Incredibly inefficient - not
We have a circa 1950 Rayburn version of the AGA. It was solid fuel but converted to oil. It heats a > 400 year 3 bed house and provides hot water for less than £500 a year. Not on all day. We once left a roast lamb dinner it it when we went to a beer festival. We were 3 hours late home and the lamb was delicious. If they are used properly can be a great asset.