gas heater vs. fireplace insert
We’re preparing to replace our woodstove, which has fed into a fireplace through a liner, with some form of gas heater. Our county’s air quality folks are imposing no-burn days in the winter, always on the days we need the heat the most; and this has been part of our household heating.
This will be part of a remodel of the room in question, and we’re contemplating either a gas fireplace insert, feeding, probably through a liner, up the existing tile-and-concrete chimney; or removing the chimney, framing an insulated wall around the space, and putting in a gas heater of the type that looks like a woodstove.
Assuming equal nominal efficiencies, is the heater likely to be more, less, or equally efficient compared to the insert? It would seem, at first glance, that having all the radiating surfaces inside the conditioned space would increase efficiency, but this may be too simplistic.
Replies
No, it's not really simplistic. Like you said, more surfaces to radiat would be better than having it enclosed in a box. There may be some benefit to the thermal mass of the old fireplace, but that is arguable. You could switch to a direct vent system, too I would think. Vents out the sidewall ... lots of new gas fireplaces do that. I believe they get their combustion air and the exhaust air through a double walled vent device/duct.
Any tall chimney will have a tendency to suck air out of the house ... sealed device or not. Sounds like you have reasonable intuitions in this situation.
We use a free-standing cast iron gas stove (Vermont Castings) for most of our winter heat. Work just fine, looks nice, feels cozy.
I know that the efficiency ratings of both the inserts and the free-standing types are virtually the same--80-83%, but I'm not sure how they're tested, and I think the free-standers are almost certainly more efficient in real-world installations and conditions.
Direct-vent is the way to go, and you can do this even using the existing chimney as a chase in which to run the double pipe that a direct vent needs. DV's can be vented either horizontally or vertically. DV's are safer because the combustion chamber is not open to the room air, and both the intake air for combustion and the exhaust terminate outside in the same pressure zone.