Rooftop vs Ground-Mounted Make-Up Air Units
Every paint booth, blast room and prep station exhausts air, and a make-up air unit replaces it with filtered, often heated, outside air. Where that unit sits affects the building, the ductwork, how easily it can be maintained, and how long it lasts. Rooftop units sit on a curb or rails on the roof. Ground-mounted units sit on a pad outside or on a platform or floor inside the building. Each placement suits different buildings and operations.
Discuss your installationRoof Structure and Loads
A rooftop unit adds significant weight to the roof structure. The roof must be checked for capacity, and the unit usually needs a curb or steel rails that transfer loads to the building frame. Older buildings, light metal roofs and buildings with existing rooftop equipment may need structural reinforcement or engineering review. Roof penetrations for supply ducts, gas lines and electrical must be flashed and sealed properly to prevent leaks. Ground-mounted units avoid roof loading entirely, needing only a properly built concrete pad or floor support, though they require a path for ductwork into the building. Also consider how the unit will be replaced someday. A rooftop unit set by crane during construction may be much harder to remove once neighboring buildings, power lines or new equipment surround the site.
- Obtain building drawings or roof framing information before planning rooftop units.
- Consider the age and condition of the roof membrane.
- Plan crane access for setting rooftop equipment.
Getting Technicians to the Equipment
Make-up air units need regular service: filter changes, belt and bearing checks, burner inspection and controls testing. On the roof, technicians need safe access, which means a roof hatch or ladder, fall protection near edges, and good weather. Hauling filters and parts up adds time. Ground-mounted units are easier to reach, so routine maintenance tends to happen more consistently. If the unit is inside the building, it can be serviced in any weather. Poor access is one of the most common reasons booth make-up air units go unmaintained.
Duct Routing and Airflow Paths
A rooftop unit often sits directly above or near the booth, allowing a short, straight supply duct down into the booth plenum. That keeps duct costs and pressure losses low. A ground-mounted unit beside the building needs ductwork that runs up the wall and across to the booth intake, which can be longer and include more fittings. Inside the building, ground units may need ducts routed above other equipment. Longer duct runs require attention to sizing, insulation and support. The exhaust stack location also matters: supply intake and exhaust discharge must be separated so contaminated exhaust is not drawn back into the make-up air. Gas piping and electrical feeds follow the unit as well. A rooftop unit needs gas run up and across the roof on proper supports, while a ground unit may sit closer to the meter and main electrical gear, shortening those runs.
- Map the shortest practical supply route to the booth.
- Keep the intake well away from exhaust stacks and truck docks.
Weather, Noise and Equipment Life
Rooftop units are fully exposed to sun, rain, wind, hail and temperature extremes. Cabinets, controls and components must be rated for outdoor use, and corrosion, especially near coastal or industrial environments, shortens equipment life without maintenance. Ground-mounted outdoor units face similar exposure but are easier to protect and inspect. Indoor ground units avoid weather but take up floor space and add noise to the work area. Noise from rooftop units may matter if the building is near residential properties. Filters on outdoor units load faster in dusty yards, near gravel lots or during pollen season, so intake hoods and filter sections should be easy to open and inspect no matter where the unit sits.
Space and Site Constraints
Ground-mounted units need floor or yard space. Outside, the pad must be accessible for service and protected from vehicles, and the area must allow clearances around the unit. Inside, the unit consumes floor space that might otherwise be used for production. Rooftop units save floor space but need roof area and structural capacity. For leased buildings, landlords may restrict roof penetrations or require restoration at the end of the lease. Look at the full site, including truck traffic, setbacks and future expansion, before choosing. When information is gathered, an installer can compare both options with real numbers for your building. Future booths or ovens may need their own units, so leave space on the roof or in the yard.
Frequently asked questions
Is a rooftop make-up air unit always cheaper to install?
Not always. It saves floor space and often duct length, but may require structural work, crane setting and roof penetrations.
Can a make-up air unit be installed inside the building?
Yes. Indoor units are serviced easily in any weather, but need floor space, an outside air intake and ductwork.
How far should the intake be from the booth exhaust?
Far enough to avoid drawing exhaust back into the supply air. The required separation depends on the layout and local requirements.
Does a rooftop unit need roof reinforcement?
It depends on the roof's structure and the unit's weight. An engineering review is often recommended, especially on older or lightweight roofs.
Which option is easier to maintain?
Ground-mounted units are generally easier to reach and service, which often leads to better maintenance.
What information helps choose placement?
Roof structure and condition, available yard or floor space, duct routes, utility locations, lease terms and service access.