Are Attic Fans with Humidistat Effective? What Should Attic Humidistat Be Set At?

Attic fans have come to stay due largely to their performance and ability to keep attics cool and comfortable. The job of the attic fan is to reduce the temperature in the attic while keeping relative humidity at comfortable levels.

There are usually certain features and accessories that accompany an attic fan to provide some added functions for increased performance, efficiency, or convenience. A humidistat is one such component. But one may ask, what exactly does a humidistat do with an attic fan?

There has also been a lot of talk about how an attic fan with a humidistat performs.

So, are attic fans with humidistat effective? Do attic fans with a humidistat work well? Or do humidistat affect the effectiveness of attic fans in any way, positively or negatively? We’ll examine these questions shortly and tell you all there is to know on the subject.

Do I Need a Humidistat on An Attic Fan?

Yes, you do. Your attic fan needs a humidistat, especially in the winter to help fight moisture.

Here’s how it works:

A humidistat is what helps to prevent condensation in your attic. When vapor in your home rises to your attic, that’s at least 22 pints of water daily.

This can cause condensation on the roof deck which can result in mildew, mold and wood decay.

This can make your attic indoor air uncomfortable and unhealthy, while your decaying roof will cause serious damages that will require a lot of money to fix, usually reaching thousands of dollars.

The main reason you can comfortably and effectively run your attic fan during winter is that there’s a humidistat that controls the fan when relative humidity becomes too high.

The fan will draw in the dryer, cooler air from outside and remove much of the moisture which has risen from rooms and settled in the attic.

Ideally, the humidistat should have a thermocouple that can sense and identify outdoor temperature and modify the setting of the humidistat to respond accordingly automatically so you wouldn’t need to lift a finger.

Otherwise, you’d have to manually adjust the setting of your humidistat to properly regulate attic temperature and humidity.

How Does a Humidistat Work for An Attic Fan?

In winter, the outdoor temperature is relatively cooler. This is mostly due to indoor activities including cooking, showering with the bathroom heater, using your central heating system, a fireplace or any other space heating appliance.

Much of the heated air and moisture rise and find its way to the attic.

As a result of differences in temperature, this hot air condenses when it comes in contact with the roof’s cold underside. This heat in some cases can also melt roof-top snow and can cause dams. This is where an attic fan becomes necessary.

An attic fan will help to boost air circulation and ventilation, allowing some outdoor air in and removing hot air and moisture. However, you need a humidistat to set it properly so that the attic always stays within 10 degrees of outdoor temperature.

The humidistat is set at a required level so that it can automatically trigger the attic fan to come on when relative humidity exceeds that required level, which is usually between 50% and 80%.

This will help to reduce moisture in the attic, prevent the growth of mold and mildew, and safeguard the integrity of your roof.

The humidistat controls the function of the attic fan, telling it when to come on or go off, and ensuring balanced ventilation for your attic.

What Should Attic Fan Humidistat Be Set At?

The rule of thumb is to set your attic fan humidistat to between 50% and 70%. Hence, your attic fan will be triggered when the humidity level exceeds the required level.

However, this rule is not cast in stone, because some other indoor or outdoor weather conditions may cause drastic changes that will force you to adjust.

Bottom line is to ensure humidity in your attic remains at safe levels between 30% and 60% to prevent the growth of mold and mildew or support bacteria and other harmful microorganisms.

The relative humidity is different for different regions, especially in regions where weather can be extreme. By understanding your area’s weather conditions in winter, you’ll have a sound idea of how to set your humidistat.

Note that if you set your humidistat too low, the fan will run continuously and this can cause premature damage. On the other hand, if the setting is too high, ventilation will be inadequate.

What Should Attic Humidity Be in Summer?

Humidity levels should be around 30% to 40% in winter and between 40% and 50% during the summer.

This largely depends on the outdoor temperature and relative humidity. You already know that the recommended level of comfort is between 30% and 50%.

In the summer, some added moisture will help to keep things cool in your attic.

What Should Attic Humidity Be in Winter?

What you need in winter is as much warmth as you can get and humidity helps with that.

A number of factors like freezing weather, excessively hot climates, excessive rainfall, and fluctuating outdoor relative humidity can make it so hard to catch up sometimes, but having a preset humidistat is a good place to start.

By setting it at 30% to 40% in winter and 40% to 50% in summer, you should be able to enjoy good humidity levels for all seasons.

Should Attic Humidity Match Outside Humidity?

It’s perfectly fine if your attic humidity matches outdoor relative humidity. This is usually proof that the attic is properly ventilated. However, outdoor humidity may be too high, and that’s when you’d need to do something about it.

Usually, your attic humidity should be within a 10% range of the outdoor humidity, especially if the outdoor humidity is within the recommended range of 30% to 50%.

Where it is higher, you’d need more than an attic fan,  perhaps a dehumidifier, to help reduce the attic humidity.

The most important thing to note is that too much humidity in your attic can lead to a number of concerns including the growth of mold, mildew and bacteria, as well as damage to your furniture and walls.

Final Words:

We have been able to establish and show you that attic fans with humidistat are effective. A humidistat is an important component that will help to ensure humidity in your attic remains at comfortable levels.

This can be achieved by setting your attic fan humidistat at 50% to 70% so that the fan is triggered once humidity rises beyond 50%.