Here the main house is from the late/early 50s if I remember correctly. Is a prefab. Early 70s my wife's grand parents bought it used moved and installed it here. From there, they did additions and when they did used better insulation on those additions added over the years, it is far from modern times. Many parts are not even insulated. 80% of the part of the house facing North is the main house that has like newspaper for insulation in the walls.
On the last 2 years I have been doing some remodeling but still far, far, far from be perfect and never will. It is what it is.
The whole point is that I have no issues keeping the house to a decent temperature with one of the BK when I did the switch. The house still on a bad shape and leaky as hell at that time. I really don't know what to say.
@bholler for long time without burn on one, you have that negativity that a BK will not heat your place. Possibly you just have that in your mind. Everything is possible, but anyway it has been said so many times here, what work for some, don't work for others.