If the fan to which you are referring is a large attic fan that acts as an exhaust, drawing outside air into the house through the windows on the living levels, then I would not install one if you are an allergy sufferer or a clean freak. In addition to air, these fans also draw dust and allergens (although allergens are possibly less of an issue in Arizona than in other states) into the house.

What is the interface between the house and the attic? A problem with whole house fans is that that ceiling opening (often louvered) can allow air leakage from the attic into the house, cold in winter and hot in summer.

If your electricity cost is reasonable or at least affordable for you, I would use your AC to cool the house until it's cool enough outside to open the windows and forget the attic fan. Make sure the attic has enough passive ventilation all the same.

We live in an old house with a newer addition. We installed two smaller whole house fans (Quiet Cool brand), rather than one large one. You can hear them running, but it is really not much more noticeable than when the ac or heat are on. I used to feel like the heat was trapped in the house as it would take a long time to cool off. The fans pull the cool air in and flush the attic. During high pollen season, I do not use the fans and really miss it. My fans have been on this morning for 2 hours and I dropped the temperature in my house by 5 degrees, from 76 to 71. It is in the high 60s outside. Also, I really do not notice more dust in the house when I am using them. We put the fans on a timer. My husband was a skeptic about installing them, but would do it again now that we have them.

We love our whole house fan. The temperature difference in a day can be extreme and except for the hottest days in the summer we run it all night instead of the air conditioner. It is also so much more pleasant than the air conditioner cycling on and off.

We had a whole house fan in our old house but when my parents installed central AC, they had it taken out. Many times I heard them say that was a mistake, especially on days in seasons when it was cooler outside then inside. If I ever build a house, I will include a deep, screened-in porch on the side or back of the dwelling, and of course, a whole house fan!

I'd not want to live in house without a whole house fan. Having done the seal up the house and let the HVAC system control everything, we much prefer the much fresher air from open windows. No ventilator can come close.

Our first choice for HVAC is open windows w/ a natural breeze, second is turning on the whole house fan. Only when absolutely necessary will we use the HVAC system and even then it's not unusual for us to open windows on warmer (like anything over about 20°f) winter days for a bit of extra fresh air.

BTW, several doctors I know believe that many people's allergies are caused by too little exposure to our natural environment and a lessening of our natural immunities.

Can I ask if anyone installed your whole fan on a flat roof...any particular brand/model you'd recommend (or ones to stay away from)? We're building in northern AZ and would like to include it while building. Thanks in advance for any info.

Tamarack (good company) has a couple that will work on a flat roof but they are only 800cfm so you'd likely need a few of them. They have several that can exhaust out of a side wall though which is what we are doing.

Another option might be a roof mounted commercial blower. Greenheck has some but there are other more affordable options. Have you asked your HVAC folks what they'd recommend?