Rich1028 said:
do they make moisture as well??
When oxygen and gas are burned the byproducts of complete combustion are heat, carbon dioxide, and water. If you look at the flue on any normal gas appliance, you will note a great deal of water vapor coming out of the flue. If you look at a high efficiency furnace, not only is there a large amount of water vapor coming out of the flue, there is also a steady stream being discharged into the condensate line.
There's nothing magical about an unvented fuel burning appliance that makes it any different. Unvented gas heaters are limited by code to the allowable BTU input. The burners are tuned very carefully to insure that they are set up to have complete combustion, meaning if they are working right they don't produce a measurable amount of Carbon Monoxide. They also have oxygen depletion sensors that monitor the ambiant air to insure that the oxygen level is not pulled down by the combustion process. The oxygen depletion sensor will shut off the burner if it starts burning "funny" because the combustion air doesn't have enough O2 in it. They are considered to be 99% efficient, because they burn cleanly and all of the heat they create stays in the structure rather than going up a flue.
BUT...they make water and a lot of it. I've seen cases where people tried to heat their homes with nothing but an unvented heater for a whole winter and it isn't pretty. Drywall falling down. Condensation coating the inside of the windows and pooling on the sills. It's a mold remediation issue waiting to happen.
Unvented heaters are great backup heat if the power goes out. They are great in fireplaces to run a couple of hours a day for extra comfort and ambiance. They are OK to run in a bathroom occasionally to take the chill off. They are outlawed by code in bedrooms. They are easily contaminated by solvents anywhere near them...even a little painting in the basement will cause the upstairs ventless fireplace to emit noxious odors.
They are fine if used as intended but can cause a lot of problems if used inappropriately. I know that heater companies are marketing ventless products for garages. Some people may even have had some sucesss with them. I never have. A "for real" unit heater or wall furnace that includes a direct vent would be a much better choice. A hydronic system would be the ultimate choice.
Phil
