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Hearth & Home November 2014

FV41 MOD from Mendota Hearth Products.

Gas: Heart of the Hearth Part III

By James E. Houck

This is the third of a three-part series on gas-fueled appliances in the residential hearths of North America. It focuses on the history of gas in the hearth, the market size and character of the various categories of gas hearth appliances.

The history of gas in America and its eventual use in hearth appliances parallels the American experience. Natural gas was observed in America in 1626, when French explorers discovered Native Americans igniting gases that were seeping into and around Lake Erie.

In 1821, William Hart dug the first successful natural gas well in the U.S. in Fredonia, New York. In 1836, the City of Philadelphia created the first municipally owned natural gas distribution company.

The start of the natural gas industry in the United States. Colonel Edwin Drake’s gas/oil well 1859.

In 1859, Colonel Edwin Drake drilled a well in Pennsylvania that struck natural gas. A 51/2-mile-long pipeline was constructed, running from the well to the town of Titusville. Many consider this first gas transportation pipeline to be the start of the natural gas industry in the U.S.

While natural gas was first used in North America in the mid-1800s, it was the extensive pipeline installation in the early and mid-part of the 20th century that led to the dramatic expansion of its residential usage. The energy crisis of the 1970s also expanded its role.

Liquefied petroleum gas (LPG) was used in the late 19th century but its widespread usage began in the 1940s, primarily in rural areas where the natural gas system did not extend.

The residential use of gas for hearth appliances in particular began in the early part of the 1900s, but it became much more prevalent in the 1950s with improved log and flame appearances. There was a very large increase in the use of gas for hearth appliances beginning in the 1990s, commensurate with realistic flame technology, improved venting systems, improved efficiencies, and lifestyle choices that favored the convenience of gas. More recently, air quality concerns and regulations also have tended to favor gas over cordwood fuel for hearth appliances.

The Place of Gas Among Hearth Fuels

Natural gas- and LPG-fueled fireplaces, inserts and stoves have competition. Everyone in the hearth industry knows there are solid-fuel fireplaces that burn cordwood and wax/fiber firelogs; that there are ethanol (both liquid and gel) fueled fireplaces, and that there are electric fireplaces.

The variety of fireplace insert fuels is even greater than the variety for fireplaces. Besides natural gas and LPG fireplace inserts, there are wood-fueled inserts (burning both cordwood and manufactured firelogs), pellet inserts, electric inserts, coal inserts, ethanol (again both liquid and gel) inserts, and even corn fireplace inserts.

However, among all these fuel types, gas, cordwood, and electric are the big three for fireplaces; and gas, cordwood and pellets are the big three for fireplaces, inserts and stoves.

The relative ranking of the popularity of fireplaces, fireplace inserts, and stoves by fuel type can best be illustrated by looking at the average percent of those appliances shipped in the U.S. annually by manufacturers in the last five years (2009-2013). For fireplaces, ignoring electric fireplaces, the numbers are: 76 percent gas, 24 percent cordwood. Even these percentages do not illustrate the current total importance of fireplaces utilizing gas fuel because, besides gas fireplaces per se, HPBA’s estimate of the average number of gas log sets shipped annually in the last five years is 271,840 units/year.

As noted, the relative ranking of the popularity of fireplace inserts and stoves can also be illustrated by looking at the average annual shipment by manufacturers in the last five years (2009-2013). Again ignoring electric units, for fireplace inserts the numbers are: 48 percent gas, 38 percent cordwood, 13 percent pellet, and 0.5 percent other fuels.  For stoves the numbers are: 16 percent gas, 54 percent cordwood, 27 percent pellet, one percent agricultural fuels, and two percent other fuels.

Percent of Households with Fireplaces by Fuel Type

The Big Three: The overwhelming majority of fireplaces in use are gas, wood or electric. The pie charts illustrate the percentage of households with fireplaces by fuel type among households with a fireplace. Chart on left is from the HPBA’s 2012 “Hearth Consumer Research Survey.” Chart on right is from Natural Resources Canada’s most current identified fireplace tabulations (2007 “Survey of Household Energy Use”).

Electric fireplaces

Electric fireplaces represent a very large fraction of fireplaces sold but are difficult to compare quantitatively with the number of units using the other fuel types for several reasons.

  1. Similar to gas log sets, HPBA can only estimate the number of electric fireplaces shipped because not enough manufacturers choose to report them in HPBA’s manufacturers’ shipment survey.
  2. A large number of electric fireplaces are sold in Big Box stores, by direct mail, or on-line, which is particularly true for lower-end models.
  3. The term “electric fireplace” as commonly used by the hearth industry is not specific and encompasses models that could be considered functionally as fireplace inserts or stoves besides true fireplaces.

