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Most cost effective way to bring furnace into house thermal envelope?

jimcava55 | Posted in Energy Efficiency and Durability on

In lieu of Martin’s suggestion; can a propane gas furnace in an attached garage be brought into the house thermal envelope by just framing in around it with insulated walls and access door?
Furnace and hot water tank are vented together.
Preexisting bedroom is on other side of garage wall.
What code violations to avoid?

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  1. wjrobinson | | #1

    Don't even think of doing that. You must get a pro onsite to make drastic changes to carbon monoxide producing objects and enclosing then adhoc and bedrooms.... And ....

    James get onsite pros to help you.

  2. GBA Editor
    Martin Holladay | | #2

    There are several issues you should know about if you want to do this work yourself. The most important issue concerns combustion air. If your furnace and water heater are sealed-combustion units, your work will be simpler. If they are atmospherically vented units, however, they take their combustion air from the room in which they are located.

    If you build partition walls around the furnace, the volume of the room in which it is located is reduced, and you now have to provide ducted combustion air.

    The formulas governing these calculations can be found in most building codes. For example, in the 2006 IRC, the provisions can be found in sections G2407.5 and following.

    If you end up having to provide a combustion-air duct into your new room, you won't be obtaining the energy-efficiency improvements you are looking for.

    One more factor: you'll need to install a layer or two of rigid foam on the floor of the new mechanical room, plus a layer of plywood. This layer must extend under the furnace and water heater.

    This work is important, but it isn't cheap. Most people would arrange to do the work when it's time for a new furnace. When that happens, be sure to choose a sealed-combustion unit.

  3. GBA Editor
    Martin Holladay | | #3

    If you can't afford to bring the furnace inside the conditioned area of your home, you should carefully seal all duct seams with mastic. (The real problem is the seams in the furnace itself; some of these seams are around access doors and shouldn't be sealed with mastic. HVAC tape is the best solution to these seams.)

    Then insulate all exposed ductwork, if it isn't already insulated.

  4. user-723121 | | #4

    I added a mechanical room to the front of an attached garage for a master suite that was built over the garage. It worked very well and I had no issues with plan review or the building inspector. The mechanical room contained a gas water heater and forced air furnace.

    Check the applicable codes in your area before starting the project.

  5. jimcava55 | | #5

    Thanks to all!
    The furnace and water heater are only three years old and they are staying where they are.
    Seams on furnace are HVAC taped and exhaust seams are sealed.
    Where exhaust penetrates through attic floor is also sealed with fire block caulk and foam.

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