Proper attic ventilation consists of a balance between air intake at your eaves soffits or fascias and air exhaust at or near your roof ridge.
How much attic fan do i need.
If you need 6 000 cfm of air flow through your house divide 6 000 by 750 to get a minimum 8 square feet of.
An attic fan is installed on the slanted side of your roof or on one of the gable sides of your attic.
These fans are designed to remove excess heat from your attic which in theory is supposed to lessen the load on the air conditioning in your home.
You need a minimum of 1 square foot of attic air venting for each 750 cfm of air flow.
Your soffit ventilation actually needs to be considerably more than 336 net square inches to supply a 700 cfm fan system or the fan is going to pull the air it needs through unsealed holes and gaps in the attic floor from the conditioned living space.
Generally speaking you need a ratio of 1 300 where for every 300 square feet of ceiling space you need 1 square foot of attic ventilation.
I had my attic floor sealed and a good amount of blown in insulation.
Attic fans are cheap compared to whole house fans.
Without exception you should talk to a professional to determine what your home requires.
Attic fans exhaust hot air from your attic to the outside.
Federal housing authority recommends a minimum of at least 1 square foot of attic ventilation evenly split between intake and exhaust for every 300 square feet of attic floor space.
Yet i still see the attic temperature reach 145 degrees.
All you need to know about attic ventilation.
How an attic fan works.
Attic x 0 7 700 cfm minimum fan rating add an additional 20 cfm x 1 20 if you have a steep roof and 15 cfm x 1 15 for a dark roof.
Without this open space the fans will not move much air.
Whole house fans need windows and doors open and attic fans need lots of soffit vents to suck cooler outdoor air up into the hot attic.
When i last had a new roof installed a few years ago i calculated the soffit intake area i d need for the ridge vent specs.
All of that is in place.
It might cost you approximately 300 600 for purchase and up to 550 when you include labor.
A 1500 square feet attic would cost 70 with additional humidistat costing 15.
That said air resistance and interference such as vent grates reduces the area of true ventilation.
