something on the topic "...there are few choices for stoves / fireplaces with so little power...", quite simply: Just put one piece less wood on... The manufacturers' specifications refer to the maximum possible power, which (among other things) depends on the amount of wood to be burned in the combustion chamber...
It’s very clear to me personally. I know from training how such a device works...... .
I wrote: Stoves in that class are rare. But there are some, say one with 4.5 kW. You can then also regulate it down with less wood. Mine has a specified range of 2.7-9 kW. I thought back then: Great cute little thing, though low power, but when I bought it, I had no idea how little the house needs....
But you have to heat up the unit first so that clean embers develop and afterward, when adding wood, clean combustion (flame pattern) occurs.
In my house, it’s already warm on the ground floor afterward..... after 35 minutes.
Even VERY sparingly adding wood (I guess factoring amount, efficiency, and so on the thing then runs at about 2 kW, otherwise it goes out or the flame no longer fits, too little oxygen/material) it gets too warm. Well. For me there is no too warm as long as it’s under 35 degrees. But ask my wife at 23.5, what she says about the topic then. .
No wonder it gets warm. The heating also runs at -5 degrees with 3 kW. But not continuously. P_eff = approx. 1 - 1.5 kW for the whole house. That in a KFW-70. Put this burner into a 55 or 40. You don’t need a sauna anymore – then everyone sits naked at the fondue in the living room...... . And it’s almost irrelevant whether the area is 69 sqm like ours or, as in a typically sized house today, 85 or 100.
Regards
Thorsten