We have a clean air approved log fire which is not on wet back but can boil a jug, perc coffee and/or make soup/stew. It is hard to get a wet back log burner with a wet back because a very efficient wet back takes too much heat out of the combustion chamber and makes more polution. So called wet backs are only boosters and don't boil the hot water system like the caste iron ones in the fire place in grandads day. You can sometimes install a system of ducting and a fan to take heat from the flu and direct it towards other rooms. Most log burners have double or triple skins on the flue for fire protection and the heated air between the skins is normally wasted and exited to the outside air.