Make-up air (MUA) is essential for maintaining balanced indoor air pressure, especially as exhaust systems—like fans, kitchen hoods, and certain appliances—remove air from your home. When too much air is removed, it can lower indoor pressure to a level that strains the function of heating equipment, especially wood-burning stoves and fireplaces. At Simcoe Muskoka Home Comfort (SMHC), we ensure that every system is designed to keep your home safe and comfortable, providing guidance on MUA requirements based on the type of appliances in your home.
Here’s a quick guide to the depressurization limits for different mechanical systems:
Manufacturers may set specific limits for their products, but these are general guidelines. In our experience at SMHC, air pressure tests are usually required by inspectors only when wood-burning appliances are installed.
For homes with wood-burning appliances, keeping depressurization in check is especially important. If the pressure drops too low, smoke, embers, or even flames can be drawn back into the home through the fireplace or stove, posing serious fire hazards and affecting air quality. To protect against this, balancing indoor air pressure is critical to ensuring safe and efficient operation of any wood-burning appliance.
At SMHC, we calculate your home’s MUA requirements based on factors like the home’s envelope tightness and the strength of large exhaust appliances, including kitchen fans and dryers. Small exhausts under 150 CFM, like bathroom fans, aren’t factored in, but dryers are larger appliances and typically count as 150 CFM each unless they’re non-ducted.
As a rule of thumb, MUA should match the maximum exhaust rate of your kitchen range hood. In most homes, natural air leakage is roughly equivalent to one dryer (150 CFM). If your home has multiple dryers, add 150 CFM for each one, plus any large exhaust fans over 150 CFM.
At SMHC, we can install MUA fans in two ways: by adding fresh air to an existing forced-air system (if compatible) or by directly ducting fresh air into the home. Each option includes a heater in the fresh air stream and a control damper to regulate airflow. If air is ducted directly into the home, it needs to be heated to at least 12°C, or mixed in with return air if used with forced-air equipment.
Our MUA systems are designed to work seamlessly with kitchen range hoods and other large exhaust appliances to maintain a safe, balanced indoor environment.
If you’re looking for solutions to keep your home safe and comfortable, contact us at Simcoe Muskoka Home Comfort to learn more about make-up air systems and how they can benefit your home.
