Featuring America's Home Inspector: Nationally Syndicated Columnist, Barry Stone

The House Detective:  by Barry Stone, Certified Home Inspector

Dear Barry: A few weeks ago, my landlord installed an old, unvented gas heater in my apartment. Whenever I use it, the place becomes as humid as a steam room, and mold has appeared on some of the walls. I’ve complained, but my landlord says the mold is caused by my dogs. Does that seem plausible, or is the mold caused by the heater?  Elizabeth

Dear Elizabeth: Mold is caused by excessive moisture. The exhaust from a gas-burning fixture is mainly carbon dioxide and steam. Most gas heaters are vented to the outside, but an unvented heater expels exhaust, including steam, inside the building. If the mold began after the heater was installed, then the cause is obviously moisture condensation from the steam that is emitted by the heater.

As for your landlord’s canine excuse, that’s a dogged ploy if I ever heard one. Who ever heard of mold being caused by dogs? The unvented heater is a health and safety hazard and should not be used. Furthermore, if combustion problems ever occur with that kind of heater, you could have carbon monoxide instead of carbon dioxide, and that could be deadly. Your landlord should address this matter immediately. First, the gas heater should be replaced with a vented heater, and the replacement should be done by a license heating contractor. Then, the mold should be mitigated by a qualified expert.