Ventless Gas Stoves and Condensation

February 13, 2011 | Filed under: Misc, Roof Repair, Roofing Answers

Beverly recently wrote me the following:

Q: I saw your email address on a net page about metal roof problems. So i’m hoping you can give me a little help. My story, My parents have lived in the same house for 37 years. It has a tin roof with nothing under it . They changed from using a oil heater with a chimney to using a gas stove without a chimney. Their house is sweating now and 1 room is molded like crazy, even the stuff in it. I started putting that mesh looking stuff down seams with tar, but not finished. It is an old house and I don’t want them to end up in an apartment. I think that would kill them. They are old fashioned and always been outside people. So I’m trying to fix this. Did up vents on each side of the house also. It’s just a long house maybe 42 x 28? IDK. I was going to tar the whole thing but I’m still wondering if that’s going to help. Someone told them to put one of those vent things on top.  They also want to go back to using chimney. So do you have any advice for me? I sure hope so. I hate to see them so stressed over this, and they cant fix it (age and health) and can’t afford anyone else. They only get 1200 a month! Thank you for your time. And yes I’m a woman, but I can do anything! I just need a little advice on this one. Thanks

My response:

A: Thanks for your email. I admire you for looking after your folks.

If I had to guess I’d say the problem is entirely due to the ventless gas stove. Those things really pump out the moisture and unless you are venting it away, it will condense.

And in particular if a house is not real well insulated, then the warm moist air will condense on any cool surface including walls and furniture against walls.

I would strongly encourage you to contact the gas stove manufacturer, explain the problem, and get their input.

Venting the attic and insulation your walls and ceilings will help but if there is any way to vent the stove to the outside, I would encourage it highly.

Good attic ventilation by the way requires intake vents, usually in the soffits, and exhaust vents, usually at the ridge.

todd Miller

has spent his entire career in the metal building products manufacturing industry. He is president of Isaiah Industries, an organization recognized as one of the world’s leading metal roofing manufacturers. Todd is currently Vice President of the MRA (Metal Roofing Association) and a Past Chair of MCA (Metal Construction Association). Through his website, he strives to raise the bar on standards and practices to provide property owners with the best possible products for successful roofing projects.

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4 responses to “Ventless Gas Stoves and Condensation”

  1. Al Shatas says:

    I have a 3 Season Room (15×15) and I would like to add a small gas stove ( ie. Vermont Casting) in order to periodically heat the room while in use. The stove will be vented to the outside. The only insulated wall is the one attached to our Condo. The 3 remaining walls and roof are not insulated. Is there a potential for condensation that could cause a problem?

    • Todd Miller says:

      Al, it is very good that the gas stove will be vented. However, as you introduce heat to this room and potentially moisture / humidity from the rest of the house filters into this room, there is indeed increased risk, probably significant, that warm moist air inside the room, will connect with the inside of your cold roof and wall surfaces, and condense there. You might get by with running a dehumidifier in the room. On the other hand, that may not be enough either.

  2. Denise says:

    I also have a ventless gas stove in my 4 season sunroom. One interior wall and uninsulated roof and 3 window walls. I notified last year in the attic mold growing on the new sheething. I just had a new roof and plywood done 2 years ago. I was shocked. Soffets were boarded up with trim in the sunroom as it used to be my outside deck, didn’t want warm air getting into the cold attic. Treated mold with RMR mold killer and dehumidifier ran for a few months to dry everything out up there. Attic fan humidistat set to 60%. Well it’s starting to come back. I leave a window open about 3 inches behind the stove to help vent when it’s running. On and off approx 7 hrs a day when it’s super cold. I live in south jersey. My question is am I better off putting the dehumidifier back in the attic or try it in the sunroom? Or anything I can do, I take care of my dad down the street with Dementia so I don’t have time for this crap! Or should I just throw the stove out and freeze ? I have a heat pump and solar but the gas stove really helps!

    • Todd Miller says:

      Sorry to hear about your dad. I think the dehumidifier in the sunroom would be helpful — better there than the attic in my opinion. I hate to say it but not running the gas stove would also be helpful. Basically, you have warm moist air inside the sunroom migrating to the “attic” and condensing. Adding intake and exhaust vents to the attic will also be helpful. Contact me anytime at

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