HPBA’s estimate of the average number of electric “fireplaces” shipped annually in the last five years is 1.4 million units/year.

Gas log sets retrofitted into solid-fuel fireplaces with conventional chimneys and B-vent gas fireplaces have low efficiencies because hot gases are exhausted from the chimney, with cold outside air infiltrating into the house making up for the loss. Often the room where the fireplace is located feels warm because of the radiant heat emitted directly from the fireplace, while other rooms get colder due to the infiltration of cold outside air.

The Rise of the Gas Fireplace

The percentage of gas fireplaces among fireplace types has been on the rise since the 1990s, mostly supplanting the sale of cordwood fireplaces. According to HPBA’s U.S. manufacturers’ shipment records, the ratio of gas fireplaces to cordwood fireplaces shipped in 1999 was only 1.22 to one as compared to 3.76 to one in 2013.

As math would dictate, because of this increase in the annual sales percentages for gas fireplaces compared to cordwood fireplaces, the percentages of gas fireplaces in use in residences has also been on the rise both in the U.S. and Canada, albeit lagging behind shipment percentages as there are many older cordwood fireplaces still in homes.

It is important to note that the rise in gas fireplace numbers compared to cordwood fireplace numbers is not uniform across the U.S. or Canada. For example, one would expect the number of gas fireplaces to increase less, both in an absolute and a relative sense, in the U.S. Northeast Census Region compared to the West Census Region because fireplaces are less in favor in the Northeast, with a lower percentage of usable fireplaces being reported in households there as compared to the West Census Region.

In addition, a number of states in the Northeast Census Region have a lower percentage of natural gas hookups than states in the West census region, further widening the difference between the two regions.

Geographical differences are even more pronounced for Canada. At one end of the scale, only four percent of Quebec households report having a gas fireplace whereas, on the other end of the scale, 37 percent of British Columbia households report having a gas fireplace (2007 data).

Most certainly, the increase of gas fireplaces compared to cordwood fireplaces has been in part due to the increased availability of gas for residential use, realistic flames, attractive styling of appliances, improved efficiencies, and real and perceived environmental benefits.

However, overlying all these fundamental factors, and perhaps equally or even more important in the choice of gas over cordwood fireplaces, are the pragmatic advantages directly experienced by the consumer. Notably these include:

  1. The convenience of a simple on/off switch and an ever-present fuel supply. (There are no kindling, starter logs or a lingering hot coal bed to worry about, nor is there bulk fuel to purchase, store, age, split and transport.)
  2. A cleanliness factor that is particularly relevant in modern suburban homes, i.e., gas fireplaces generate no mess in terms of ashes, wood chips, bark, etc., and,
  3. The elimination of the inconvenience of periodic chimney cleaning.

Similarly, it is likely that these pragmatic advantages are also responsible for the increased use of electric fireplaces, with only one percent of U.S. households with a fireplace in 2004 reporting that the fireplace was electric in contrast to 14 percent in 2012.

Annual Ratio

Gas to Cordwood Fireplaces that Have Been Manufactured

The annual ratio of gas fireplaces to cordwood fireplaces that have been manufactured has increased by almost a factor of three since 1999. Data from HPBA manufacturers’ shipment records for the U.S. Site-built masonry fireplaces were not part of the analysis.

Annual Ratio

Gas to Cordwood Fireplaces in Residences

Surveys confirm that the ratio of gas fireplaces to wood fireplaces in residences in both Canada and the U.S. has increased significantly since the early 1990s. Data for Canada are from Natural Resources Canada surveys and represent the ratio of households reporting having gas fireplaces to those reporting having wood fireplaces.

Data for the U.S. are from Department of Energy surveys and represent the ratio of households reporting using gas fireplaces as supplemental heating equipment to those reporting using wood fireplaces as supplemental heating equipment.

The Gas Fireplace Insert and Gas Stove Markets

Unlike fireplaces, the percent of gas-fueled fireplace inserts and stoves has not increased dramatically since the late 1990s. The percent of fireplace inserts shipped in 1999 that were gas-fueled was 70 percent (26 percent cordwood and four percent pellet) compared to 54 percent that were gas in 2013 (32 percent cordwood and 12 percent pellet).

