Make Up Air Units: A Guide to Different Models for Different Needs Posted on August 24, 2022 In the previous article, we explained the concept of makeup air and its necessity for most indoor buildings. In this installment, we delve into what a makeup air unit is and explore the different types of makeup air systems tailored for various applications. Contents ToggleWhat is Makeup Air?What are Makeup Air Units?Components of a Makeup Air UnitWhat are Makeup Air Modules?Types of Makeup Air ModulesMakeup Air FanDirect Gas Fired HeatIndirect Gas Fired HeatNon-Gas Fired Makeup Air UnitsDX CoolingChilled Water CoolingEvaporative CoolingWhere are Makeup Air Systems Required?Residential HomesMinimum Ventilation RequirementsOur Recommended Makeup Air UnitsFor Residential Makeup Air What is Makeup Air? Makeup air is controlled outside air that replaces the air exhausted from inside the building. As indoor air is expelled, it creates negative pressure, causing outside air to rush in to fill the void. What are Makeup Air Units? Makeup air units are devices designed to compensate for pressure differences and ensure an adequate supply of filtered air for safety and comfort. Without makeup air systems, sealed structures can experience issues caused by negative interior air pressure, including: Contaminants and allergens Persistent odors Humidity problems Inefficient HVAC operation Higher utility costs Components of a Makeup Air Unit A makeup air unit shares many components with fans, air handlers, or air conditioners. The major parts include: Key Components of a Makeup Air Unit Intake: The opening where outside air enters and feeds into the unit. Back-draft Damper: Controls airflow to move only in one direction, preventing reverse airflow. Essential for maintaining air quality and system integrity. Filters: Trap contaminants like pollutants, toxins, and allergens, ensuring clean air enters the building. Heating/Cooling Elements: Modify the temperature of incoming air for occupant comfort and reduced HVAC load. Ducts and Registers: Transport processed air throughout the interior spaces. Exhaust Fan: Expels used air out of the building, maintaining air balance. Optional features and advanced functions may include: Recirculation features Variable volume control Building pressure controls High-temperature discharge Multi-stage or ultraviolet light filtration What are Makeup Air Modules? Some makeup air units are modular, allowing for additional heating or cooling sections. This design is particularly suited for larger or industrial models, providing flexibility to meet varying needs and operational requirements. Types of Makeup Air Modules Makeup air modules vary primarily based on air treatment or cooling methods. The main types include: Varieties of Makeup Air Modules Makeup Air Fan Also known as an untempered makeup air unit or fan box, this is the simplest type of MUA. It consists of an intake fan that brings in air without any heating or cooling equipment, ideal for consistent temperate climates or where specific indoor conditions are not critical. Direct Gas Fired Heat A direct-fired makeup air heater uses natural gas or propane to heat incoming air before circulating it into the building. This method is highly efficient, delivering 100% of generated heat into the interior. However, it introduces gas byproducts, which must be managed with proper filters and safety equipment. ANSI standards mandate that up to 85% of the air can be recirculated. Direct gas-fired MUAs can be further classified into: Compact low CFM Direct Fire Heater Modular Direct Fired Heater Horizontal Industrial Direct Fired Heater Vertical Industrial Direct Fired Heater Indirect Gas Fired Heat These units use an indirect heating method similar to home furnaces, where a heat exchanger contains the gas flame, ensuring no gas byproducts mix with the air. Although less efficient than direct-fired MUAs, they provide cleaner air suitable for spaces sensitive to mold. Non-Gas Fired Makeup Air Units These MUAs are powered by steam, hot water, or electricity, each with its own advantages and limitations compared to gas-fired systems. DX Cooling Direct Expansion (DX) cooling uses refrigerant coils to cool the air supply. The refrigerant absorbs heat as air passes through the coils, and the system can be configured with built-in or modular condensers. Chilled Water Cooling Chiller units use cold water to cool the air, suitable for large air handling units servicing extensive indoor spaces. Evaporative Cooling Evaporative coolers add humidity to the air, ideal for hot and dry climates to maintain interior humidity while cooling. Where are Makeup Air Systems Required? Residential Homes Impact of Makeup Air in Sealed Homes Tightly sealed houses can result in unequal pressure, even