We have a multi fuel burner in the dining room (our living room really) which heats 7 radiators and the water. In the lounge we have an open fire
In terms of energy efficiency, it’s a bit like a car; it depends on the make, model and condition. We’re on our second wood burner because we were burning more than 8 tonnes of wood each season and even then the house wasn’t particularly warm.
We have a new model now which kind of ‘reburns’ the smoke to get every last drop of energy from it (it also means you can use it in a smokeless zone, which is utterly amazing). It certainly IS more efficient but I don’t know by how much as we’re not yet through the season. The water that comes out of the tap is almost at boiling point, we have a safety radiator and although the house never gets hot, it’s comfortable.
In terms of cost, it’s only cheap for us if we get access to free wood. If we have to buy it in, then forget it. A nice load of ash is £80 and that lasts 2-3 weeks depending on weather conditions and whether we keep the fire in at night time.
If you’ve got a source of fuel however, it’s brilliant. THis year all our wood has required our time and effort but no money, so I’m sitting here this year with free heating and hot water - bliss! Other years we’ve run out of wood and frozen our arses off by the end of Feb and it’s not nice…
So the upshot it, in my opinion, you need to find out more about the fire - how old is it, what is the BTU, how many radiators does it run, how big is it, how giv is the room it is in, what is the make and model. I think it’s nice with the Aga too because you could use that solely for water and use the solid fuel burner for heating. Also, is it multi fuel, or a wood burner? I don’t like to do it, and probably should’n't admit it, being a greenie and all that LOL! BUT I have burned anthracite on ours when it’s been super cold; just to keep it in at night; otherwise the temp in the house drops down to 15 which is too cold for my comfort levels.
This probably hasn’t answered your question at all, but hopefully it’s given YOU some more questions to ask so you can make an informed decision.