Photo of an evaporative cooler or swamp cooler in Tucson (C) Daniel Friedman Rooftop HVAC Air Conditioning & Heat Systems

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Rooftop HVAC equipment: this article describes rooftop mounted HVAC systems - rooftop air conditioners, rooftop heat pumps, and rooftop heating equipment. We describe types of roof-mounted HVAC equipment and common inspection points, operating problems, and repair approaches. At page top is a roof mounted swamp cooler or evaporative cooling system on a private home in Tucson.

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Roof-mounted Air Conditioners, Heat Pumps, Heating Systems

Commercial rooftop-mounted combined air conditioning or heat pump units

Photograph of commercial rooftop mounted A/C system Photograph of commercial rooftop mounted A/C system

Rooftop mounted central air conditioning systems may include both the cooling unit (evaporator coil, blower fan, filters) and the compressor/condenser unit in one package. At above right is a complex of roof-mounted AC/heat pump systems on a Christchurch, New Zealand high rise building roof. These units may be a bit crowded as well as blown-on by the building's ventilation system openings at the upper right of the image.

At above left is a flat-roof mounted commercial cooling system located in New York.

Rooftop mounted central cooling systems may be smaller packaged systems which blow their cool air down directly into the cooled space through an opening in the roof, drawing return air from a nearby location, or the rooftop cooling system may be connected to duct work which in turn blows down into multiple building areas to deliver cool air, drawing return air from one or more centralized returns.

In many commercial installations, the entire area over a suspended ceiling may serve as one giant return plenum through which pass the supply ducts, delivering air to individual supply registers.

While the list above describes the common components of a typical residential air conditioning system, other configurations and packaged units are also in increased use in both residential and commercial installations.

Alternative HVAC designs may combine all components except for the duct work in a rooftop mounted unit such as the one shown above where it was mounted on a flat roof over offices at a commercial building.

Split-System A/C Rooftop Mounted Air Conditioners & Heat Pumps

A/C service switch outdoors (C) Daniel Friedman

The outdoor compressor/condenser unit of split-system air conditioners and heat pumps is also commonly mounted on rooftops, especially flat or low-slope roofs such as the unit shown at left.

Installation requirements for rooftop-mounted split system compressors / condenser units include both a service disconnect (circled in our photo) and often additional measures to assure that the unit is properly padded to avoid damage to the roof membrane, and to assure that the unit is properly levelled.

IN our OPINION, where rooftop mounted split system condenser units are exposed to high temperatures system operating efficiency and costs may be affeted.


Rooftop HVAC Duct System Leaks & Water, Mold, and Pathogens

Photograph of rooftop ducts leak water into fg lined duct Photograph of interior of leaked-into fg lined rooftop duct

These photographs show what happens when a rooftop packaged-terminal air-conditioning air handler
(PTAC) and horizontal runs of air-ducts are installed on a roof surface and when that air duct system is improperly sealed and also is lined with fiberglass insulation.

Water ponded on the old, concave sections of air conditioning ducts on the roof of this commercial office space. As water leaked into the duct system it saturated fiberglass duct liner which in turn, had its normal coating of organic dust and debris from the building, risking an indoor mold or pathogen problem for some of the occupants.

The cure for these duct leaks was costly: it was determined that it was less costly to completely replace the rooftop ducts with new metal ducts using outside insulation than it would have been to remove the contaminated fiberglass liner, clean the existing ducts, repair the leaks, and insulate their exterior. The work was combined with other building HVAC cleaning and repairs.

Support Requirements for Rooftop-Mounted HVAC Equipment

Rooftop air conditioning units, Christchurch New Zealand (C) Daniel FriedmanCommon inspection points & functional issues around rootop-mounted HVAC equipment include:

  • adequacy of structural support - weight distribution
  • proper mounting and flashing at support base to avoid roof leaks
  • provision for working space for maintenance and repair
  • leaks into the HVAC equipment or duct system (described above)


Shown at left, support system for rooftop air conditioners / heat pumps mounted on a metal roof in Christchurch, New Zealand.




Continue reading at SPLIT SYSTEM Ductless Air Conditioners or select a topic from the More Reading links shown below.


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ROOFTOP A/C / HEAT PUMP at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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