> Most of the heat from a fireplace goes up the flue unfortunately. Depends on the fireplace. Direct-vent gas fireplaces take outside air for combustion and th

> Most of the heat from a fireplace goes up the flue unfortunately. Depends on the fireplace. Direct-vent gas fireplaces take outside air for combustion and then exhaust it, with no inside air being used in the process. There are also direct-vent wood stoves that can do the same. Wood stoves can get about 85% combustion efficiency, but that's not heat-delivered efficiency (often 10-20% lower): * https://www.epa.gov/burnwise/energy-efficiency-and-your-wood-burning-appliance#measured https://www.epa.gov/burnwise/energy-efficiency-and-your-wood...