The term "HVAC" refers to heating, ventilation and air conditioning systems. All appliances, ducts, wiring, vents, pipes and other components of heating, cooling or ventilating elements comprise parts of the HVAC system. HVAC systems can be mounted on the roof, though various factors affect how this is done, including the type of HVAC units involved, type of roof on your home, and the relationship between your roof and the HVAC unit.
Some HVAC units exist specifically for rooftop installation. These units consist of large, box-like structures containing a furnace unit for heating and an air conditioning unit for cooling. Rooftop HVAC units also contain numerous inlet and exhaust areas for transporting heated and cooled air into the home from above, and for ventilating the unit properly. These appliances contain numerous electrical components and require connection to electrical wiring from below, through the roof. A metal casing around the unit protects the electrical system from weather damage.
Mounting Rooftop HVAC
Manufacturers design rooftop HVAC units for flat roofs. An HVAC professional or team can install such a unit easily on your flat roof. However, if your roof exhibits pitch, or slope, installation becomes difficult. First, you need a flat area for the unit. A platform can be built on a sloped roof to accommodate a flat HVAC unit if your roof contains no flat spots. However, even if you build a platform, keep in mind that HVAC professionals are not trained to work on sloped roofs and may not take the job due to the danger involved in placing a very heavy piece of equipment on a sloped space.
Various factors affect whether you can mount an HVAC unit on your roof, notably the strength of your roof and weight of the unit. All roofs, pitched or flat, come with a maximum load bearing capacity, or the total amount of weight a roof can support before it collapses. This usually is measured in pounds per square foot (PSF). Always determine whether your roof can support the weight of an HVAC system before installation. HVAC professionals also must inspect your attic and roof area to ensure than all vents, ducts and electrical wiring that connect to the unit can fit in your space while meeting local building code laws.
Other HVAC Units
Ostensibly, you can mount any HVAC unit you want on a roof. However, mounting a non-rooftop HVAC unit on a roof may present a number of problems. Never mount any unit designed for indoor use on a roof because they possess no protection against weather. Units designed for outdoor use on the ground, meanwhile, contain an improper inlet and exhaust setup for roof use. A roof unit needs electricity and venting from below, while ground units contain these on the sides or top. Always contact an HVAC professional before mounting a unit on roof, for consultation if nothing else.
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