Vent-Free Fireplaces: Are They Legal?

Ventless Gas Fireplaces, Indoor Air Quality & Construction Codes

By Brett Dillon

Ventless gas fireplaces have long been a point of contention between builders, homebuyers, appliance manufacturers and building scientists. The appliance manufacturers point out that their products have been approved by various underwriting laboratories for installation in homes. Builders like them because they are a low-cost upgrade that brings a premium profit. Homebuyers like the ambiance of a fireplace but don’t want to spend a lot of money on a vented version. And building scientists criticize them for dangerously compromising indoor air quality.

Builders are unknowingly caught in a quandary—if they install a ventless fireplace in a new home without providing make-up air for that appliance and an exhaust system for removing the combustion by-products, they are in violation of construction codes. In addition to introducing deadly or illness-causing gases like Carbon Monoxide (CO), Carbon Dioxide (CO2) and Nitrogen Dioxide (NO2), unvented gas fireplaces also produce a lot of water or more specifically – water vapor. What dangers are related to this increase in the relative humidity level of the home? Actually, the proliferation of dust mites, mold and mildew, which require at least 50 percent - 70 percent relative humidity to thrive. So an unvented fireplace could terminally poison you and make your house self-compost.

It is much simpler, although slightly more expensive initially, to install a vented or a direct vent gas appliance. By the time the builder has…

• installed a dampered duct to provide combustion air to the vent-free fireplace,
• installed a ducted flue or an exhaust fan that turns on when the fireplace operates,
• removed the combustion gases to the outside of the house, and
• installed a fresh air intake to the mechanical system of the home,

…they could have installed a traditional vented gas fireplace, or better yet, a direct vent gas fireplace.

Furthermore, vent-free fireplaces are not legal in all states, may be in violation of building codes in states where they are legal and create mold concerns, or worse. If you have additional questions about your fireplace system as you attempt to stay warm this winter, don’t hesitate to contact Southface or visit www.southface.org.