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
- Use recommended thermostat settings
- 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;
Table of Contents
1. 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 cools 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.
2. Use recommended thermostat settings
The 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. For example, if you set the temperature to 100 degrees Fahrenheit, 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.
The most recommended temperature setting for an attic fan in summer is from 90 to 110 degrees Fahrenheit. Ideally, the temperature setting should be equal to the outside temperature, and this is the thermostat setting most HVAC technicians to recommend.
This temperature set on the thermostat depends on the area you live in, and how low you want the attic temperature to be. If you want to start the attic fan at a lower temperature, change the thermostat setting accordingly, however for best results it should be on par with the outside temperature.
3. 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 separately 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 with 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.
4. Run the attic fan in the winter too
Many people are not sure if they can run their attic fans in the winter. Many consider it unnecessary since winters are cold, and keeping the attic vents open can add a load to the heating systems. But HVAC technicians always recommend having enough attic ventilation 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.
To run the attic fan during the winter you will have to adjust the thermostat settings accordingly.
5. 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.
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.
6. Use an attic fan of the 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 foot 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 underpowered 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.
7. Service the attic fan once or twice a year
Attic fans need minimum maintenance. That means they need some maintenance occasionally. Make sure you check the fan at least once 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 their working. Servicing the fan, even once a year will make sure that it runs longer.
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 general guidelines. 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.