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Hearth & Home September 2014

Natural gas pipeline at sunset.
Cover Photo: Mendota ML47.

Gas: Heart of the Hearth

By James E. Houck

This is the first of a three-part series on gas-fueled appliances in the residential hearths of North America. Gas-fueled appliances are one of the more important product categories produced by the hearth industry. The articles will look at both positive and negative market drivers, socio-demographics, regionalism, environmental issues, regulations, certification requirements, manufacturers’ perspectives and consumer attitudes.

Four million is a big number. Eight million is also a big number. Twenty-eight million is an even bigger number. While these numbers seem as if they should belong in the realm of astronomy, such as the distances in miles to near earth-crossing asteroids or to Venus in a particular orbital position, they are not only astronomical but are also grounded in the hearths of our homes.

For the North American marketplace, four million is the approximate number of gas log sets manufacturers have shipped in the past 10 years. Similarly, eight million is HPBA’s 10-year tally on the number of gas appliances (fireplaces, freestanding stoves, inserts, plus vent-free fireboxes) that have been shipped in the same time period. Twenty-eight million is the survey-based estimate of the total current number of gas-fueled fireplaces in North American households.

Even wood-burning fireplaces are part of the gas picture. In addition to the 28 million gas-fueled fireplaces – based on U.S. Census Bureau, American Housing Survey and HPBA survey data – there are another 16 million wood-burning fireplaces in North American homes. According to HPBA’s consumer research, 24 percent of wood-burning fireplace owners have considered converting them to burn gas, and many already have done so, as reflected in that fact that 23 percent of existing gas-fueled units were once originally wood-burning. Many wood-burning fireplaces also regularly use some gas due to the ubiquity of gas log lighters.

Sometimes it’s easy to forget that it’s not just the direct manufacturers, distributors and retailers of gas fireplaces, gas inserts, gas stoves or gas logs that are impacted by the demand for new gas units. A host of gas-related products with their infrastructure of manufacturing, sales and installation networks are also impacted. For example, venting systems, glass doors, gas plumbing components, thermostats, and replacement parts are all tied to the magnitude of gas fireplaces and stoves sold and in use.

Housing Starts and Completions,
1 Unit Structures, Rolling 12 Months

Construction of new single-family homes is on the upturn but there is still a long way to go to reach 2005/2006 levels.

New Home Construction

As everyone in the hearth industry knows, construction of new single-family homes is the key market driver for fireplace sales. Over the last decade more than half of newly constructed single-family homes have had one or more fireplaces installed. Year-to-year this fraction has been fairly constant and there is no reason to expect it to change.

While the number of new single-family houses completed in 2013 was down from the 2006 peak of about 1.65 million annually, there were still 569,000 new single-family houses completed in 2013; with the improving economy, projections are for housing construction to eventually recover, albeit with “fits and starts.” It should be noted that a smaller but not insignificant number of fireplace sales (estimated at about nine percent) are for use in remodeling of single-family homes, and also about 6,000 fireplaces went into units in new multi-family buildings in 2013. Both of these smaller markets are also predicted to increase with a projected improved economy.


Fuel cost and availability historically have been market drivers for the home heating industry. Case in point is the replacement of coal with natural gas as the dominant national home heating fuel in the 1950s and 1960s associated with the development of the natural gas network. While it’s fading in our memories, in 1940 more than one-half of the households in the United States used coal as their main heating fuel; now it’s less than 0.2 percent.

Replacing coal as the main heating fuel, more than half of the households now use natural gas as their main heating fuel. Similarly, but more recent and perhaps still in most of our memories, was the heyday of wood stove sales in the late 1970s and 1980s due to the high cost of fossil fuel and consumer concern over its future availability. Both scenarios are dramatic testaments of the impact of fuel cost and availability on consumer purchasing decisions.

