Do attic fans really work? This is a much-debated topic than I thought. There are HVACs and builders on one side that argues they are much needed, for every home, and then there are those (also in the construction/ air-conditioning industry) who argue they do worse than good.
Who is correct?
Here is a never-ending debate on this topic – (Please don’t click it yet, check my next paragraph) https://www.energyvanguard.com/blog/75600/The-1-Reason-Power-Attic-Ventilators-Don-t-Help (Make sure you read the comments)
What I am going to write here is the condensed version of all those arguments, so I think you are better off reading this article first and checking that link later.
The main arguments against the installation of powered attic fans (PAV) are;
- They do not help much in cooling the house
- The cooling achieved by attic fans is majorly due to the ‘makeup air’ ie, the cold air they suck from your living area.
- They are not cost-effective.
- More is saved by improving the insulation of the ceiling
Let’s check those points in detail;
Myth 1. Attic fans do not help much in cooling the house
The logic here is that the majority of the heat in the attic, and inside the house is due to radiation from the hot roof, and it is impossible to remove radiant heat through air circulation.
Had this argument been correct then the air in the attic wouldn’t be hot at all, only the roof deck and the other stuff like insulation, framing etc would be hot. Though air is a bad conductor it gets heated by convection ie, the hot air near the roof deck and the insulations will circulate spreading heat throughout the attic.
So, does removing that hot air cool down the attic? Just imagine your car parked in the hot sun. It will be sizzling hot but when you open the doors/windows for a few minutes its interior will cool down. Your attic is just like that.
That being said, this argument of radiating heat is not completely false either! It is NOT the hot air in the attic that heats up your living room. The ceiling absorbs radiant heat from the roof deck and transfers it down to your living areas. So removing the hot air in itself is not the solution.
Doesn’t that mean an attic fan is useless?
Actually no. When there is circulation of colder air from the outside the radiant heat absorbed by the insulations and other materials there will be removed via convection. So this reduces the amount of heat transferred into the house.
Myth 2. The cooling achieved by attic fans is by makeup air
I can’t say this is completely wrong. No ceiling is 100% leak-proof, so an attic fan will surely suck some of your cooled air. This happens when there is negative pressure in the attic.
By providing proper roof vents, this can be avoided but not to 100%. HVI advises a minimum of 386 square inches of soffit ventilation for an attic fan of 700CFM.
Myth 3. Attic fans are not cost-effective
One of the many attractions of buying attic fans is that in time they will cover up their costs. Unfortunately, that may not be true for everyone.
And to tell the truth, not everyone cares whether they are cost-effective;
People collect a lot of stuff, and many keep them in their attic. In hot areas like Texas and Nevada, the attic temperature rises to 150 degrees. Just imagine you going there to collect things. So in most cases, it is a matter of convenience.
And if you are using a solar attic fan it further reduces your electricity bills.
Attic fans can be cost-effective in some houses and it may not be in some. Its performance and cost-effectiveness depends on a lot of things and varies from house to house so you kind of requires an ‘attic audit’.
Myth 4: More on air conditioning can be saved by improving the ceiling insulation
This is actually true. If you can invest in bettering the heat insulations of your home that is more cost-effective than using an attic fan. But you will need an attic fan anyway if you are using the attic for storage.
So are attic fans good or bad?
There are cases when an attic fan is not the best solution but in most cases using attic fans is a good choice.
How to know if you need an attic fan?
An attic fan increases the air circulation through the roof, that’s what it does. Any benefits projected by those who support attic fans are the result of this increased air circulation.
If your ceiling has good heat insulation (R19 or above) I won’t say an attic fan is the best idea economically.
But you need an attic fan if the R rating is less than 14.
If your home doesn’t have air conditioning then using a whole house fan is far better than an attic fan.