If I do not have a bad shot, you should be to asking common and fuliginous furnace and furnace of earthy central heating which more expend coal or more save coal! The answer is earthy warm furnace apparently more cost coal. You think earth warms a furnace wants those who offer a few rooms to make warm, do not burn not hot, burn have to keep coal! And common and fuliginous furnace is much more optional, a room a furnace, the area that make heat is small, temperature promotion is fast! Do not heat up coal get angry, temperature is elevatory and OK fire
