What is Makeup Air?

What is Make-up Air?

Make-up air refers to the replacement air that is brought into a building to compensate for air that is exhausted by ventilation systems or other processes. In a well-designed building, make-up air ensures that there is a balanced airflow, maintaining indoor air quality and comfort while preventing negative pressure conditions.

What is the Purpose?

The primary purpose of make-up air is to replace the air that is exhausted from the building by mechanical ventilation systems, kitchen hoods, bathroom exhaust fans, clothes dryers, and other appliances. Without adequate make-up air, excessive negative pressure can develop within the building, which can cause a range of issues such as discomfort for occupants, inefficient operation of exhaust systems, and even back-drafting of combustion appliances.

How it Works

Make-up air can be introduced into the building through various sources, including outdoor air intakes, dedicated make-up air units, or natural ventilation openings such as windows or vents. The source of make-up air depends on factors such as the building's design, climate, and ventilation requirements.

Where it Goes

Once introduced into the building, make-up air is distributed throughout the space to ensure even airflow and ventilation. This may involve the use of HVAC systems, ductwork, diffusers, grilles, or other air distribution devices to deliver the fresh air to occupied areas.

Control

Make-up air systems are often equipped with controls to regulate the flow of air based on factors such as occupancy levels, indoor air quality, temperature, and humidity. This helps optimize energy efficiency while ensuring adequate ventilation and comfort for building occupants.

Energy Efficiency

Nowadays, energy efficient homes have become the new normal. Energy efficiency includes sealing all places where air can get in, but making it hard for air to enter presents some challenges when it comes to ventilating exhaust.

When an exhaust appliance removes air from your house, an equal volume of air must enter to eliminate the negative pressure. In older homes, the leaks and drafts present would supply any necessary makeup air. In newer or more energy-efficient homes, there aren’t enough random air leaks around windows, doors, and mud sills to make up the exhaust air. Makeup air is then pulled through water-heater vents, clothes dryer vents, or down wood-burning chimneys, a phenomenon called backdrafting. Due to the gases from appliances, backdrafting can be dangerous and needs to be prevented. To do so a make-up air system must be installed.

When is Make-up Air Required?

Whether or not make-up air is required for your kitchen depends greatly on the size of your home, how air-tight it is, the power of your range hood and if you have a gas range or any other combustible appliances. If you have a gas range and/or your range hood is higher than 600 CFM then in a lot of cases make-up air is required. In some cases, anything over 400 CFM will require make-up air.

We recommend getting a professional opinion from someone in the HVAC industry if you are not sure if you need make-up air or not. We also recommend researching your local building codes as some cities require make-up air for any range hood that meets a certain CFM threshold.