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My home has a direct-vent gas fire place on the ground floor, and each winter the area around the fire place inside the house becomes very cold (granite finish). On colder days, the carpeted floor area near the fireplace is also cold. The fire place is rarely used, but is insulated above and under its enclosure (I can't tell if the sides are insulated, but the adjacent drywall is).

I have researched this "cold air" problem and many other forum posts describe the issue as a draft, but none give solutions other than "call the contractor who installed it", or "that shouldn't happen". To be clear, the problem is not a draft but rather heat loss via radiation and conduction; I can not detect a draft or airflow in the immediate area around the fire place.

Is this type of fire place inherently vulnerable to cold infiltration by its design? It seems that since the venting pipe is always open and allowing outside air into the combustion chamber, then there is a always going to be some heat loss, especially when there is a large temperature difference between inside and outside the house.

If this isn't supposed to happen, then what can I do to rectify the problem? I have already filled the control area below the fire place with towels and blankets (when not in use), but that isn't making a significant impact.

EDIT:

After further investigation, there is a draft originating from somewhere behind the fireplace installation. In the control area (below the combustion chamber), air comes into my room from anywhere where there is a hole in the sheet metal. I will have to start looking for cracks under the fireplace via the crawlspace, and outside of the home in the area that encloses the vent pipe.

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See also: diy.stackexchange.com/questions/271/… –  Steve Guidi Jan 15 '13 at 18:06
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2 Answers 2

It is very important to ensure all infiltration paths a sealed off and adjacent walls and floor are properly insulated. Even a hairline crack in the doors can cause enough infiltration to lower temperatures in the area, though no actual moving air can be detected.

Even so, the fact that outside air can freely circulate in the combustion chamber will also be a heat sink, lowering temperatures in the area. More sophisticated devices similar to this utilize automatic dampers that interlock with the fuel supply. These are located on the exhaust flue, and sometimes on the combustion air inlet as well. I don't know if retrofitting such devices is possible on typical residential fireplaces. Such a project must be done very carefully to ensure complete safety. Failure of the system can result in carbon monoxide poisoning, so multiple fail safe measures are called for. Such measures are beyond the abilities of nearly all DIY practitioners. Only fully qualified professionals should perform this sort of work.

Even more so, though flue dampers prevent cold air from freely circulating, they are typically thin sheets of metal with poorly sealed edges, so the fire box will still be fairly cold, albeit much less so.

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When we bought our house new, I tried poking around everything I could. Did this with the fireplace (direct-vent, gas), too.

Unfortunately, I didn't figure out how to set the glass cover back correctly, and we had to endure a couple weeks of sub-zero temperatures to 5ft around the fireplace, until the builder showed me what had gone wrong.

Could be worth a try..

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