Building 3500 sf house in N Arizona where temp ranges in summer 60 degrees night 100 day. House has flat roof with 8 different roof trusses. Would a whole house fan make sense in this application? Do I need one for each roof or can I put large one in biggest roof? If so are they noisy? Any recommendations on products? I would appreciate any insight here.
KennyZ
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Replies
Do you mean a whole house fan as opposed to A/C, or do you mean an attic vent fan in addition to it?
Personally, 100 is too hot for just a house fan. I'd add the attic fan, especially if you can get it to cool the area the A/C unit/ducting is in.
I live north of you in Idaho and love my whole house fan. I got a free squirrel-cage furnace fan from a HVAC dealer and installed it above the ceiling in a common hallway. Self-closing dampers and a 3-speed switch is all that you see from inside the hall. I built an insulated plywood box around the fan up in the attic.
The big advantage of a WHF is that it forces out hot attic air and brings in cool air through any open windows (only works summer nights here in the intermountian region where nighttime temps drop 40-50 degrees).
This type of fan is a bit noisy on high speed.
Have a source for those dampers?
I put a 3500-cfm swamper in my parents house in Boulder City. It entered through the garage, and ducted through blind vents with dampers in the upstairs rooms to vent into the attic, and put a 3500-cfm fan to pull out the attic air.
The water and power are on the same bill there. The folks were traveling that summer. Dad called in a dither, because the water and power bill had dropped to less than a fourth of what it was the year before. He was certain, that I was not watering his yard. The swamper had cut the power use by 85%, and except for a few days in the August monsoon season, it never seemed very humid in the house.
The pay off on the swamper and fan were one summer. That was in 79, and Mom is still using them.
Make sure you have lots of attic venting. I added four 12" turbines and when I turn on our belt drive whole house fan, they spin up a storm.... With our high Humidity, I didn't use it much and the ceiling shutter is still sealed.
A whole house fan would help you IF:
You Have Low humidity
Put it on a timer so it cuts off in the early morning hours. Once your house is cool, use your room ceiling fan to stir the air in the bedroom.
Place you whole house fan in the ceiling of a laundry room where there's a distance from sleeping areas because the metal shutters will rattle as it runs and you'll need to cover the shutter for winter time to prevent heat loss.
Whole house fans are good to pull cool air inside, but 80 degrees is about the cutoff temp for comfort. I ran ours on a timer and after the house was cool, I discovered a well insulated home will rise in temperature about 1 degree per hour, so closing all the windows after the the air and the heatsink furniture is cool will keep you cool. This is the Major Perk of the 60 degrees at night and 100 degree days. You might not have to turn on your HVAC until 3:00 or 4:00 pm.
You have to open some windows to let air in, so be sure to put window blocks/locks on the sash rails to limit their opening by the bad guys. You'll have to dust a little more often as the incoming air will bring in the stuff that settles out of the daytime air.
Some whole house fans are two speed which helps in limiting how many windows you have to open on High vs Low speed. Just remember air is being pulled out, so it's got to come in from somewhere. Too few windows open can be an issue. If you are on Pier and Beam, stuffy foundation air might be pulled in, furnace and hot water heaters vents become air INLETS instead of Flu Venting OUTLETS, and if you have a fireplace, you'll have to be sure the damper or fireplace doors seal, or part of the house will smell like ashes... It's an Even Stronger smell with wet ashes from a chimney that doesn't have a raincover....
Bill
I'm in the second house where I've installed a whole house attic fan. We don't get to 100 often, but 90 regularly. We don't typically run the a/c more than a couple of weeks each year. My rule is when the overnight low is 70 degrees or dew point is 70 degrees.
Thanks for sharing. Does you fan exhaust from conditioned space into the attic or is it vented thru the attic and exhaust on the roof? If into the attic, do you have a large attic or a tiny space like on my flat roofed house. Is the fan noisy?
Stay cook.
Kennyz
There are two kinds of whole-house fans. There are the old-school ones, which are little more than a big fan and a set of louvers. They move a lot of air from the house into the attic, are relatively inexpensive, and really loud. They are also rarely insulated, though people often put covers over them to insulate them during heating season.
There are some higher tech ones made by Tamarak and AirScape. These don't move as much air, but are much quieter and have motorized insulated dampers.
I put an AirScape 1.7 in my house last spring, and have been really happy with it - I can easily get the 80 degree air out and the 55 degree air in.
As others have noted, you have an opportunity to use a swamp cooler in your house because you have low humidity.
There's another "old school" way to install a WHF. Louvers in the upstair's hall ceiling ducted to the nearest gable end wall where the fan is installed, taking the hot air directly outside.