How Much Cfm Do I Need For Attic Fan

Select if your roof is more flat of peaked.

How much cfm do i need for attic fan.

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. There is nothing wrong with whole house fans. That s why my article give advice on sizing installing and using these fans. These power attic fans can actually create more problems than they solve.

Ventilation rate of 10 air changes per hour. For heating and air conditioning airflow or for other exhaust fan situations see our airflow calculator. Ft of attic space for example 20 x 50 to be effective. Any whole house fan that you buy should have this figure listed somewhere on the packaging.

Then click on calculate. Ft home would need a 3000 cfm rated fan to achieve the 1 5 cfm per sq. However a constant flow of air is required to remove the heat that is radiating from your rooms walls ceiling and attic. Use the chart below as an attic vent fan cfm calculator.

The same home would need a 4000 cfm rated fan to achieve the 2 0 cfm per sq. 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. Sizing for large bathrooms for bathrooms over 100 square feet exhaust fans can be sized according to the number of fixtures in the room. 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.

What s wrong with a large cfm attic power vent fan say 1400 1600 cfm and a set of ceiling shutters a. Ft of living space. To facilitate faster air exchange would necessitate choosing a fan with a higher cfm. This is done because you need one square foot of ventilation area for every 750 cfm that your fan can push.

Attic x 0 7 700 cfm minimum fan rating. Proceed to step 2 and use the chart to determine the size and number of solar powered attic ventilation fans required to achieve a min. 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. 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.

Now take that number and divide it by 750. Add an additional 20 cfm x 1 20 if you have a steep roof and 15 cfm x 1 15 for a dark roof. For open blade fans see our ceiling fan calculator. Then enter the height at the highest point.

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