We have heated our 2000 square foot house for ten years with a single unvented gas heater. For most of those years, it sat on the fireplace hearth. I kept wanting the damn thing to malfunction, so I could replace it with a gas-log set.
Well, this year, it happened -- a malfunction good enough for me to get the "ventless gas log heater" (as they call them around here.
The view is beautiful -- logs glowing with incandescant red heat in the midst of it, and cheery dancing flames of yellow. I expected that it would put out somewhat less heat than our previous unit. But, no -- it can make the entire house oppresively hot if we don't crack some windows on opposite sides of the house to pull in a bit of cold air from outside. A few times, I've opened the front and back doors wide open to get a quick cool-off.
These things put out Mucho Calories of heat. Hot, hot, hot. And still their the prettiest things I've set eyes on.