How Much Cfm Do I Need For Attic Fan

Attic vent fans are commonly rated from 800 to 1 600 cfm making one fans suitable for attics of up to around 2 200 square feet.

How much cfm do i need for attic fan.

Ft home would need a 3000 cfm rated fan to achieve the 1 5 cfm per sq. That s why my article give advice on sizing installing and using these fans. Attic x 0 7 700 cfm minimum fan rating. So if your fan is rated at 1500 cfm you will need about two feet of totally open space in your attic.

Add an additional 20 cfm x 1 20 if you have a steep roof and 15 cfm x 1 15 for a dark roof. Ft of living space. These power attic fans can actually create more problems than they solve. What s wrong with a large cfm attic power vent fan say 1400 1600 cfm and a set of ceiling shutters a.

For heating and air conditioning airflow or for other exhaust fan situations see our airflow calculator. Some of these fans can pull as much as 1500cfm of air and if there is not enough soffit gable or ridge vents the fan. Enter the length and width of your attic or ceiling crawl space. Now take that number and divide it by 750.

Then enter the height at the highest point. Ft of attic space for example 20 x 50 to be effective. This is done because you need one square foot of ventilation area for every 750 cfm that your fan can push. Ventilation rate of 10 air changes per hour.

The minimum allowed fan size is 50 cfm so if your bathroom is for example only 42 square feet you still need a 50 cfm fan. Use the chart below as an attic vent fan cfm calculator. Another way to look at this is to calculate how many air exchanges are performed in an hour for a fan with a certain cfm. Then click on calculate.

The same home would need a 4000 cfm rated fan to achieve the 2 0 cfm per sq. According to the home ventilating institute hvi powered attic ventilators need to move a minimum of 700 cubic feet per minute cfm for 1 000 sq. For open blade fans see our ceiling fan calculator. There is nothing wrong with whole house fans.

However a constant flow of air is required to remove the heat that is radiating from your rooms walls ceiling and attic. I recommend that you do not install a power attic fan as studies have shown that the fans actually use more energy than they save by cooling the attic. Any whole house fan that you buy should have this figure listed somewhere on the packaging. To facilitate faster air exchange would necessitate choosing a fan with a higher cfm.

So as another example moving to a 2500 cfm fan would cut the air exchange time to roughly 7 minutes 17 600 2500.