January 2008
Burning controversy
Unvented gas fireplaces can go almost anywhere. But are they safe?
Homeowners who want the warmth of a hearth without the bother of burning wood are increasingly turning to gas fireplaces.
With gas flames that curl around woodlike ceramic logs, these appliances offer a faux fireplace at the click of a switch.
One type of gas fireplace even burns without the need of a chimney or other vent, and so can be installed virtually anywhere. But as it provides warmth and coziness, an unvented fireplace also emits such pollutants as nitrogen dioxide, carbon monoxide, and fine particulates.
Firing up the debate
To shed light on this discussion, we installed and ran two typical unvented fireplaces in our labs. We compared the pollution they generated with the standards for indoor-air quality.
No national standard compels contractors to consider air quality when they install an unvented fireplace; the National Fuel Gas Code and many local codes call only for the fireplace to be sized so that sufficient air is available for combustion. Contractors can, however, use alternative sizing guidelines that consider emissions, drawn up by the Gas Research Institute, an industry group. You’ll find the guidelines here.
We used the GRI guidelines to design our tests of some popular brands of fireplaces. The tests simulated use at an average heat output in the living space of a large home.
None of the fireplaces exceeded guidelines for acceptable levels of carbon monoxide or carbon dioxide, even after many hours of operation. And it took about five hours before a fireplace caused the room to reach GRI's limit for nitrogen dioxide, a gas that's been linked to respiratory problems with chronic exposure at high concentrations. However, an independent review of the guidelines commissioned by New York state recommended that limit for nitrogen dioxide be cut in half. The authors of the guidelines have implied that such a cut is unnecessary and that the lower nitrogen dioxide limit should not be reached, provided their guidelines are followed. Our tests suggest otherwise; we conclude that fireplaces could exceed the lower guideline in a typical home within a couple of hours of operation.
Recommendations
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. That's especially wise if any household member has asthma or another respiratory ailment that may be exacerbated by particulate matter, or if your home is very airtight--and so will disperse the fireplace's emissions less readily.
A vented gas fireplace needn't cost more to buy and install than an unvented model, since some units require only a fairly small vent pipe that runs horizontally to any outside wall.
If you do decide to buy an unvented gas fireplace, here's how to ensure it operates as safely as possible:
One type of gas fireplace even burns without the need of a chimney or other vent, and so can be installed virtually anywhere. But as it provides warmth and coziness, an unvented fireplace also emits such pollutants as nitrogen dioxide, carbon monoxide, and fine particulates.
Firing up the debate
To shed light on this discussion, we installed and ran two typical unvented fireplaces in our labs. We compared the pollution they generated with the standards for indoor-air quality.
No national standard compels contractors to consider air quality when they install an unvented fireplace; the National Fuel Gas Code and many local codes call only for the fireplace to be sized so that sufficient air is available for combustion. Contractors can, however, use alternative sizing guidelines that consider emissions, drawn up by the Gas Research Institute, an industry group. You’ll find the guidelines here.
We used the GRI guidelines to design our tests of some popular brands of fireplaces. The tests simulated use at an average heat output in the living space of a large home.
None of the fireplaces exceeded guidelines for acceptable levels of carbon monoxide or carbon dioxide, even after many hours of operation. And it took about five hours before a fireplace caused the room to reach GRI's limit for nitrogen dioxide, a gas that's been linked to respiratory problems with chronic exposure at high concentrations. However, an independent review of the guidelines commissioned by New York state recommended that limit for nitrogen dioxide be cut in half. The authors of the guidelines have implied that such a cut is unnecessary and that the lower nitrogen dioxide limit should not be reached, provided their guidelines are followed. Our tests suggest otherwise; we conclude that fireplaces could exceed the lower guideline in a typical home within a couple of hours of operation.
Recommendations
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. That's especially wise if any household member has asthma or another respiratory ailment that may be exacerbated by particulate matter, or if your home is very airtight--and so will disperse the fireplace's emissions less readily.
A vented gas fireplace needn't cost more to buy and install than an unvented model, since some units require only a fairly small vent pipe that runs horizontally to any outside wall.
If you do decide to buy an unvented gas fireplace, here's how to ensure it operates as safely as possible:
- Observe the guidelines. Insist that the contractor not exceed them when sizing your fireplace.
- Limit its use. Though occasional extended use of an unvented fireplace should pose little long-term health risk, we suggest limiting operation
to no more than a few hours at a stretch, as a rule.
- Provide extra ventilation. Leave at least one window open in the space where the fireplace operates.
- Buy only a certified package. Some fireplaces are sold as two separate components: a "firebox" and a "logset"--the component that contains the burners
and logs. Ask the contractor to confirm, through the owners' manual or a certification label on the logset from a recognized
organization like Underwriters Laboratories, NRTL, or CSA, that the two components are compatible. A dealer sold us a fireplace
firebox with another brand's logset he claimed was suitable. He was wrong; the combination emitted higher levels of carbon
monoxide than is desirable until we obtained a logset that was approved for that firebox.
- Use a CO alarm. That dealer error aside, the fireplaces we tested showed no propensity to generate any carbon monoxide (CO). Also, some models claim to shut off should carbon monoxide levels ever rise. However, we recommend use of a CO alarm with any combustion appliance, including an unvented fireplace.