when doors are opened. Powerful range hoods and other appliances can cause negative air pressure, leading to unfiltered air seeping in through gaps, holes, or cracks. The most common exhaust appliances include: Bathroom exhaust fans (40‐200 CFM) Clothes dryers (100‐225 CFM) Kitchen range hoods (100‐1,500 CFM) According to the International Residential Code Section M1503.4 and the International Mechanical Code Section 505.2, makeup air units are required for all domestic range hoods exceeding 400 CFM, equipped with at least one damper. “Exhaust hood systems capable of exhausting in excess of 400 cfm (0.19 m3/s) shall be provided with makeup air at a rate approximately equal to the exhaust air rate. Such makeup air systems shall be equipped with a means of closure and shall be automatically controlled to start and operate simultaneously with the exhaust system.” Minimum Ventilation Requirements Space Occupant Density (per 1,000 sq. ft) CFM per Person CFM per Sq Ft. Exhaust Airflow Rate (CFM / sq ft) Living areas 1st bedroom: 2 Succeeding bedrooms: 1 per room 0.35 ACH, and at least 15 CFM / person N/A N/A Bathroom N/A N/A N/A 20/50 The ASHRAE Standard 62.2 also mandates adequate makeup air for residential buildings, with most states having their own specific codes. Our Recommended Makeup Air Units For Residential Makeup Air The International Residential Code requires makeup air for all kitchen hoods capable of exhausting 400 or more CFM. These makeup air units are suitable for most home range hoods and household appliances, some featuring inverter technology for enhanced efficiency. Note: Makeup air PTAC units are not recommended for use within two miles of coastal areas. GE AZ65H07DBM 7000 BTU Zoneline PTAC with Heat Pump This PTAC unit combines cooling and makeup air functions, delivering 25 – 50 CFMs of continuous makeup air with up to 7,000 BTU of cooling power. It also dehumidifies incoming air when relative humidity exceeds 55% and outdoor temperatures are above 50°F. GE’s Zoneline units are among the quietest PTACs available, boasting a sound transmission class of 29. Price: $1,729.00 GE AZ65H07DBM 7000 BTU Zoneline PTAC with Heat Pump - Makeup Air - Power Cord Included For your convenience, we are including a required power cord of your choice with this unit. Choose either a standard power cord (included) or a hardwi... View Product Mickey Luongo Mickey is the resident heating and air conditioning expert with over 15 years of experience in the industry.
In the previous article, we explained the concept of makeup air and its necessity for most indoor buildings. In this installment, we delve into what a makeup air unit is and explore the different types of makeup air systems tailored for various applications. Contents ToggleWhat is Makeup Air?What are Makeup Air Units?Components of a Makeup Air UnitWhat are Makeup Air Modules?Types of Makeup Air ModulesMakeup Air FanDirect Gas Fired HeatIndirect Gas Fired HeatNon-Gas Fired Makeup Air UnitsDX CoolingChilled Water CoolingEvaporative CoolingWhere are Makeup Air Systems Required?Residential HomesMinimum Ventilation RequirementsOur Recommended Makeup Air UnitsFor Residential Makeup Air What is Makeup Air? Makeup air is controlled outside air that replaces the air exhausted from inside the building. As indoor air is expelled, it creates negative pressure, causing outside air to rush in to fill the void. What are Makeup Air Units? Makeup air units are devices designed to compensate for pressure differences and ensure an adequate supply of filtered air for safety and comfort. Without makeup air systems, sealed structures can experience issues caused by negative interior air pressure, including: Contaminants and allergens Persistent odors Humidity problems Inefficient HVAC operation Higher utility costs Components of a Makeup Air Unit A makeup air unit shares many components with fans, air handlers, or air conditioners. The major parts include: Key Components of a Makeup Air Unit Intake: The opening where outside air enters and feeds into the unit. Back-draft Damper: Controls airflow to move only in one direction, preventing reverse airflow. Essential for maintaining air quality and system integrity. Filters: Trap contaminants like pollutants, toxins, and allergens, ensuring clean air enters the building. Heating/Cooling Elements: Modify the temperature of incoming air for occupant comfort and reduced HVAC load. Ducts and Registers: Transport processed air throughout the interior spaces. Exhaust Fan: Expels used air out of the building, maintaining air balance. Optional features and advanced functions may include: Recirculation features Variable volume control Building pressure controls High-temperature discharge Multi-stage or ultraviolet light filtration What