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Direct vent gas through wall vs roof in home with spray foam insulation

Dburger | Posted in General Questions on

I have a 1 ½ story house in climate zone 5A that has spray foam insulation in the walls and roof. I’m planning to install a direct vent gas stove in an outside corner of the family room. The vent will penetrate the ceiling and enter the attic space behind the knee wall of the upstairs. This attic space is considered conditioned space and is completely air sealed to the outside. At this point, would it be better to vent through the wall or through the roof? I know a 1” clearance to combustibles must be maintained around the vent pipe either way. I hate the thought of putting a hole through the building envelope but I’m particularly concerned about putting an uninsulated hole through the roof when the rest of the roof is foamed. Could this lead to moisture problems in this area of the roof or potentially lead to ice dams in the winter? Seems like it would be less of an impact to the envelope going through the wall. The downside of going through the wall would be an ugly vent cap on the front of my house. Any recommendations?

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Darren,
    First of all, what do you mean by a "direct vent gas stove"? Is it a gas-fired space heater? Or a kitchen range with a range hood?

    Assuming it is a gas-fired space heater, the first step is to verify that the appliance manufacturer allows both types of venting (through-the-roof venting and sidewall venting).

    The risk of contributing to ice dams is real. Whether this is a concern depends on whether you live in a snowy part of Climate Zone 5 or a not-so-snowy part of Climate Zone 5.

    If you get lots of snow, that factor tips the balance in favor of through-the-wall venting (assuming that type of venting is allowed by the appliance manufacturer).

  2. Dburger | | #2

    It is a space heater, Lopi Greenfield. Looks like a woodburner only with gas logs. the manual allows venting through the roof or the wall. We generally do not get a lot of snow but that varies year to year. We've certainly had rough winters where snow piles up on the roof for long periods of time. Are there any considerations specific to the foam insulation? Also, how would you air seal around the vent pipe?

  3. GBA Editor
    Martin Holladay | | #3

    Darren,
    Q. "Are there any considerations specific to the foam insulation? Also, how would you air seal around the vent pipe?"

    A. Venting systems are proprietary systems, and they vary. It is essential that you follow the installation instructions provided by the appliance manufacturer and the manufacturer of the metal chimney that you choose to install. If you have specific questions about clearances, direct the questions to the manufacturer of the metal chimney or venting system.

    For general advice about air sealing around chimneys, see Air Sealing an Attic.

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