In common residential usage the following are synonyms or nearly equivalent terms

Natural gas = utility gas = piped gas

Liquefied petroleum gas = LPG = bottled gas = propane = LP (residential LPG is mostly propane)

1 cubic foot (cf) of natural gas = 1,027 Btu

100 cubic feet (Ccf) of natural gas = about 1 therm = 100,000 Btu

1 gallon of LPG = about 94,475 Btu

Eighty-seven percent of U.S. gas fireplaces are fueled by natural gas. Thirteen percent are fueled by liquefied petroleum gas (LPG). About half of the LPG in the U.S. is derived from natural gas sources and about half is derived from petroleum refineries. America’s petroleum production that had been declining for the past 40 years is back on track and America is now projected to be the world’s largest producer in 2015, with U.S. crude-oil production expected to be at the highest level since 1972.

Part of this dramatic increase is due to fracking technology. Fracking produces a shale oil that has been referred to as “ultralight” or “gassy” oil, meaning it has a high fraction of volatile compounds that are in part what makes up LPG. Consequently, there should be a lot more LPG domestically produced in the future.

Similarly, daily natural gas production grew by five percent over the past year and is expected to continue climbing with the U.S. becoming a net exporter by 2018. In summary, these facts suggest that, while weather, the delivery infrastructure and the possible impact of exports on the domestic market can all affect availability and price, if all else is equal, more and lower-cost natural gas and LPG should become available.

About 61 percent of U.S. households report using natural gas for home heating, cooking and/or for other appliances. Roughly 10 percent more households report that natural gas is available in their neighborhood but they do not use it. An additional eight percent of U.S. households report using LPG. Not surprisingly, LPG is more dominant in rural areas where the natural gas delivery system does not reach.

Together, households that are already hooked up to use either natural gas or LPG make up over two-thirds of U.S. homes. These homes are either direct candidates for the installation of a new gas fireplace or stove, or if they already have a gas fireplace or stove installed, they may provide sales opportunities for replacement components, replacement units, gas log sets, inserts or accessories.

Further, it’s reasonable to expect that new single-family houses that are the big market for new fireplaces will be hooked up for gas at about the same proportion as existing houses. With this being said, there is regionalism in market potential. Certain states, such as some New England states, have more limited natural gas service and accordingly provide a less attractive marketplace for gas appliances. In contrast, states such as California and Illinois, with their large populations and with high fractions of homes with gas hook ups, offer more potential for sales.

10-Year Natural Gas Prices

Natural gas prices are now reasonable. Graph shows natural gas 10-year U.S. consumer price index trend (average price data). Dollars per therm. Bureau of Labor Statistics.

10-Year LPG Prices

LPG prices have slowly increased in the last 10 years with a significant spike last winter due to the extremely cold weather in the Midwest and East. Graph shows 10-year trend of weekly U.S. residential LPG prices in dollars per gallon. DOE data.

Future Regulatory Hurdles

It’s not unexpected, and in fact reasonable, that appliances that involve high temperature combustion in residential settings, that produce air emissions, and that consume energy are subject to governmental regulations. There are current testing protocols in place that satisfy federal, state and local requirements addressing these safety, health and energy issues which already represent a considerable cost burden to manufacturers. They include an alphanumeric soup of certification test methods such as, ANSI Z21.50, ANSI Z21.60, ANSI Z21.84, ANSI Z21.88, ANSI Z 21.11, RGA 2-72, UL 307b, CSA P.4., and AFUE (DOE 10 CFR Pt. 430).

However even beyond the considerable number of certification tests with which specific gas appliance types need to comply, there has been a recent flurry of new regulatory activities that may provide future hurdles for manufacturers – potentially reducing margins and reducing the size of the marketplace. Most notable of these have been: (1) The U.S. Department of Energy’s attempt to regulate efficiency of all gas-fired appliances, notably including decorative fireplaces. (2) The Consumer Protection Safety Commission’s effort to reduce injurious burns from hot glass surfaces on gas hearth appliances. (3) Natural Resources Canada’s revision of the P.4 efficiency test for gas hearth appliances. (4) California’s Title 24, Part II Net Zero that will require, as of Jan. 1, 2020, all newly-constructed residential homes and commercial buildings to create with on-site sources as much energy as that structure consumes on an annual basis.

1. U.S. Department of Energy’s (DOE) attempt to regulate the efficiency of all gas-fired hearth appliances including decorative models.

