What is Makeup Air, and Why Is It Important? Posted on August 17, 2022 If you’ve ever been to the rooftop of a residential or commercial building, you may have noticed these giant machines sitting on the deck. While most people think of them as generators or machinery for the elevators, they are most likely the make up air units for the building. But what is make up air, and why do buildings need them? In this article, we discuss the concept of makeup air, its effects, and why it matters. What is Makeup Air? In all sealed buildings, the air pressure inside tends to be lower than the outside. This is caused by appliances and machines that push or pull air, or it can also be due to the building’s layout. Whatever the case, it creates a pressure air imbalance. This means that outside air tends to get sucked into the building, which can have negative effects for the building’s occupants as well as the structure itself. This is where make up air comes in. Make up air (or makeup air) is exactly what the name suggests: it is controlled outside air that replaces the air exhausted from inside. Appliances that push or pull air, such as fans, range hoods, and clothes dryers, tend to depressurize the interior. Rather than letting outside air get sucked in every time someone opens a door or window, makeup air is the controlled and filtered air that replaces the exhausted air inside. What Happens if You Don’t Control the Outside Air? Unless properly channeled and filtered, makeup air can cause a number of detrimental effects to both the occupants of the building, as well as the building itself. These include: Poor air quality External air sources can consist of smog, toxins, allergens, and environmental pollutants. These can degrade the air quality indoors and cause long-term health problems. Noxious gasses, fumes and carbon monoxide from the fireplace or furnaces may also be trapped inside the house instead of being vented. Unwanted drafts Since air follows the path of least resistance, it can cause uncomfortable drafts even in seemingly sealed rooms. This will be more noticeable in older or poorly sealed structures. Structural damage Outside air can seep in through gaps in doors, windows, walls, ceiling and the building’s foundation. Over time it causes premature wear and tear in weatherstripping and structural support. Higher costs Makeup air can cause havoc with the interior climate. The thermostat may struggle to maintain room temperature due to air infiltration , leading to larger bills. It can also take a toll on air conditioners and heaters, forcing them to work harder to maintain the desired room temperature. This leads to more frequent breakdowns and lower operational lifespan. Why is Make up Air Important? ✔️ Better Indoor Air Quality Makeup air is properly screened and filtered for environmental pollutants, toxins, and allergens, ensuring safe indoor air quality (IAQ). In fact, OSHA has guidelines on what the proper IAQ should be for commercial and institutional buildings. ✔️ Comfort A constant flow of outside air can lead to noticeable drafts or warmer / chillier room temperature. A makeup air unit eliminates drafts and cold spots. ✔️ Lower utility costs Makeup air units ensure that indoor temperatures remain constant and less prone to wild temperature fluctuations caused by external air. ✔️ More efficient HVAC Many units condition incoming makeup air so that heaters and air conditioners don’t need to work as hard to maintain the indoor climate. This results in less wear and tear, lower filter clogging, and longer operating lives. Where are Makeup Air Systems Required? Residential homes Tightly sealed houses can result in unequal pressure, even when just opening doors. Some powerful rangehoods can cause negative air pressure in the kitchen Other household appliances can suck air out of the house, causing unfiltered air to seep in and exacerbate gaps, holes or cracks in the exterior walls and in weatherstripping. Even a bathroom exhaust fan can cause air imbalances. Dormitories and condominiums Multiple units, entrances and hallways tend to destabilize pressure equilibrium Lack of makeup air can result in odors and cooking fumes being noticeable from adjacent units Hotels and resorts There are professional standards regarding minimum ventilation for motels, hotels, and resorts. These cover air shifts for different areas of the building, from the lobby and hotel room to multipurpose function halls. Industrial structures Makeup air systems ensure adequate ventilation for workers The system also removes industrial byproducts like contaminants and fumes Commercial kitchens An industrial makeup air unit is required for restaurants and commercial kitchens to ensure proper exhaust and ventilation for kitchen workers. Healthcare facilities The spread of infectious diseases is prevented through clinical-grade filtering a and multi-stage microbial treatment Since patients have more delicate requirements, medical makeup air systems must also adhere to strict regulation regarding humidity, temperature, and minimum air changes per hour. Educational institutions There are specific guidelines covering classrooms for different age groups. Some areas of the school like science labs and metal or woodworking shops also require more robust makeup air to prevent fume buildup. Office and corporate spaces Makeup air is essential for office spaces, considering that employees spend at least 8 hours per weekday sharing the same interior space. Air change standards depend on the size, occupancy and layout of the office. Make up Air vs Regular Ventilation: What’s the Difference? A standard ventilation fan is designed to bring in outside air as-is without any heating or tempering. This makes them useful for areas with temperate climates year-round. In contrast, a makeup air system heats or tempers the outside air before circulating it indoors. This makes them more suitable for areas that experience different seasons. It also allows the indoor heating or cooling system to work more efficiently. While simple ventilation fans can provide fresh air in temperate climates, using fans during cold winters or hot summers can create uncomfortable temperatures. Make up air systems ensure the replacement air is properly conditioned and filtered for better comfort. Makeup Air FAQ Do Residential Houses Need Make Up Air? If you have a small kitchen or a powerful rangehood, you may need make up air. The power of rangehoods are measured in cubic feet per minute (CFM), which refers to the amount of air they can suck in one minute. Hoods with a rating of 1,200 CFM or higher may be powerful enough to create an air pressure imbalance – that is, they pull too much inside air out. This lowers the indoor air pressure, causing outside air to be sucked in. The more powerful your rangehood, the more likely you need make up air. Even if you don’t have a big hood, you may need make up air if you have a small kitchen or it’s not as well ventilated. Smaller kitchens have less air. This tends to create an air pressure imbalance every time you use the hood. The age of the home and quality of construction also make a big impact on whether or not make up air is needed. A modern home with spray foam and other good air sealing techniques is likely to require fresh air to be brought in from outside to prevent the air in the home from getting stale. Most older, more loosely built homes do not have the same need. Do Condos or Apartments Need Make Up Air? Some residential building codes require make up air. This is usually the case for residential units with rangehoods over 600 CFM, since apartments and condo units typically have small kitchens where the air can be quickly exhausted. ASHRAE Standard 62.2 also specifies ventilation and IAQ standards for dwelling units with non-transient occupants, which applies to apartments and condominium units. Do Commercial and Industrial Buildings Need Make Up Air? Yes. ANSI/ASHRAE Standard 62.1 specifies the minimum ventilation rates and other measures intended to provide good indoor air quality (IAQ). The standard is often the basis for local building codes. Make up air is especially important as buildings get tighter and more efficient. In the next article, we discuss the different types of makeup air units for various applications. Mickey Luongo Mickey is the resident heating and air conditioning expert with over 15 years of experience in the industry.
