A Zero Clearance Fireplace typically refers to a fireplace that was designed so that it can sit right next to the framing. To do this the fireplace must contain and control the heat so that the surface temperature of the fireplace exterior sitting next to the framing remains cool and does not create any chance of a fire hazard.

The quality and efficiency of different zero clearance fireplaces varies widely.  EPA Certified fireplaces are going to be the most efficient and include features such as outside air sources sufficient to satisfy all combustion air needs, controllers for the combustion air intake that allow the heat ouput and burn time to be controlled by the home owner and glass doors that are gasketed or sealed.

The lesser zero clearance fireplaces will have either none or only some of these features.  The very poorest will actually pull more air out of the house than they give back in heat so the net effect will be to make it colder rather than warmer.

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