By Jody Waverek, PE

Generally speaking, outdoor mechanical HVAC equipment, such as air-source heat pumps, are located outdoors for a reason: to extract or reject heat from the outdoor air.

With most construction projects, installing HVAC equipment outside of the building does not present a problem because the equipment either may not require a large amount of space or can be hidden on the backside of the building out of the view of the public or occupants.

However, in some cases, installing your mechanical equipment outside may not be feasible. Some reasons may include the following:

  • Physical constraints where the project site has limited or no exterior real estate for conventional outdoor mechanical equipment.
  • Architectural aesthetics where the owner and/or design team has determined that outdoor equipment must not be visible from any view.
  • Extreme climate conditions exceed the low-end performance range for air-source heat pump operation.
  • Radiated noise constraints are set forth by the owner, jurisdiction, or neighbors.
  • Architectural elements such as sloping roofs, overhangs, or enclosures that prevent the recommended installation or operation of mechanical equipment.

If any of these situations apply to your project—and all other solutions, including rooftop designs, have been exhausted—you may want to consider placing the necessary air source heat pump units in a conditioned enclosure or “doghouse.”

How Do “Doghouses” Work?

To provide the best possible outcome, it’s helpful to understand how doghouses work.

In most instances, doghouses are only considered when outdoor air-source mechanical equipment, for reasons listed above, can’t be located outdoors. Such is the case when the mechanical system selected is an air-source heat pump in a region with a cold climate. Air-source heat pumps have limited ambient conditions where they can operate and still produce useful heat. Most modern heat pump equipment can operate effectively in conditions as low as -15°F. In extreme climates, winter temperatures can drop well below the equipment’s lower operating limits, rendering the unit non-functional.