I have gable fans and I thought I'd do a little check to see how much they saveMy rough calculations actually turn out to be a net loss with 1800 sq ft of R-30 insulation and a 500W fan-even if the attic gets up to 130F or more without it! The energy to run the fan just didn't add up to savings against 13 SEER coolingBy my calculation, a 500W fan needs to reduce the cooling load by 6500 BTU to pay off (again, 13 SEER efficiency)Googling failed to provide me with information supporting the theoryAnybody out there know the facts or where to find them?
Leaving them in either HP sauce overnight or Coca Cola works
It depends on your house and areaPowered ventilation should only be used when the attic vs conditioned space temperature gets highIf the air temperature is high enough to use AC then the attic can get very hotMoving that hot air out and replacing it with cooler air should reduce the cooling costHowever the building and how it is used makes a huge differenceThe attic fan pushes out hot air or sucks in cooler airBut if the attic is not well vented or if storage uses block vents then bad air flow can happen In the case of a fan set to suck in cooler air, the attic can pressurize and actually push attic dust back into the living spaceIn the case of a fan set to push out hot air, the attic can depressurize and suck the air out of the living spaceThis looses cool air and sucks hot air in from underneath the houseit can also create a negative pressure on combustion appliancesThis can cause CO gas in the house or a back-draft fireGood thing is that most houses leak so bad that the last hazards are not all that likelyBut it is your lifeSo look at where the air comes from and goes to.
