I have a woodburning stove,8kw,which also heats our water for washing only,for our central heating we have calor gas,
the woodburner is only cost effective because we get our wood for nothing,..i.e.hard wood logs from local tree surgeon and felled Elms that were diseased,...but if we were to be paying for the wood,then it would be a very expensive way of heating the house,
As for the exit height of the flue or chimney,..this has to be above the ridge line of the house, to ensure that the smoke is dispersed by the wind/updraught,if it is lower then it is against building regs,...so,as Colin says,get in touch with building control at your local council ..i,m sure they,ll be happy to help,
Wullie