How to use an attic fan effectively? Practical tips

Attic fans help to lower the temperature inside your attic by exhausting hot air from it and replacing it with the cooler air from outside. Here are some practical tips for using an attic fan effectively;

  • Run the attic fan during the hottest time of the day
  • Set the thermostat temperature to 110 degree F for better results
  • Set the humidistat level to 50% for effective removal of moisture
  • Run the attic fan in the winter too
  • Make sure that the attic has enough venting area
  • Use an attic fan of the right size
  • Service the attic fan once or twice a year

Following these tips help to increase the effectiveness as well the longevity of your attic fan. Here are these tips in detail;

how to use an attc fan effectively

Run the attic fan during the hottest time of the day

The temperature inside your attic is always higher than the temperature outside. And during summertime, this temperature difference can go up to 30 to 50 degrees depending on the area you live in. The hotter the day, the more will be this temperature difference.

As mentioned before, an attic fan replaces the hot air in the attic with the cooler air outside. So if the hottest summertime temperature outside your home is 90 degrees F then the attic temperature will be probably around 130 to 140 degree F. By replacing the hot attic air with the cooler outside air the attic fan cool the attic to around 95-100 degrees F. So in effect the fan reduces your attic temperature by 30 to 40 degrees. But at night this temperature difference will reduce to, maybe, 5 to 10 degrees even though the fan continues to consume the same amount of electricity.

So it is safe to assume that attic fans are most effective during the hottest time of the day. You can either use a timer or use the appropriate thermostat settings to restrict running the fan only during this peak time.

Set the thermostat temperature to 110 degree F for better results

Majority of the attic fan models come with thermostats. You can set a minimum temperature on these devices above which the attic fan should start running. So if you set the temperature to 100 degree F the thermostat will kickstart the attic fan once the attic temperature goes above this value. Once the temperature falls below this threshold the thermostat will turn off the fan.

image of a thermostat for attic fan

The ideal temperature to set on the thermostat depends on the area you live in, and how low you want the attic temperature to be. It is hard to say a general number for the whole of the United States however setting 110 degree F as the threshold is what is recommended by many HVAC technicians.

Set the humidistat level to 50% for effective removal of moisture

Not all attic fans come with a humidistat however some models do. You can also buy a humidistat seperately to work with your attic fan.

A humidistat helps to reduce the moisture levels in the attic by running the fan when the attic space exceeds a preset humidity level. High humidity in the attic can cause problems like mold, so using an attic fan to reduce moisture levels can dodge these risks.

A humidistat works just like a thermostat. In most cases it comes coupled to a thermostat. In this case the attic fan will start running if either the temperature or the humidity goes above the preset value.

For an attic fan, the best humidity level to be set on the humidistat is 50%. That is, if the relative humidity in the attic exceeds 50% then the attic fan will turn on. But as mentioned before, this setting depends on the area you live in. If your area has a high relative humidity it is recommended to change the humidistat setting accordingly.

Run the attic fan in the winter too

Many people are not sure if they can run their attic fans in the winter. Many considers it unnecessary since winters are cold, and keeping the attc vents open can add a load to the heating systems. But HVAC technicians always recommed having enough attic ventlation during winter. This is because during winter the attic will be warmer, and this will melt the ice on the roof but they will freeze again building ice dams which are dangerous. Running an attic fan during winter will not only reduce the temperature in the attic but also reduces the moisture levels which will otherwise cause the growth of bacteria and mold.

Image of an ice dam on roof

To run the attic fan during the winter you will have to adjust thethermostat settings accoringly.

Make sure that the attic has enough venting area

Whether you are using an attic fan or no, make sure that the attic has enough ventilation. The recommended attic exhaust ventilation is 1 sq. ft per 300 sq. ft of the attic area. But keep in mind that this is for exhaust ventilation. This value should be matched by intake vents. So in total, an attic should have a minimum venting area of 1 sq. ft per 150 sq. ft of its total area.

image of an attic

If the attic ventilation is less than this value, then using an attic fan can build negative pressure inside the attic. Since there is not enough intake ventilation the attic will pull the conditioned air from the living areas. This will ultimately lead to higher energy costs.

Use an attic fan of right size

Selecting the right size fan is very important for your attic. The size of an attic fan is measured in CFM which is a measure of the amount of air removed in a minute. A fan with 1 CFM means that it removes 1 cubic feet of air per minute.

Using an over powered fan can depressurize your attic causing structural problems as well as removing conditioned air from the house. An under powered attic fan won’t be able to provide enough attic ventilation. So make sure that the attic fan you use is the right size for your attic.

The size required for an attic fan is calculated based on the attic area. An attic fan with 700 CFM can cool an attic of 1000 sq.ft area. Here is a detailed guide on finding the right size fan for your attic.

Service the attic fan once or twice a year

Attic fans need minimum maintanance. That means they need some maintenance occassionally. Make sure you check the fan atleast once in a year. Some fans have oil ports so use them to lubricate the fan. Also check the alignment and the balancing of the fan blades and see if there are any problems with its working. Servicing the fan, even once in a year, will make sure that it runs longer.

Final thoughts

There is no one size fits all rule when it comes to using an attic fan effectively. The temperature, humidity settings and other things mentioned in this article are just a general guideline. I strongly suggest that you find the optimal settings by trial and error. It may take a few trips into the attic but it is definitely worth it.

Charles John

A novice DIYer who learns about home ventilation. I am a mechanical engineer and have a basic knowledge of HVAC systems but I learn continuously to make myself the best blogger in that space.

Latest Posts