Unvented heater/ODS info

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

The t-couple on a ODS equipped heater is a standard one. The difference is the orifice that leads to the actual pilot. The orifice actually is a specific size that a certain amount of oxygen goes through to keep the pilot burning. If the oxygen content drops too low, the pilot 'impinges' on the t-couple less, effectively killing the power generation.

What kills more people, freezing to death/exposure, or unvented gas heaters?

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