Why Can’t I Turn Off My Bathroom Exhaust Fan?

So you just moved into your brand new beautiful house. The home inspection is complete and everything is looking great! But after a few days you start to notice something strange – even when you try to switch it off, the bathroom exhaust fan keeps running continuously by itself. What’s up with that?

As a home inspection company, we come across this feature quite commonly these days. And we will even have clients calling about it from time to time. The good news is that your exhaust fan is not broken. It’s supposed to be like that! It all comes down to maintaining interior air quality.

Wanted: Fresh Air

In this day and age, it’s all about energy-efficient homes. Modern building codes have grown stricter, requiring new construction and add-ons to have a certain level of airtightness to minimize air leakage. This is a great step for energy efficiency! However, new homes now lack that level of “breathability” that older, draftier residences might have had. As a result, we need a way to keep the interior air fresh.

Lack of sufficient airflow and ventilation can be a real problem. It can result in excess moisture that could promote mold growth or cause moisture-related damages to the interior. It could lead to unpleasant odors, and overall unclean air. You don’t want to be breathing in stagnant air, so make sure you get that fresh oxygen flowing!

There are two main ways to achieved a consistent supply of fresh air in a newly built home: an HRV/ERV system or a continuous or timed-controlled ventilation system.

HRV and ERV Systems

An HRV (or Heat Recovery Ventilator) system is installed in the home as an addition to the furnace. It is used to expel the stale, used air from indoors and replace it with fresh air from the exterior. This apparatus is designed to extract heat from the outgoing air and add it to the incoming fresh air. A design that really helps to conserve energy!

HRV System. Image sourced from: homes.winnipegfreepress.com

An ERV (or Energy Recovery Ventilator) system does virtually the same thing as an HRV, except that it factors in heat and humidity. Depending what the in-home environment needs, this machine can either extract humidity or add humidity to incoming air. It’s especially helpful in those particularly wet climates.

As you can see, HRV and ERV systems are going to act as a set of “lungs,” providing an airtight home with fresh, breathable air.

For more info about HRV and ERV Systems, check out our blog: HRV and ERV Systems: What You Should Know

Heat Recovery Ventilator. Image sourced from: https://esupermk.live

Continuous Or Timer Controlled Exhaust Fans

If you don’t have an HRV/ERV, you’ll need a continuous or timer-controlled exhaust fan to maintain a healthy household. This is a simple fan that resembles a bathroom exhaust fan that mechanically vents air to the outside of the home. It is certainly a suitable alternative to the HRV/ERV setup. This device can usually be found on the top floor of the residence, either in a bathroom, the laundry room, or sometimes even the kitchen.

While running, the fan will typically pull air at a lower speed, around 30-50 cubic feet per minute (CFM). Then if you need it to expel excess moisture after a shower or fumes after cooking, it will allow you to turn up to a higher speed, around 50 – 110 CFM for bathrooms, 100 CFM and up for kitchens.

There are also fans that don’t run all day, but instead are programmed to run on an incremental schedule. For instance, you might find that your fan kicks on four times per day for two-hour periods. Different fans have varying programmable settings, and the best settings for your house all depend on the size of the house and power of the fan.

You may be wondering where the fresh air will come from in this configuration. As the continuous exhaust fan pulls air from the home, its suction creates a negative pressure which draws in air from leaks and cracks in the envelope. (Yes, even homes with top-notch thermal envelopes will generally have some degree of air leakage.) This, in turn, creates a consistent cycling of fresh air through the residence.

These fans are generally high quality, and energy efficient. And they are designed to be super quiet, so as not to bother the residents. In fact, some fans are so quiet that homeowners will think they aren’t working. On more than one occasion, we have had callbacks with clients claiming their bath fans won’t turn on. Upon re-inspection, we found it’s not broken, it’s just nice and quiet!

Continuous Exhaust Fans vs HRV/ERV

Even though the continuous/timer-controlled ventilation option is designed to optimize energy use, it will still likely be less energy efficient than the HRV/ERV option. While it is creating a consistent air flow through the house, it is also expelling conditioned air and replacing it with unconditioned air. That new air now needs to be heated or cooled to the desired interior temp. An action that requires – you guessed it – more energy.

On the other hand, the HRV will use the heat from the outgoing air and add it to the incoming air. The ERV takes it a step further and factors in humidity levels, as well. When air is entering the home already conditioned, that equals less work for the furnace or AC.

Because of this, newer mechanical codes are starting to phase out the continuous ventilation method. Boulder County is one such county that has implemented this update. As energy codes continue to evolve, it will be interesting to see the direction that residential air circulation will go. Will continuous exhaust fans eventually be completely phased out? Only time will tell.

Ask Your Inspector

Here at Scott Home Inspection, we love talking about houses! So if you have any questions or thoughts about in-home ventilation (or any other home-related topic), feel free to reach out through our “Ask Your Inspector” program.

We have been offering inspection services to the CO Front Range for over 18 years. And it is always our goal to provide our clients with the most professional, reliable, and trustworthy services. If you are in need of a Colorado home inspection, we hope that you will consider Team Scott! For more information, you can visit us online. Or you can contact us to book your inspection today!