Unlike natural gas that is transported through pipelines in the gas phase, LPG is transported under pressure in the liquid phase and then volatilizes in residential tanks for use as a gas.

After the DOE in 2011 and 2012 issued proposed rules that would have classified decorative hearth products as direct-heating equipment, the Hearth, Patio & Barbecue Association (HPBA) and the National Propane Gas Association (NPGA) sued the DOE in Federal court. On Feb. 8, 2013, the HPBA and NPGA won that lawsuit, barring the DOE’s new regulations from going into effect on April 16, 2013, and requiring the DOE to either appropriately define “vented hearth heater” to exclude decorative products, or to come up with a new covered product category if the agency sought to regulate decorative products.

The DOE on Dec. 31, 2013, issued a new Proposed Determination of Hearth Products as Covered Consumer Products to cover all gas-fired hearth appliances including vented and vent-free, and decorative indoor and outdoor hearth products – anything with an exposed gas flame. The DOE defined a hearth product as a “gas-fired appliance that simulates a solid-fueled fireplace or presents a flame pattern, for aesthetics or other purpose, that may provide space heating to the space in which it is installed.”

The DOE says further that the “proposed definition includes, but is not necessarily limited to, all vented and ventless hearth products” that could include decorative hearth products, gas logs, gas stoves, outdoor and vent-free hearth products – possibly even gas grills. The HPBA feels this is an effort by the DOE to gain coverage over as many products as they can while not revealing the regulatory requirement details of its proposal.  

The HPBA has commented that the DOE’s definition is overly broad and lacks the regulatory detail to allow interested parties to make fully informed comments on the rulemaking. Reacting to the Feb. 8, 2013, court decision, the DOE on July 29, 2014, published a final rule removing the definition of “vented hearth heater” and the related energy efficiency standards for heater-rated vented gas fireplaces.

This final rule also removed the Annual Fuel Utilization Efficiency (AFUE) values from the earlier rulemakings since the AFUE now applies to no category of products after the definition of “vented hearth heater” was stricken.

Decorative hearth products have been “officially removed” from the DOE’s rulemaking, but the HPBA is concerned about the DOE’s future attempts to cover additional products.  

With no timetable for the next steps in the rulemaking, the HPBA is strategizing its proactive approach with manufacturers and interested parties. In the meantime, the DOE, through its contractor Navagant, is surveying hearth products manufacturers to gain data on engineering specifications of products of the same current aesthetics while using less fuel, as well as industry market information and future market speculation. The HPBA expects the next step by the DOE perhaps in the first half of 2015.

Percent of Households Heated by Natural Gas

The percentage of households that use natural gas varies from state to state primarily due to the extent of the natural gas distribution system and climate. The data are for home heating use of natural gas in 2000.


Due to limitations in the natural gas delivery network, natural gas is used more frequently in cities, towns and suburbs whereas LPG is used more in rural settings. Data from U.S. Census Bureau American Housing Survey.

2. ANSI/CSA standard for gas hearth appliance glass barriers – An effort to reduce the possibilities of injurious burns from hot glass on gas hearth appliances.

Example efficiency rating label for fireplaces to be sold in Canada.

Action was originally prompted by the Consumer Protection Safety Commission (CPSC), but on April 23, 2013, a petition requesting the CPSC to require safeguards was denied by the CPSC because it recognized and supported the hearth industry’s efforts to create a new requirement to existing standards.

The new requirement specifies a “barrier” on the glass front of any gas hearth appliance whose glass temperature exceeds 172 degrees F., the current standard for ovens, for any product manufactured after Jan. 1, 2015. Decorative elements on the barrier cannot exceed five percent of the surface area of the barrier and are limited to a width of ¾”. Some manufacturers are using or plan to use double glass and/or an air wash as their barrier to reduce glass temperatures.

Besides a “hot glass” warning label, manufacturers will be required to supply, but not necessarily install, any barrier. However, the barrier must be in place when the appliance is installed, obligating the product installer to ensure the barrier is in place. There is no requirement that the barrier must remain in place after it is installed.

Manufacturers and retailers can continue to sell models without barriers produced prior to Jan. 1, 2015.

