GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

To build garage mechanical room under living space inside?

user-956864 | Posted in Energy Efficiency and Durability on

The plans show a mechanical room in the basement garage under living space in zone 4. The HVAC is direct vented and the water heater is electric. I guess considering that combustion in living space is not a concern, does the furnace and water heater work better in the conditioned space than the garage under living space but considered outside ( colder in winter, hotter in summer?)

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. GBA Editor
    Martin Holladay | | #1

    It is always best to locate all HVAC equipment inside a home's conditioned space. A garage should never be included within a home's conditioned space.

    Ideally, your HVAC equipment and water heater will be relocated to a mechanical room inside your house.

    Any house with a basement garage needs a careful air-sealing plan (verified by blower-door testing and possibly the use of a theatrical fog machine) to be sure that there is a very tight air barrier between the garage and the living space.

  2. user-956864 | | #2

    Thanks Martin, to be clear I am attaching the plan and asking if I can uninsulate between the basement and the mechanical room though there is no door to the inside there. I would then insulate between the mechanical room and ambient ground to R-10 on one side and the garage space to R-13 on the other two sides. Now the mechanical room would be sealed from the garage in the garage basement but inside the living space temperature wise. The ductwork and equipment would be inside. I feel like I have answered my own question by asking it to you. Thanks for thinking out loud with me.

  3. GBA Editor
    Martin Holladay | | #3

    In theory, your idea might work. But be careful:

    1. The slab is a big thermal bridge, so you'll have to build a raised, insulated, framed floor for your mechanical room.

    2. You need an exterior door on the mechanical room with very good weatherstripping.

    3. The walls of your mechanical room need to be air sealed and insulated to the same level as your above-grade exterior walls.

    4. Your mechanical room may need combustion makeup air if any equipment is not sealed-combustion.

  4. user-651098 | | #4

    For good info on attached garages and indoor air quality, connect to the website. At the top right of the home page, enter "attached garage" in the search box. That will lead you to several excellent documents. - Jim

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |