how economical is an attic fan?

Answer 1

For the cost of running one electric motor it can keep most houses as cool at night as an air conditioner does. Of course there are some hot nights it will not do that because the outside air coming in as just as hot. However if you run it at dusk even on those nights or when you first come home from work , it will at least get enough super-hot air out of the attic that the air conditioner will have less work to do resulting in savings right there.

Answer 2

Pretty open ended question, not sure if you are talking about the fan's electrical usage or it's cooling efficiency.

As for the electrical efficiency, that will depend on
1) the horsepower rating of the motor
2) the pitch of the fan blades, over which you have no control
3) the adequacy of the ventilation system from your attic to the outside; if there is insufficient venting, your attic will be pressurized and the fan will have to work harder!
4) and the voltage supply required by the motor. A 240 volt motor will cost you less to run. Some have dual voltage hookups for either 120 or 240 volts.

Cooling efficiency? Fan noise aside, in the Southeast where I am, they do a good job in spring and early summer. After about mid-June, they just suck the hot air into the house. The air is definitely moving, but leaves a lot to be desired. I spent one summer with our attic fan with temps hitting low 90's. That fall I had 16" of extra attic insulation added (yes, I covered over the attic fan!) and had a high efficiency heat pump installed. All was INSPECTED and financed through my local TVA electrical co-op at ZERO interest and 5 years to pay. That was 14 years ago and we have been enjoying the central heat and air as well as VERY LOW electrical costs every month. If you're south of the Mason-Dixon line, you cannot beat the efficiency of a properly installed heat pump. North of the line....you're stuck with gas or oil, I guess.

Answer 3

Adds about 5 years to the life of roofing shingles