This requirement for a barrier is an addition to ANSI/CSA Z21.88 for heater-rated gas hearth products and ANSA/CSA Z21.50 for decorative gas hearth products.

2013 Building Energy Efficiency Standards

Part 6 of Title 24

Section 150.0 – Mandatory Features and Devices Installation of Fireplaces, Decorative Gas Appliances and Gas Logs

“1. If a masonry or factory-built fireplace is installed, it shall have the following: A combustion air intake to draw air from the outside of the building, which is at least six square inches in area and is equipped with a readily accessible, operable, and tight-fitting damper or combustion-air control device….”

2013 Green Building Code Standard

Part 11 of Title 24

Section 4.503 Fireplaces

“Any installed gas fireplace shall be a direct-vent, sealed-combustion type.”

3. Canada’s P.4 Efficiency Test for Gas Hearth Appliances

Manufacturers must test to P.4 and advertise results to consumers.

Natural Resources Canada (NR Can) proposed a review of the P.4 test developed in 2009, a proposal supported by the HPBA Canada. NR Can requires gas hearth appliance manufacturers to test to P.4 and to advertise to consumers the efficiencies of its gas hearth products. It does not require minimum efficiencies.

This current review has corrected flaws in the test formulas and clarified test protocols that were originally based on a test method and standard for gas furnaces. Decorative products are covered, but not gas logs.

The Canadian Standards Association’s (CSA) technical subcommittee has completed its review and is reviewing public comments. It was decided that minimum efficiencies will not be required because it is not known how gas hearth appliances are used in the real world. NR Can is planning to conduct a field survey of consumers to determine how these products are actually used. The survey may include in-house monitoring during the heating season.

A revised version of P.4 is scheduled to be published later this year or early 2015.

4. California’s Net Zero
(Title 24, Part II)

Part of the California State Building Code, it restricts gas hearth appliances to direct-vent models.

In Net Zero, an extension of the separate Energy Code portion of Title 24, the goal of the California Energy Commission is that, as of Jan. 1, 2020, all newly-constructed residential homes and commercial buildings must be able to create, with on-site sources such as photovoltaics, as much energy as that structure consumes on an annual basis.

The HPBA Pacific affiliate has succeeded in getting zone heating to be recognized in the current California Energy Code as a crucial first step for including gas hearth products in the critical energy calculations for Net Zero.

Also in California, the state’s Green building code, Cal Green, mandates only direct-vent gas products.

The Absurdity of DOE’s Actions

Ostensibly, the purpose behind DOE’s activity has been energy conservation. Perhaps the most damaging outcome for the hearth industry would have been the requirement for decorative vented gas fireplaces and gas log sets to have unrealistic efficiencies. The absurdity of DOE’s actions can be illustrated using very sound data. Data show that decorative vented gas fireplaces would be projected to use only about 0.06 percent of the total gas used in the U.S. by 2020 and gas log sets would use about 0.16 percent, or together about 0.22 percent.

A requirement for increased efficiency would not do away with all that energy but would only increase average efficiency by maybe 20 percent. The energy at stake then becomes (20% of 0.22%) about 0.044 percent of the total amount of gas energy used in the U.S. Further, any new DOE regulation would have only applied to new units. To get the full 0.044 percent gas savings, not only would all future new fireplaces and gas log sets that were sold have to meet the DOE regulations, but all the old fireplaces and log sets would need to have been replaced with new ones meeting the new DOE standards by 2020.

Additionally, history has shown that consumer demand for the aesthetics and the warmth of fireplaces is unlikely to disappear, so if decorative gas fireplaces or gas log sets become less available, less user friendly or prohibitively expensive due to the DOE action, it’s possible that solid-fuel fireplaces, electric fireplaces or the inappropriate use of heater-rated gas fireplaces will fill the void. All would use roughly the equivalent or even more energy than a typical decorative vented gas fireplace or a gas log set.

Projections show that, at even current efficiency levels, decorative vented gas fireplaces would represent only 0.06 percent of the total U.S. natural gas and LPG consumption in 2020. Similarly, gas log sets would represent only 0.16 percent. All percentages are the percent of the total U.S. natural gas plus LPG consumption. Data from U.S. DOE and U.S. Census Bureau reports.

