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Community and Q&A

Attic insulation

Jeff Cannon | Posted in General Questions on

I’m curious if anyone has any advice with concern to insulating an attic that contains a gas furnace (sealed combustion)? The unit is placed pretty close to the rafters- about 8″- and the attic is only about 5′ at the ridge. Is it best to create a conditioned space for the unit or the whole attic? I’m new to all of this, so I’m not sure what to watch out for. Any advice would be appreciated. Also, does anyone have any recommendations for insulation contractors in the Boston area?

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  1. GBA Editor
    Martin Holladay | | #1

    It's usually better to convert the entire attic to an unvented conditioned attic rather than to try to build a small mechanical room around the furnace, especially if there are already concerns (as in your case) that the furnace is rather close to the ridge. The main reason for this advice to to make sure that the ducts as well as the furnace end up within the conditioned space.

    That said, a tight attic is never a good place for a furnace, and your attic may be undesirable for several reasons, including access for maintenance. In some homes, it may make more sense to use a few ductless minisplit units to condition the top floor rather than to use a furnace located in a tight attic.

    If you decide to go ahead and convert the attic to an unvented conditioned attic, it's important to take fire safety seriously. Since spray foam insulation is flammable, the best installations include drywall on the interior side of any spray foam that might be installed.

    For more information on these issues, see this article: Creating a Conditioned Attic.

  2. Jeff Cannon | | #2

    Thanks, Martin!

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