On Tue, 10 Oct 2006 22:08:15 -0400, "HeatMan"
wrote:

First off, unvented heaters make people into Darwin award nominees (They
kill people).

Why do you say that?

Here in Connecticut there are thousands of unvented heaters in use.
They all have oxygen depletion shutdown systems and other safeties
that are reliable. They have UL and American Gas Association safety
ratings. The codes only prevent them from being used in enclosed
bedrooms, probably worrying about oxygen depletion.
The O2 sensors in ones that I've seen shut down the heater if the O2
is reduced from the nominal 22% in air to 19%.

Unvented gas fireplaces are also increasingly common.

Consumer reports did an analysis of them. The CO emissions were
miniscule. They did wonder a bit about the amount of water vapor
emitted into the air - possibly a problem for mold growth under
certain circumstances. Yet the addition of moisture in the air is
generally a good thing during winter.

I've not heard of a single death from one of these units.

I have heard of deaths from malfunctioning standard vented gas
furnaces, boilers and heaters.

Doug