Projections for new fireplaces are based on 10-year average (2004-2013) HPBA shipment records and the assumption that the relative proportion of the various gas fireplace categories will remain constant.

*The other residential gas appliance category shown in the graph includes clothes dryers, space cooling appliances, outdoor grills, exterior lights, pool heaters, spa heaters and backup electricity generators.

Air Emissions As a Market Factor

Air emissions can influence the type of fireplace that a consumer chooses. Consumer perception of environmental and health risks associated with fireplaces can be gained either from the media or from direct experience. Some air quality jurisdictions make the choice for the consumer by outright banning or limiting the use of certain fireplace types. There are three general categories of air emissions associated with residential gas appliances. These are: (1) Greenhouse gases, (2) Air emissions emitted to the indoor environment, and (3) Health injurious air pollutants emitted to the outdoor ambient air.

1. Greenhouse Gases

Carbon dioxide and methane are the two greenhouse gases of concern from gas appliances. Carbon dioxide is produced by the complete combustion (oxidation) of carbon containing fuel. Methane emissions can either be from the incomplete combustion of carbon containing fuel or, more significantly, from direct leakage of natural gas

(natural gas is about 90 percent methane.). This leakage can be from the appliance, from associated in-home gas plumbing components, and from the gas transmission network.

Natural gas, when burned, emits lower quantities of carbon dioxide per unit of energy produced than do other fossil fuels, so it’s an attractive fuel choice among fossil fuels. For the major fossil fuels, the amounts of carbon dioxide produced for each billion Btu’s of heat energy extracted are: 208,000 pounds for coal, 164,000 pounds for petroleum products, and 117,000 pounds for natural gas.

However, unlike carbon dioxide from fossil fuel combustion, the carbon dioxide produced by biomass combustion, such as cordwood in a fireplace, is not considered by most to be a greenhouse gas because, simply put, biomass combustion does not introduce ancient carbon into the atmosphere but only cycles modern carbon between the biosphere and the atmosphere.

So, on the basis of direct carbon dioxide emissions alone – at first glance – it seems as if wood-burning fireplaces would be a better choice than gas fireplaces to minimize climate change impacts – but it’s not that simple.

As noted, the major constituent of natural gas is methane. Also as noted, methane directly contributes to the greenhouse effect through venting or leaking of natural gas into the atmosphere. Methane is 21 times as effective in trapping heat as is carbon dioxide. Because of methane’s higher greenhouse gas potential, although U.S. methane emissions amount to only 0.5 percent of the U.S. emissions of carbon dioxide, they account for about 10 percent of the greenhouse effect.

The complete combustion of natural gas that is typically about 90 percent methane (CH4) produces carbon dioxide and water. Carbon dioxide (CO2) from gas fireplaces has two issues: (1) Globally it is the most significant greenhouse gas and (2) Indoor elevated carbon dioxide concentrations are well known to induce drowsiness. Water vapor is not an issue when vented outdoors but its condensation indoors from vent-free appliances has been a point of controversy.

Twenty-one percent of the total national man-made emissions of methane are from losses in the natural gas delivery system. For about every 60 molecules of methane that reach a residence for use in a fireplace, about one molecule of methane is lost along the way. This is not surprising when one considers that there are: (1) an estimated 272,000 miles of 20- to 42-in. pipe making up the transmission system, (2) there are compressor stations about every 50 miles, (3) there are gathering systems, (4) there are gate stations, (5) there are local distribution systems, and (6) there are service lines to each home.

Further, there are innumerable valves and flanges along the way. The greenhouse impact from this fugitive loss of methane is on the same order of magnitude as the greenhouse impact from the carbon dioxide produced by the natural gas combustion in the home. So, again on first glance, it seems as if wood-burning fireplaces would be a better choice than gas fireplaces to minimize climate change impacts – but again it’s not that simple.

