use non-oxygon consuming heating, like chemical heating pads and if you want to warm food use chemical heating pads like supplies with MRE"s
Ouch! Be careful. MRE heaters usually have instructions warning against using too many in a HMVEE, tent or other enclosed non-ventilated area due to the (non-breathable) hydrogen (I believe?) they give off. Using these in a sealed room is not a good idea. <img src="images/graemlins/tongue.gif" alt="" />
As for chemical heaters, there are some which begin to warm up merely upon contact with air, as soon as the package is opened. These contain iron which oxidizes rapidly, releasing heat. They last for hours, which is great, but they require oxygen because they use it up. <img src="images/graemlins/frown.gif" alt="" /> When oxidation happens fast enough, we call it flame. When it is very slow, we call it rust. When it happens fast enough to release heat, but not fast enough to release flame, we call it a really cool effect of modern chemistry which lets us make nifty hand & body warmers. But no matter what, it is oxidation and that means it is using up the oxygen by binding it with something, in this case iron. And yes, it gives off CO, just like flame, though perhaps less? (I don't know.)
The only chemical heaters I know of which would be safe are the reusable gel-filled heat pads that have a small metal disc in them. The disc is slightly concave/convex and you "pop" it by pushing it to be convex/concave (the opposite way). The shockwave created in the gel by this kinetic pop causes the gel to begin to crystalize rapidly. As it does, it gives off heat. Once solidified, it ceases to give of heat. You can return the crystalized gel to a liquid state by boiling the gel-pack for a little while. They are good for many repeat uses. The chemical reaction in these types of heaters does not involve oxidation and does not use up any oxygen. The problem with these is they last a half hour or so. <img src="images/graemlins/frown.gif" alt="" />
The best way to stay warm in such a situation might be to somehow filter your central heat air. That may take more engineering and construction than many of us would likely be willing to devote to it. The next best way might probably be to snuggle up with your loved ones under some blankets. Come to think of it, maybe that's
the best way.