House ventilation 101: A homeowner’s guide to continuous running exhaust fans

Why ventilate my home? 

While CEE is dedicated to helping people make their homes more energy efficient, we also want people to live in homes that are safe, healthy and that have good indoor air quality.

According to the Minnesota Department of Commerce’s Division of Energy Resources, “Good indoor air quality is important for a healthy home. Proper and efficient ventilation removes unhealthy contaminants (such as smoke from cooking, moisture from bathing, or combustion products from heating systems) and brings fresh air into the living spaces.” 

Homes without proper ventilation can experience a variety of problems with indoor moisture, odors, and pollutants, which can lead to mold growth or physical damage to the home over time. To reduce those risks, moisture from cooking and bathing needs to be removed. Without adequate ventilation, contaminants like formaldehyde and volatile organic compounds (VOCs) can accumulate and may cause health problems. Too little ventilation can also allow unpleasant odors to linger.

Typically, newer or recently air-sealed homes have less natural ventilation from things like gaps and openings around doors, windows, and the home’s foundation, which means pollutants aren’t regularly flushed out of the home. The issue isn’t that these homes are too “tight” — it’s that they are not “breathing” properly. Mechanical ventilation, in the form of exhaust fans or air exchangers, allows homeowners to better control the breathability of their home.

When should I add ventilation to my home? 

In existing homes, installing continuous bath fans is generally the most cost-effective way to add mechanical ventilation. Many people also add ventilation during an insulation or air sealing project because the work will restrict how a home breathes. Some cities require HVAC contractors to install fans, but others allow installation contractors to install them, so be sure to speak to your contractor about your options. If you'd like help determining if ventilation is the right solution for your home, consider having an energy audit. Your utilities may provide this service. 

What type of ventilation do you recommend?

For many existing homes, exhaust systems are an effective way to ventilate. Exhaust systems remove air from your home, while balanced systems both remove air and bring in fresh air from outside.

CEE recommends installing an ENERGY STAR-rated bathroom exhaust fan or kitchen range hood that is rated for quiet and continuous operation. These fans typically have two speeds, which are controlled by a motion sensor or switch. The continuous or low speed setting is typically 30–50 cubic feet per minute (CFM). Higher speeds are used when bathing (50–110 CFM) or cooking (more than 100 CFM).

The installer can set the fan speed based on factors like the number of occupants and the home's tightness, which ensures that moisture and indoor air pollutants don't build up over time. Fans can usually be adjusted by occupants by removing the fan grate and adjusting the dials inside.

How do I adjust the fan settings?

Typically, there will be one dial for adjusting the speed, or CFM, and one to set the time the fan will remain on after being triggered by a motion or wall switch. You can increase the speed of the fan when it is humid inside or when there are odors in the home. In a bathroom, the fan may stay on longer if it is unable to keep the room dry. 

Where should I install continuous ventilation?

We recommend installing a continuous ventilation fan in the most frequently used bathroom in the top floor of the home, replacing any existing fan in the room. If a home’s structure doesn’t allow for installation of such a fan in the bathroom, sometimes a kitchen range hood rated for continuous use is an option. In most cases, one continuously ventilating fan — either in the bathroom or kitchen — is enough.

Continuous ventilation fans use motors to take in air from the home and blow it outside. The fan pulls air from small leaks or cracks in the home or the combustion air intake, which is flexible ductwork that goes into your mechanical room to keep your mechanicals functioning properly. That air is then pushed outside. In a balanced system, fresh air is pulled inside to replace it.

How much does it cost to install? 

Costs for installing an ENERY STAR continuous operating fan can vary widely. This will depend on your home, the fan chosen, and your location. In some cities, fans must be installed by an HVAC contractor. In other places, installation contractors can install them. The installer, plus the permits required for the job, can impact costs. We recommend speaking to your city permits department or contractor for more details. If you've gotten an energy audit, you may contact your energy advisor for personal guidance, too.

How much will it cost to run the fan all the time? 

We recommend running the fan continuously, 24/7. Continuous operation allows the fan to be set to a lower, quieter speed. It typically costs $15–$20 per year in electricity to operate the fan this way. Additionally, the continuous fan will exhaust a very small amount of already heated or cooled air from the home. 

While this may sound counterproductive at first, adding ventilation is overall very beneficial. It goes a long way toward preventing structural damage to your home and health issues for you and your family, both of which would cost more than adding a ventilation system.

If you add a continuous fan as a part of an insulation project, know that the savings from air sealing and insulation work are typically much greater than the small amount of air the fan removes from the home. 

What maintenance is required?

Most fans should be cleaned at least once a year. Both the fan grill and body should be cleaned. Specific guidance on when and how to clean your fan will be determined by the model you have, and should be explained when the fan is installed. If you need a refresher, the manufacturer may have more information on your specific fan.

Can I leave my current fan switched to “on” instead? 

It's not a good idea to leave your current fan on all the time instead of installing a new continuously running run, because the motors are not designed to be left on all the time and may break down. Once this happens, you would need to replace the fan anyway. Additionally, older fans are louder than continuous rated fans, so installing a new fan may help your air quality and the noise levels in your home.

How do I get started?

If you don't know much about your home's current ventilation, an energy audit could be a good place to start gathering information. Typically, utilities provide these to customers at a low cost to help them understand their home's energy use. In many audits, ventilation is checked as part of the tests of a home's air tightness. If you've had an energy audit or are planning a ventilation project, you can speak to a contractor about your options.