I should have been more clear: I am talking about heating water and/or food, not the entire house. We live in a fairly typical suburban four-bedroom house without natural gas or a fireplace. I figured since natural gas is considered relatively safe for cooking, there may be others that are reasonably safe as well (recognizing that burning anything involves some risk). We do have two battery-powered CO detectors, but I would not like to find out the hard way that I shouldn't have been burning (fill in blank) to heat some water.

I had also considered MRE heaters and wondered how effective and safe they are. I realize that they can be more expensive to use, but that's all right for my needs.

Thank you all for you input.