Methane is also significantly produced by incomplete wood fuel combustion. Among all stationary point sources (a.k.a. smoke stacks and chimneys) sources of energy production that notably include electricity generation, energy production in industrial facilities, energy production in commercial facilities, and residential sources of energy, the U.S. EPA attributes an astounding 59 percent of the methane emissions nationally to residential wood combustion. (But is this factual?) Unlike carbon dioxide from biomass combustion, methane is not considered greenhouse gas “neutral,” and emissions of methane from wood-burning fireplaces do contribute to climate change.

Finally, to add to wood-burning fireplaces’ climate change woes, black carbon, which is in particulate matter emissions from residential wood- burning, has been implicated in climate change. Soot, a.k.a. particulate matter, from wood-burning, has a highly absorbing black component which is variously called “elemental,” “graphitic” or “black carbon.”

Measurements have shown that, depending on burning conditions, 10 to 30 percent of the particulate material from cordwood stoves is made up of black carbon. Similar percentages would be expected from wood-burning fireplaces. (Soot is also produced from the residential combustion of natural gas and LPG but in much smaller amounts than wood combustion.) Finally, in regards to cordwood, there is the additional climate change issue that considerable fossil fuel is consumed in its production, i.e., cutting, splitting and  transporting.

Bottom Line – The comparison of the relative climate change impacts between gas fireplaces and wood-burning fireplaces is complex with subtleties beyond the scope of this review. With the current state-of-understanding there does not appear to be a clear-cut winner. Claims to the contrary are usually made by those who have not done their homework or have an agenda.

While the residential use of energy certainly has been considered part of the climate change problem, the overwhelming regulatory and policy focus has been on coal power plants, as well as industry and transportation sources. This may change as the impacts of climate change worsen as they are predicted to do. It seems unlikely that regulatory pressure from climate change considerations alone will favor either wood-burning or gas-fueled appliance use in the near future.

2. Indoor Air Emissions

Spillage of air pollutants into the living space from B-vent fireplaces, vented gas inserts or gas log sets installed into existing cordwood fireplaces could conceptually be an issue. Of most concern would be carbon monoxide. Fortunately, pollutant spillage has been largely eliminated by properly installed, modern appliances that have undergone testing and certification.

This is not to say there have not been isolated incidents, but, by and large, they have been mitigated by resolving venting and house pressure issues and it’s unlikely that indoor air pollution concerns will be a significant factor limiting or restricting their future installation in normal household settings. Testing standards and installation procedures are well accepted and documented.

In contrast, indoor air emissions from vent-free units have impacted their acceptance in some areas. By the very nature of vent-free (ventless) appliances, all products of combustion, both incomplete and complete, enter the living space. This includes carbon dioxide (CO2), water vapor, carbon monoxide (CO), volative organic compounds (VOC), particulate material (PM), and various specific chemical compounds often referred to as air toxics that make up in part the VOC and PM.

U.S. Vent-Free Status

The installation of vent-free fireplaces is restricted in some locations due to their venting of air emissions (water, carbon dioxide and traces of pollutants) in the indoor environment.

Notably, these include some carcinogens such as formaldehyde, benzene, and polycylic organic matter (POM). Not only are air pollutants produced from the incomplete combustion of the gas fuel, but also from the partial combustion of possible impurities such as lint, dust and hair in the air supply.

It’s outside the scope here to engage in the debate over vent-free appliances. However, it’s clear that the fact that their emissions enter the air inside of the home, has, rightly or wrongly, negatively impacted their acceptance. It’s unlikely the debate will be resolved anytime soon. The following are some facts offered without agenda that are worth considering in regards to vent-free gas fireplaces.

  • They approach 100 percent efficiency because no heated gas is vented from the home. All the energy produced by combustion is captured. The only thing that detracts from their overall efficiency is the very small amount of fuel that may not be completely combusted. Certainly this is a strong selling point for them.

  • The carbon dioxide levels in homes from their use can reach levels that cause drowsiness. This is a well-known phenomenon in classrooms and meeting rooms due to occupants’ respiration releasing carbon dioxide. Some ventilation is appropriate and needs to be recommended to homeowners or builders.

