Maybe 50 sq. meters (150 sq ft.?). Our only heat soure is a Jotul F100. You can't find a smaller stove, yet it keeps us warm. Maybe too warm. My problem is that when it comes time for bed, I've burned on low for so long, I don't have enough coals to sustain a decent burn through the night. How can I keep us at a decent temp through the evening and still maintain a good burn through the late hours? I've somewhat resigned to the fact that mornings will be cold, but the Mrs. insists there's a better way.