My whole HOUSE was calculated to need at most 12 kW continuous. The UFH is around 1.5Kw per 30 sq m room. Fully capable of keeping them toasty.
The Aga is 650W continuous and keeps a 30 sq m kitchen more than warm for all but the coldest winter nights.
My old 'Villager' wood burner is in a 30 sq m bedroom and does I think 7 or 8 kW. I do know that about an hour after lighting the otherwise unheated room (although the Aga is underneath it) gets to over 20°C...My biggest problem is trying to throttle it back...
Given reasonable insulation you don't need, at mos,t more than 100W/sq meter for any room, and with good modern insulation 50W is more than enough.
The most pathetic wood burner easily exceeds that.