Kenmac,
We don't disagree about the safety of these devices for occasional attended use as with the use of unvented logs in a fireplace for a few hours at a time. My concerns relate to the use of unvented gas heaters as primary heat sources.
In the case of our TBN colleague greendeere, he is in fact using it as a primary heat source. In fact his heat pump is the back up system and rarely comes on. That means his ventless system is potentially running most of the day (I do appreciate we are talking about Georgia but this time of year I assume y'all run heat full time as we Yankees do). That was not what these devices were designed for and frankly they have never been subjected to the sorts of longer term real world scientific testing to insure that they are safe in such circumstances. Most of the testing done to certify these vent free devices look at one hour of use or sometimes up to 8 hours but there really are no independent studies looking at one heating season for example.
You point out that most people don't have their gas furnaces inspected annually. You are correct, but any noxious compounds that occur due to malfunction of those units literally goes out the vent/chimney. In the case of ventless products those same compounds go into your house.
Additionally, from "ventfree.org" the industry lobby group's own website:
- What maintenance is needed on vent-free appliances?
- As with all gas appliances, vent-free appliances should be inspected for proper operation at least annually by a qualified service agency. The burners should be visually inspected and cleaned in accordance with the manufacturer's instructions.
Not bothering to inspect a vented appliance may result in less efficiency than desired but is unlikely to result in toxic gases being discharged into the home. That cannot be said for vent free devices.
The concern with ventless products is not that they are going going to explode and they may well not be an oxygen depletion risk with the ODSs but they certainly have the potential to add noxious undetectable (to human nose) air pollutants which could affect human health. That is why Canada and European countries have not allowed them. The USA as we all know has a political system that is quite vulnerable to special interest lobbys. The GAMA (Gas Appliance Manufacturer's Association) is an industry interest group not a professional scientific body. The GAMA doesn't recommend them as primary heat sources yet they really don't do much to discourage the devices from being used that way. As they are by far the cheapest and technically most efficient heaters on the market, it is obvious that some people will bend the rules and use them as a primary heat source. Where is the GAMA or Ventfree Gas Products Alliance marketing campaign to discourage such use? Their promotional material all carefully states these heaters are for "supplemental" heat only yet they are selling a million units a year and it is perfectly clear that many of those units are functionally primary heating sources especially for the poor in the southern parts of this country.
From the Centers for Disease Control, Atlanta (MMWR
46(51);1221-1224)
Since 1992, use of unvented combustion heaters has increased because in many states, regulations prohibiting the use of these devices have been rescinded. As of November 1997, five states prohibit the use of unvented gas-fueled or liquid-fueled heaters (Alaska, Massachusetts, and Minnesota; and Colorado and Utah at high altitude only) (M. Carson, Vent-Free Gas Products Association, personal communication, December 2, 1997). Manufacturers recommend that these devices be used for short periods of time with a nearby window open for ventilation (5; M. Carson, Vent-Free Gas Products Association, personal communication, December 2, 1997). Failure to follow these instructions could result in elevated levels of combustion by-products.
Both unvented and vented heating appliances must be properly maintained to reduce the risk for associated health hazards. Persons who use unvented combustion space heaters should follow manufacturers' recommendations and use these devices only for short periods in well-ventilated areas to prevent the accumulation of toxic gases in living spaces. Other prevention strategies include conducting media campaigns detailing the potential hazards of unvented combustion space heaters during the colder months and encouraging the proper use of CO detectors in homes.
Finally, for someone with a "tight" house, as greendeere describes, the ventfree.org people recommend that additional steps be taken to provide fresh air. From their website:
In tightly constructed homes, additional provisions for combustion and ventilation air must be provided using one of the methods defined in the National Fuel Gas Code, ANSI Z 223.1/NFPA 54 For example opening a window which certainly decreases overall heating efficiency calculations though the industry lobby group never bothers to point that out.
in the living space (or in the house)