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You are living in a chimney (your house)...

Posted by jb on December 3rd, 2001 01:34 PM
In reply to I have vent-free : no problems at all by BobF on December 3rd, 2001 07:37 AM [Go to top of thread]

anecdote An"ec*dote, n. :
1. A particular or detached incident or fact of an interesting nature; a biographical incident or fragment; a single passage of private life.

an·ec·dot·al (nk-dtl) adj.:
Of, characterized by, or full of anecdotes.
Based on casual observations or indications rather than rigorous or scientific analysis

YOU gave an anecdote, not me. By your anecdotal logic, just because YOU didn't suffer ill effects then no one can or does.

No evidence? Did you read my post, AND the article I gave a link for? It basically rips to shreds the "study" that the Gas industry did to try to con states into accepting the use of these units.

Nevermind that ventless gas appliances aren't even allowed in some states and most of Canada because they are deemed as officially being unsafe (not proved to be always safe).

These decorative units were approved for use WITHOUT adequate testing or institution of pollutant monitoring regimes. You say proof is needed for me to say what I did but there was no real-world study done to APPROVE these devices, so you are the one that is anecdotal. Where is your proof that they ARE safe (in all applications, not just your "anecdotal" little story about your use patterns?

Your pattern of use (an hour or two) is not likely to produce too much moisture or pollutants (maybe - have you measured your NO2, CO and CO2 levels in your house?) CO poisoning is the leading cause of emergency room poisoning cases. Have you had regular maintenance on your unit to prevent incorrect burning? One of the biggest problems is in getting too large a unit and using it for a long time for primary heat needs and not having enough ventilation. In these circumstances an extremely unhealthful atmosphere can be created. The salesmen do not tell anyone this. Basically if the unit isn't sized, used and maintained correctly then there is too high a chance for an unhealthy condition to be created.

Also see page three of:


Some info - especially the links at the bottom of the page, including Consumer Reports article bashing unvented:


Page 5, 5 and 7 (the pdf's pages) of:

Search for Space Heaters in:


The Dept. of energy has studied them and does not like them at all b/c of their potential for harmful pollution:


"An unvented gas fireplace that's safely sized needn't pose any acute health hazard. But our tests confirm that these heaters contribute significantly to indoor air pollution. If you're planning to buy a gas fireplace, a vented model should be your first choice.”


"The data in the AGAR (American Gas Association Research) report on unvented appliances suggests that tighter houses may not be suitable for the installation of unvented products. This is especially true for colder regions of the country, or when cold snap periods are occurring in milder zones"


“Direct vent, sealed combustion models are the only type of gas fireplace we allow in our Health House project."


Building scientists have responded to the gas industry's responses as follows:

• There is little relationship between oxygen depletion and increased combustion pollutants generated by operating a ventless gas heater. While exposure to low levels of combustion pollutants may not be deadly, it can cause ill health effects.

• Manufacturers do not generally include carbon monoxide detectors as safety equipment with ventless heaters. And even though ventless heaters do burn at or near 100% efficiency, it is not unusual for small amounts of carbon monoxide to be generated. Even at non-lethal levels, carbon monoxide causes negative health effects.

• Ventless gas appliances produce substantial amounts of water vapor, which can result in relative humidity levels high enough to exacerbate problems associated with mold, mildew, dust mites, and other biological contaminants. These problems can result in structural damage to a house and adverse health effects to its occupants, including asthma.

The American Society of Heating, Refrigerating & Air conditioning Engineers (ASHRAE) sets a minimum standard for ventilation air in houses of .35 air changes per hour (ACH ). Older, poorly insulated homes easily meet the ASHRAE ventilation requirement (they often have air change rates of 10 or more ACH). However these homes are voracious users of energy and should be tightened up. On the other hand, with recent developments in window and door manufacturing coupled with tighter house construction methods, it is not uncommon for new homes to have natural air exchange rates lower than .1 ACH. These homes should have some type of mechanical ventilation system installed to provide the fresh air required for occupant health.

Important points to consider are these: does the average homeowner know the air exchange rate in his or her house or how to properly size a heating appliance? Probably not. So when consumers purchase and install ventless gas heaters in their homes, they may inadvertently be exposing themselves to relatively high levels of combustion pollutants.

Insulation, weatherstripping, caulking, and annual heating system maintenance can greatly improve comfort levels in a home during the winter months. These measures alone may make the use of a space heater unnecessary. If, after taking these measures, a space heater is still necessary, options exist which are safer than ventless heaters.


Bodzin, S. (1998) "Regulating Ventless Heaters," Energy Design Update, 15 (1), p. 11.

DeWerth, D.; Arono, M.; Borgeson, B. (1998) "Ventless Authors Hot Under Collars," Home Energy, 15 (3), p.4.

Kelly, K. (1998). "On the Havoc Wreaked by Unvented Gas Appliances," Energy Design Update, 18 (1), p.6.

Matson, N. (1998) "How Tight Are America's Houses?" Energy Design Update, 15 (1), p. 10.

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