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Attic fan VS A/C

post #1 of 16
6/19/10 at 3:05pm
Thread Starter 
Ok, my house has an attic fan. My dad swears by it, and always makes me turn it on when he is here (and open all the windows in the house!)

Now, I live in deep south ga. It is AT LEAST 95 here each day, heat index is usually over 100.

I keep my A/C on 73 and the house is usually comfortable in the early morning, but come afternoon the temp creeps up to about 83 and the house gets hot.

I was told a long long time ago that the attic fan uses a ton more energy than just using the a/c. But now I am conflicted because my dad says it uses less.

It doesnt seem to cool the house as much to me, and the humidity just makes everything sticky.

I'm conflicted. Help LOL
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post #2 of 16
6/19/10 at 3:44pm
Does it cool down outside at night? If so, you could use the attic fan at night and the a/c during the day. An attic fan with all the windows open isn't going to cool down the house if it's 95 outside; it's just going to make it 95 inside.

I'm in a much cooler place than you are, and I shut up all the windows in the house when the outside temperature is hotter than the inside temperature, then open up everything at night when it cools down. I don't have an attic fan or a/c though.
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post #3 of 16
6/19/10 at 3:53pm
Thread Starter 
It cools down a little at night, like mid 80's if we are lucky 70's. But the gnats and humidity at night (and mosquitos!) make it impossible to open some of the windows that dont have screens lol. I think I will just stick to the a/c. I am just scared to see my bill lol
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post #4 of 16
6/19/10 at 3:56pm
We have both, as well. We don't get to use the whole house fan enough to really make an energy comparison, but my gut feeling is that your dad is right. The problem is, though, once you have high humidity... even if the temps themselves are relatively comfortable, the attic fan (IMO) is worthless. If it is 75 out and 95% humidity, I'll close up the house and use the A/C for a few hours along with our dehumidifier before I'll use the whole house fan. Also, as we have an older home, we have had mold problems in the past that we have to keep our eye on and using the whole house fan with high humidity was a contributing factor.

I live in the midwest and for the last decade or so, we have had next to no spring or autumn seasons. I wish we did. I love the attic fan and the fresh breezes through the house.
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post #5 of 16
6/19/10 at 4:39pm
I looked into an attic fan once & although I read that it was more economical there are also supposedly dangers with it -- can cause build-up of dangerous/combustible fumes... Might want to look into that if you haven't already. But if you're only worried about the cost, why not run both? Theoretically, the attic fan would draw out excess hot air & make it easier for the a/c to fully cool the house. Despite temps in the 90's we do not use a/c at all during the day -- we keep all the doors/windows closed & use fans when necessary and can keep it pretty cool. If we open the windows it gets unbearably hot. We do use a/c at night if it's especially hot, but only because we have to keep our bedroom doors closed so with 3 of us in a tiny room it gets too uncomfortable to sleep. Otherwise it's just ceiling fans... but when we run the a/c we keep the ceiling fan on too.

What I've been trying to figure out for a while is how to keep our second floor cooler... It's currently partially finished so we don't use it much but it's a tiny cape-style house and so much heat accumulates up there despite lots of insulation etc. so I'm at a loss for how to cool it (besides a/c which I don't really want to use especially since we don't spend much time in there). Wow sorry to go off on a tangent...
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post #6 of 16
6/19/10 at 6:11pm
In high humidity areas they warn not to switch between open windows sometimes and A/C other times because the A/C works so much harder to lower the humidity if you do that. Of course, a little fresh air now and then would be good, just don't switch daily if you want a low energy bill.
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post #7 of 16
6/19/10 at 8:19pm
Thread Starter 
Yeah that is what I figured. I think once it gets to early fall and the humidity goes it will be fine to open the windows and run the attic fan. It is just too hot and humid right now, and with all the fun bugs we get in south ga it is not worth it to try and corral them out in the evening lol.

