. It could be mroe effective to do this say right before bed and right after you get up (assuming outdoor air is at its coolest when you get up) and otherwise keep the house closed and fan off. That worked well for my cousin in the desert, but it got pretty cold at night and he still ran the AC during day.

 

[RachelV]

It's been a few weeks, and the answer just seems to be that if the nights don't get below about 65, the whole house fan alone just doesn't get things quite as cool as you'd like it to no matter what window combos we try. That's pretty rare here, though -- the fan is great overall. We also got a fan on the smaller size of the suggested range for our place, since our condo is tall and narrow, so it doesn't cool down super quick, but the fan is crazy energy efficient. I'd say we've had 2 or 3 nights over a pretty hot month where we woke up warm. Otherwise, I've been chilly and using blankets in the morning like a boss.

 

[Jerez]

Keeping the sun out, especially on south facing windows and doors can help a lot too.

This is huge. Solar screens help a lot. You can replace the screening in your existing screens yourself or spring for solar shades. We have them and you can still see the view through them, but they have a reflective silver backing that effectively keeps the heat out. We bought more than once from North Solar Screen. very good service; super easy to install. (no affiliation)

I grew up without AC and don't have it now and this works for us. Especially good if you are not in the house all day is to: Open all windows in the evening as soon as the temp is cooler outside than in. In the morning, as soon as the temps equalize, close ALL the windows. Yes, close all the windows. And the blinds, curtains of screens. Unless your house is a sieve, it will help a lot.

When we do this, it feels like coming home to an air-conditioned house.

 

[Monique]

Question!

Our A/C unit was struggling hard recently due to all the cottonwood sperm getting trapped. Apparently if it gets really bad, not only does efficiency/effectiveness suffer, but you can damage parts. A/C units around here need to have cottonwood removed yearly.

Do whole-house fans need such attention?

 

[KingGrump]

Usually only required if the exhaust vents/louvers have insect screens installed.

 

[RachelV]

Yeah, I can't see why they'd need that kind of maintenance; there's really nowhere for anything to get trapped. We just have a hole in the upstairs ceiling with a big fan on the other side of it, covered by a standard metal vent like you'd have over a central heating / cooling vent. It vents out the roof, where the vents also don't have any filters or mesh covering or anything. Part of why I love the whole house fan approach is that it's so simple.

 

[Uncle-A]

The house I grew up in had a whole house fan that worked well so when I purchased my home the first thing I did was install a whole house fan and it worked fair and that bothered me but after some research (in the days before google) I founded that if I added a fan in the attic to vent the heat out of the attic it worked better. I now have two fans in the attic to vent the heat. But my wife is not a happy with the whole house fan because it brings dust in and in the spring pollen. I have installed central AC and that works well but part of that is the two fans in the attic.