are Makeup Air Modules? Some makeup air units are modular, allowing for additional heating or cooling sections. This design is particularly suited for larger or industrial models, providing flexibility to meet varying needs and operational requirements. Types of Makeup Air Modules Makeup air modules vary primarily based on air treatment or cooling methods. The main types include: Varieties of Makeup Air Modules Makeup Air Fan Also known as an untempered makeup air unit or fan box, this is the simplest type of MUA. It consists of an intake fan that brings in air without any heating or cooling equipment, ideal for consistent temperate climates or where specific indoor conditions are not critical. Direct Gas Fired Heat A direct-fired makeup air heater uses natural gas or propane to heat incoming air before circulating it into the building. This method is highly efficient, delivering 100% of generated heat into the interior. However, it introduces gas byproducts, which must be managed with proper filters and safety equipment. ANSI standards mandate that up to 85% of the air can be recirculated. Direct gas-fired MUAs can be further classified into: Compact low CFM Direct Fire Heater Modular Direct Fired Heater Horizontal Industrial Direct Fired Heater Vertical Industrial Direct Fired Heater Indirect Gas Fired Heat These units use an indirect heating method similar to home furnaces, where a heat exchanger contains the gas flame, ensuring no gas byproducts mix with the air. Although less efficient than direct-fired MUAs, they provide cleaner air suitable for spaces sensitive to mold. Non-Gas Fired Makeup Air Units These MUAs are powered by steam, hot water, or electricity, each with its own advantages and limitations compared to gas-fired systems. DX Cooling Direct Expansion (DX) cooling uses refrigerant coils to cool the air supply. The refrigerant absorbs heat as air passes through the coils, and the system can be configured with built-in or modular condensers. Chilled Water Cooling Chiller units use cold water to cool the air, suitable for large air handling units servicing extensive indoor spaces. Evaporative Cooling Evaporative coolers add humidity to the air, ideal for hot and dry climates to maintain interior humidity while cooling. Where are Makeup Air Systems Required? Residential Homes Impact of Makeup Air in Sealed Homes Tightly sealed houses can result in unequal pressure, even when doors are opened. Powerful range hoods and other appliances can cause negative air pressure, leading to unfiltered air seeping in through gaps, holes, or cracks. The most common exhaust appliances include: Bathroom exhaust fans (40‐200 CFM) Clothes dryers (100‐225 CFM) Kitchen range hoods (100‐1,500 CFM) According to the International Residential Code Section M1503.4 and the International Mechanical Code Section 505.2, makeup air units are required for all domestic range hoods exceeding 400 CFM, equipped with at least one damper. “Exhaust hood systems capable of exhausting in excess of 400 cfm (0.19 m3/s) shall be provided with makeup air at a rate approximately equal to the exhaust air rate. Such makeup air systems shall be equipped with a means of closure and shall be automatically controlled to start and operate simultaneously with the exhaust system.” Minimum Ventilation Requirements Space Occupant Density (per 1,000 sq. ft) CFM per Person CFM per Sq Ft. Exhaust Airflow Rate (CFM / sq ft) Living areas 1st bedroom: 2 Succeeding bedrooms: 1 per room 0.35 ACH, and at least 15 CFM / person N/A N/A Bathroom N/A N/A N/A 20/50 The ASHRAE Standard 62.2 also mandates adequate makeup air for residential buildings, with most states having their own specific codes. Our Recommended Makeup Air Units For Residential Makeup Air The International Residential Code requires makeup air for all kitchen hoods capable of exhausting 400 or more CFM. These makeup air units are suitable for most home range hoods and household appliances, some featuring inverter technology for enhanced efficiency. Note: Makeup air PTAC units are not recommended for use within two miles of coastal areas. GE AZ65H07DBM 7000 BTU Zoneline PTAC with Heat Pump This PTAC unit combines cooling and makeup air functions, delivering 25 – 50 CFMs of continuous makeup air with up to 7,000 BTU of cooling power. It also dehumidifies incoming air when relative humidity exceeds 55% and outdoor temperatures are above 50°F. GE’s Zoneline units are among the quietest PTACs available, boasting a sound transmission class of 29. Price: $1,729.00 GE AZ65H07DBM 7000 BTU Zoneline PTAC with Heat Pump - Makeup Air - Power Cord Included For your convenience, we are including a required power cord of your choice with this unit. Choose either a standard power cord (included) or a hardwi... View Product