  • For every million Btu’s of natural gas burned, approximately 84 pounds (about 10 gallons) of water are produced. Similarly, for every million Btu’s of LPG burned, about 192 pounds of water (23 gallons) are produced. Condensed water can be damaging to the structure of a home and can contribute to mold problems. The seriousness of this issue has been the subject of considerable heated debate.

  • To put it into perspective, the space heating demand for an average U.S. home (38.7 million Btus per year) is illustrative. If a vent-free fireplace is used in the average U.S. home as a sole source of heat, there would be 387 gallons of water released inside the home as vapor after one heating season if natural gas were used as the fuel. There would be 890 gallons of water released if LPG were used.

    Clearly, the best application for vent-free appliances is for secondary heat, in homes that have higher air exchange rates (often characteristic of older homes), that are in milder climates and that are in areas with lower relative humidity. Further, natural gas- fueled units would be less of an issue than LPG units. These are all points that should not be lost when evaluating future products and markets and selling these units to consumers.

  • There are trace levels of particles, carbon monoxide, and carcinogenic air toxics released into the indoor air upon combustion. Carcinogens are not considered to have any threshold exposure limit, meaning that any exposure imposes some risk. Similarly, carbon monoxide competes with oxygen when binding with hemoglobin in the blood to transfer oxygen throughout the body. Even though there are CO standards there are no “good” levels of CO.

    While all this seems onerous, it does need to be put into perspective. As illustrated in the following section, air pollutant emission levels from traditional vented wood-burning fireplaces are dramatically higher than gas-fueled fireplaces. Emissions from wood-burning fireplaces enter the outside air from residential chimneys typically only 15 to 35 feet above ground level. The average air exchange rate of a U.S. home is between 1 and 2 – consequently, and not surprisingly, the air pollutants emitted at much higher levels from wood combustion, which are exhausted to the outside air near ground level, do infiltrate the home.

    Because of this, it’s difficult to predict whether wood-burning fireplaces or vent-free gas fireplaces would produce greater indoor air toxic concentrations. It is, however, clear that vent-free gas fireplaces may not be dramatically different than the traditional wood-burning units in regards to their air pollutant impact on indoor air quality.

Comparison of Emissions

Burning Cordwood, Natural Gas and LPG

The dramatic difference in air emissions from a cordwood-burning fireplace as compared to natural gas- or LPG-fueled appliances is exemplified in the results of a test of carbon monoxide (CO) and particulate matter (PM) emissions from a wood-burning fireplace burning oak cordwood with the same unit retrofitted with an LPG-fueled gas log set and a natural gas-fueled gas log set. Graph shows the mass of particles and carbon monoxide in grams emitted per typical fire.

3. Pollutants Emitted to the Outdoor Air

Restrictions on the use of wood-burning fireplaces will encourage consumers to choose gas-fueled appliances. Use of wood-burning fireplaces as well as uncertified wood stoves and inserts are prohibited during burn bans in the Tacoma-Pierce County Smoke Reduction Zone. Wood-burning during a ban may result in fines of up to $1,000.

There are always winners and losers. Air pollutant emissions for all the traditional pollutants from wood-burning fireplaces have been documented as being much, much higher than from gas-burning fireplaces. For this reason, many air quality jurisdictions have banned the installation of new wood-burning fireplaces or have, through periodic burn bans, restricted their use. These bans will most certainly promote the sale of new gas-burning appliances as well as gas log sets and inserts for retrofitting into existing wood-burning fireplaces.

Notable agencies that have instituted bans or restricted the use of wood-burning fireplaces include: Washington State Department of Ecology, various Washington State local air pollution control agencies, Maricopa County (Arizona) Air Quality Department, South Coast Air Quality Management District, San Joaquin Air Pollution Control District, and Bay Area Air Quality Management District. It’s likely others will follow suit, producing focused geographically-distinct markets for gas appliances.

Part two of this three part series on gas-fueled appliances in the residential hearths of North America will focus on socio-demographics, regionalism, and consumer attitudes.

About the Author

Dr. James E. Houck is a staff writer for Hearth & Home magazine, an adjunct faculty at the University of Portland, and an independent technical consultant specializing in product development, litigation support, environmental impact, energy conservation, and strategic marketing. He can be reached via email.


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