Whole House fans?

[Dan Schultz]

I have a 60" industrial belt-driven fan in my attic vented to outside. It'll rattle the ceiling tiles when it's running and does a great job of ventilating the WHOLE house. The problem here is southern-Indiana isn't the temperature as much as the humidity. Sometimes I'll cycle the fan on for ten minutes or so to clear the hot air in the attic and then turn it back off before it begins to draw in too much of the moist air from outside. If the humidity drops below 50% or so it does a nice job. Otherwise, it stays off most of the time.

[trseaman]

I don't know if a whole house fan would work for me either and the humidity is also a concern. I have been looking into the true attic fan like the one below, hoping to at least move the hot air out of the attic... Any thoughts on this design vs. the whole house fan??? Tim

[gwwilk]

I have a 60" industrial belt-driven fan in my attic vented to outside. It'll rattle the ceiling tiles when it's running and does a great job of ventilating the WHOLE house. The problem here is southern-Indiana isn't the temperature as much as the humidity. Sometimes I'll cycle the fan on for ten minutes or so to clear the hot air in the attic and then turn it back off before it begins to draw in too much of the moist air from outside. If the humidity drops below 50% or so it does a nice job. Otherwise, it stays off most of the time.

The most important number is Dew Point. This combines temperature and relative humidity, and gives you an excellent way to tell whether or not there is a good chance you're going to be better off opening up your home to let in the outside air. It is also an excellent predictor of outdoor exercise comfort level. Generally I won't consider opening up my home to cooler outside temperatures unless the dew point is 55 F or below because at higher dew points my heat pump works a long time and uses a lot of energy just to wring the moisture oit of the air once I turn it back on. If you don't know what the dew point value is, just step outside. If the air feels cool, chances are the dew point is favorable. But if it feels muggy, watch out.

Considerations such as these are what prompted me to install my own weather system years ago. I'm now on my fourth one, a Davis Wireless Vantage Pro2, and I find the information it provides to be invaluable. I even installed a rain guage heater so that I can record frozen precipitation amounts in the winter. Nowadays, there are quite a few weather enthusiasts such as myself, and there may even be one near you. Just go to http://www.wunderground.com/ and plug in your zip code in the upper left hand corner to see what's available. The 'sticky' in my signature contains real time data from my weather station as well as an image of the weather on my patio.

Stay cool!

[tubatooter1940]

I installed two attic fans in my present one story ranch house with thermostats that start the fans whan the attic temperature reaches 85 degrees. They really help.
My old antique house had an upstairs fan 60 inches across with a one horsepower motor installed upstairs to cool two upstairs bedrooms.
The upstairs bedroom curtains stood out 45 degrees from the open windows with the fan running and hot summer nights in July and August would find us pulling a sheet over us to keep warm.

[lgb&dtuba]

I am also concerned that during the winter the fan will act as an open window for cold air to enter the house.

Has anyone in the midwest had any experience with whole house fans? Good, bad, luke warm?

Our whole house fan has an insulated cover we place on it (from below) during the winter. Helps eliminate any heat loss.

We actually don't use it all that much. The part of the year it's actually cool enough for using it (spring) it also the same time of year that the pollen is heaviest. Sucking all that pollen into the house sets off the wife's allergies

[Philip Jensen]

I think the attic fan concept diagram posted earlier is a bit misleading . In most modern homes (those with built-in AC) the attic is already passively vented and the diagram implies this is not the case. Very common these days are whole ridge vents that allows hot air to escape, and these is coupled with soffet vents (under the roof eaves). As the hot air rises out of the ridge vent it draws in cooler air through the soffet vents (the places where wasps, etc. get into your attic) thus keeping the attic from getting too hot. In these cases I don't think a whole house fan is necessary. On slightly older houses there may be single roof vents, or possibly gable end vents (again coupled with the soffet vents).

I live in a 60 yr old house with no vents, but a gable end whole house fan. I typically will only run it in summer for a couple hours in the evening on hot days to get the heat out of the attic. As others have said, I don't like to run it when the humidity is high. If it is dry, I will run it all night, or I'll run it in the morning to cool the house and then close it up tight. I think whole house fans are most appropirate when there is no AC. Maybe in real hot locations where the passive (vs fan driven) air movemnt can't keep up they might be beneficial. I don't have experience in that kind of climate. Don't be fooled however, by the term passive. That just means YOU aren't supplying energy, and has no bearing on the amount of air moving. A well designed passive system can move A LOT of air.

As far as acting like an open window in winter, don't worry about it. As I said, most attics are already vented anyway. In fact that is desireable, at least where there is snow. You want a well insulated top floor ceiling as you don't want the attic to heat up from below and melt the snow on your roof which can lead to ice dams. Ideally you'd like your attic to be close to amibent outside air temperature all year round.

[Rick F]

As far as acting like an open window in winter, don't worry about it. As I said, most attics are already vented anyway. In fact that is desirable, at least where there is snow. You want a well insulated top floor ceiling as you don't want the attic to heat up from below and melt the snow on your roof which can lead to ice dams. Ideally you'd like your attic to be close to ambient outside air temperature all year round.

Philip is correct. You want to ventilate your attic year-round.

Roof Turbine Vents - remove in winter?
http://www.askthebuilder.com/442_Roof_T ... ents.shtml

I have 3 turbine vents on my roof and they work very well. I chose NOT to have a ridge vent installed with my new roof because there were a number of ridge vents that were blown out during recent hurricanes here in South Florida. Lose your ridge vent and there will be water in your attic -- then on your ceiling. With turbine vents, you can take them down and cap them for approaching hurricanes.

As far as "Whole House fan" goes, I don't have one. My mother-in-law in N. Georgia mountains has one. It works OK in the evening... as long as it isn't too humid outside.