@Crunchy Mommy HOW in the heck do you not run your A/C in 90 degree temps? I guess it would also matter what the heat index is where you are...most days here it is 110-115...but holy cow I applaud you. I cannot STAND to be hot lol!
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post #8 of 16
6/19/10 at 8:52pm
Hmm I don't know the heat index, I only know the temps because they are on the signs for the banks I hate checking the weather! I would imagine we're at least a few degrees cooler here, it's very humid too, but I find with all the doors/windows closed & fans on the house maintains a comfortable temperature (70-80F). Like I said, if I open the windows, I'm miserable!! I also hate the cold so my ideal temperate is about 73F lol

ETA: We also keep the blinds closed on one side 'cause that side gets the most daytime sun. I think that helps...
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post #9 of 16
6/19/10 at 9:59pm
you should run whole house fan OR ac ... not both. whole house fan works by cooling house overnight (if temps drop to 60's) then the house slowly warms up during the day. we delay turning on ac until mid/late august, by using whole house fan.

if installing new, look up erv/hrv. a newer, better alternative to whole house fan

in GA, it may make the most sense to install window shades, upgrade attic insulation, and be comfortable with ac

nak
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post #10 of 16
6/19/10 at 10:18pm
A whole house fan and an attic fan are different things. Which do you have? Running an attic fan with the A/C would be more efficient (no need to open windows). A whole house fan is meant to be used instead of air conditioning (used with open windows).
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post #11 of 16
6/19/10 at 10:22pm
We have the whole house fan. It sucks. Really. We're in Southern Il and have terrible humidity and hot summers and the fan does nothing for it at all. We have window a/c since we have no duct work in the house. We have a one story, old, very insulated and energy efficient home.
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post #12 of 16
6/19/10 at 11:18pm
Quote:
Originally Posted by crunchy_mommy View Post
What I've been trying to figure out for a while is how to keep our second floor cooler... It's currently partially finished so we don't use it much but it's a tiny cape-style house and so much heat accumulates up there despite lots of insulation etc. so I'm at a loss for how to cool it (besides a/c which I don't really want to use especially since we don't spend much time in there). Wow sorry to go off on a tangent...
If you don't want to get an attic fan, a window fan (or fans) is a cheap alterative. Put it in an upstairs window on exhaust, and it should help pull the hot air out of the house, especially overnight.

http://www.wikihow.com/Use-Window-Fans-for-Home-Cooling
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post #13 of 16
6/20/10 at 6:17pm
We had a whole house fan in a house that we lived in as a child (north GA). We used it in spring and fall, and it did a pretty good job.

Where I live, it's pretty much AC all the time in summer, though. We consider it a really good stretch when lows get into the 70s in the middle of the night. I don't think that the house fan does a good job then.
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post #14 of 16
6/21/10 at 1:45pm
Quote:
Originally Posted by crunchy_mommy View Post
...I read that it was more economical there are also supposedly dangers with it -- can cause build-up of dangerous/combustible fumes...
If you leave the windows closed, and turn on a whole house fan, you can possible backdraft a gas water heater. (or furnace ... but that should not be used in the summer!) It is safe as long as you follow the directions and open a window.

Also, if your house is next to a truck stop or a gas grill or other combustion source, don't open that window.
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post #15 of 16
6/21/10 at 8:03pm
Thread Starter 
After reading that, it sounds more like a whole house fan. There is a knob with high/low and the vent (about 2ftx2ft) is in the hall cealing and this thing is LOUD! We turned it on last night and opened the windows when we got a torrential rain and the house temp dropped from 80 to 72 in a few mins! It was great! lol I could feel the wind whipping past me as it was sucked out the windows!

I don't see a fan from the outside of the house, and it was built in the early 70s. There isnt an actual attic either (i dont think) there is an access panel in my room, and one in the hall by that vent that comes on with the fan/vent
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post #16 of 16
6/24/10 at 2:32pm
Yes, you have a whole house fan.

If your goal is to reduce AC costs and keep the house cool, send someone up into the attic to check the insulation levels. Almost every house in my area is under insulated. There is a good link here:
http://www.ornl.gov/sci/roofs+walls/...on/ins_05.html

I prefer blown in cellulose

For the long term, install a reflective metal roof when you need a replacement, and plant shade trees.
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