ADUs and garage conversions are everywhere in the San Fernando Valley, and one of the first questions is how to keep them comfortable. A space that bakes in summer and gets chilly on winter nights needs its own plan for heating and cooling.
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Why the main house system often isn’t the answer
- Size: most home systems were sized for the main house. Adding a new space can leave both too warm or too cold.
- Distance: a detached ADU or a garage at the far end of the house is a long, costly duct run.
- Separate living: if someone lives in the ADU, they usually want their own thermostat.
Common options
Ductless mini-split heat pump
The most common choice for ADUs and garage conversions. An outdoor unit connects to one or more indoor heads through a small hole in the wall, with no ductwork. It heats and cools, each room can have its own control, and modern units are efficient in Valley heat. See ductless mini-splits.
A small ducted heat pump or furnace
For a larger ADU with several rooms, a small ducted system can make sense, especially in new construction where ducts are easy to run before the walls close.
Extending the main system
For an attached conversion close to the existing ducts, extending the system can work if it has enough capacity. A contractor should check before you assume it does.
Wall heaters and window units
Cheaper up front, but they rarely meet comfort or efficiency expectations for a space someone lives in, and they may not satisfy the permit for a legal ADU.
Things to plan for
- Insulation first: a garage often has thin walls, an uninsulated ceiling and a big door opening. Insulating well makes a smaller, cheaper system work.
- Electrical capacity: a heat pump needs its own circuit. Older panels may need an upgrade, which is a job for a licensed electrician.
- Permits and energy rules: new ADUs go through plan check, and the HVAC work is usually part of it. Your builder or HVAC contractor should handle the HVAC permit.
- Outdoor unit placement: think about noise near bedrooms and neighbors, and keep it clear of dry brush in fire-prone areas.
Questions to ask an HVAC contractor
- Did you do a load calculation for this space, or are you guessing the size?
- Ductless, ducted, or extend the main system, and why?
- Does the price include the permit, electrical connection and condensate drain?
- Are you licensed with the CSLB (C-20) and insured? You can check at CSLB.ca.gov.
Comparing quotes? See heat pump vs. furnace in the Valley and heating installation.
Need a licensed pro?
Building or converting? We’ll connect you with an independent, licensed local HVAC contractor who does ADU and conversion work. It’s free for homeowners.
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