I remember when I first got my license (about an hour ago) asking the instructor why a gas stove didn't need to be vented. He couldn't come up with an answer. I have attended a few emergency calls that involved CO detectors being activated by stoves. It's usually the homeowner boiling water for hours on end in a large pot, like when making tomatoe sauce in the fall. When a flame impinges on a cold surface, walla! These non-vented heaters aren't "special"....the people who buy them are.
I never endorsed nor would I ever install a ventless heater for myself.
On the other hand I have never smelled the "stink" that "smells like [I] am using a kerosene heater" even when running a 30k BTU oven and three
15k BTU burners for hours. My family does not suffer from headaches or breathing problems when cooking for hours.
Burning natural gas just doesn't smell like kerosene. If its burning properly there is no (human) detectable odor. If someone (like you) wants to say an unvented natural gas appliance adds unwanted water vapor as well as potentially harmful combustion byproducts to the living space, I'll agree.
If a poster says it smells like kerosene and will at a minimum give everyone headaches and breathing problems, I'll happily imply that the poster is spreading misinformation and hope that no one believes anything they say on the subject.
The current unvented heaters with O2 depletion sensing pilots have over a
40 year track record of safety in Europe. CO has not proven to be an issue with real data.
Nuisance outages is real issue particularly at higher altitudes where O2 is depleted!
Most states require they only be used for supplemental heat or decorative use.
MA was one of the last states in the US to approve unvented gas heaters. Unlike 48 states, MA added the requirement of not only an O2 depletion sensor but a hard wired battery back up CO detector in each room such a heater is installed, (the hard wire requirement is new).
Now if someone could provide credible references of a properly installed and inspected O2 depletion sensing heater causing hazardous CO, please post it!
Air quality is a different topic and may depend upon what sensitivities an individual has. Some states such as ME (Maine) require ERV in every new home or with any new heating system. That does a lot for air quality.
RE CO, I'd personally worry more about a faulty furnace's combustion products than a properly installed unvented heater.
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