“Main source?? Somehow I doubt that.”
Really? You doubt it why? It’s the main source in our home in South-Western Virginia. We have a small kerosene monitor in the kitchen and wood stove in the living room. That’s it...and our small log home stays so warm we turn the monitor off a large percentage of the time.
I have a masonry fireplace in my house. The best I can say of it is that it greatly reduces the load on the main central heating unit. If it was the “main” heating source in the house, there’d be some might cold rooms.