On Wed, 08 Dec 2010 17:40:58 +0000, Maria wrote:

When our heating broke last winter, some kind soul donated a calor gas
heater, but we didn't think about opening a window because it's standing
in an open fireplace.
We spent many hours just dozing off and not knowing why, until we were
told. Oops.

All modern ones will automatically switch off if CO levels get too
high or O2 levels drop too low. (Using a very simply mechanism as
well).

--
Cynic