The percent of stoves shipped in 1999 that were gas-fueled was 16 percent (59 percent cordwood and 22 percent pellet) compared to 17 percent that were gas in 2013 (52 percent cordwood and 29 percent pellet). The obvious difference between fireplaces, on the one hand, and fireplace inserts and gas stoves, on the other, is that fireplace inserts and gas stoves are more often considered as utilitarian heaters and less often used for aesthetics.

Further, a larger fraction of fireplace inserts and stoves are in households outside the suburbs, in rural areas where there is ready wood fuel availability and a larger fraction of them are in lower income households where lower heating costs offered by cordwood is a factor.

Pellet inserts and stoves have also become more popular, additionally decreasing the fraction of inserts and stoves that are gas. It should, however, be noted that while the percent of gas fireplace inserts has not increased, gas fireplace inserts still represent the majority of the fireplace insert units annually shipped and that, for gas stoves, while fewer are shipped than cordwood or pellet units, they still make up a significant minority of the units shipped and the percentage has not changed much since 1999.

Rating Fireplaces as Essential or Desirable

With experience, homeowners tend to prefer gas fireplaces over cordwood fireplaces. Percentages are of homebuyers who rate fireplaces as essential or desirable. The most reasonable explanation of this trend is that the practical advantages and convenience of a gas over a cordwood fireplace become more recognized and appreciated with actual in-home experience with fireplaces. Data are from a National Association of Home Builders survey of 3,682 recent and prospective home buyers.


In reviewing HPBA’s “Quarterly Industry Surveys,” it’s important to note that data are withheld from some categories when less than three reporting companies are in the category and/or one firm has more than 66 percent of the units shipped.

In reviewing the Natural Resources Canada’s database it’s important to note that:

  1. The efficiency numbers are determined by the CSA P.4 method which are typically several percentage units lower than comparable AFUE determined by DOE 10 CFR Pt. 430, Subpt. B. App O.
  2. The tabulation is for vented zero-clearance gas fireplaces, gas stoves, and vented gas fireplace inserts. Vent-free gas fireplaces, vent-free gas fireplace inserts, vent-free stoves and gas log sets are not included.
  3. The numbers in sub-categories often do not add up precisely to the overall total numbers as some parameters for some models were not reported.
  4. Power venting systems are not separated from the direct-vent and B-vent categories in which the power-vent systems are installed.

The Cold Hard Facts

Most of us involved with gas hearth appliances know the “company lines,” but it’s still good to look at the real facts. To get a cold, hard understanding of the role of various gas-fueled hearth appliances, their characteristics and their importance in terms of commerce, we looked primarily to two large, independently compiled databases. They were the HPBA’s “Quarterly Industry Surveys” and Natural Resources Canada’s tabulation of energy efficiency ratings.

The HPBA’s “Quarterly Industry Surveys” provide the annual number of units manufactured (shipped) and the net sales that they represent1. The Natural Resources Canada’s tabulation of energy efficiency ratings began in September 2003 and required the manufacturers of units sold in Canada to report energy efficiency as determined by the CSA P.4 method.

As many, if not most, gas fireplaces, gas fireplace inserts and gas stoves (referred to as “freestanding gas fireplaces” by Natural Resources Canada) manufactured in North America are on the “list,” the Natural Resources Canada’s tabulation is extensive. It includes 65 different brands and 2,761 models. (3,821models if LPG and natural gas versions of the same models with dual-fuel capabilities are counted separately.)

Besides the brand, model and efficiency, the tabulation also includes the fuel type (natural gas, LPG or both), venting type (direct-vent or B-vent), ignition type (standing pilot, intermittent or on-demand), configuration, i.e., appliance type (zero-clearance gas fireplace, gas stove or fireplace insert), minimum input energy, and maximum input energy2.

Appliance Types – Number of Models

The relative commercial importance of zero-clearance fireplaces, gas stoves and inserts is apparent from the Natural Resources Canada’s database. There have been approximately seven times more zero-clearance fireplace models than fireplace insert models, and nine times more zero-clearance fireplace models than gas stove models.

Maximum Input Ratings for Zero-Clearance Fireplaces

There is a considerable range in maximum input ratings for zero-clearance fireplaces. While the average value for zero-clearance fireplaces tabulated by Natural Resources Canada is 30.6 kBtu/hr, the range extends from a low of 6 kBtu/hr to a high of 103 kBtu/hr (n = 2,953 models, natural gas and LPG versions counted as different models).

Number of Models by Appliance Type
All Models Zero-Clearance Fireplaces Stoves Fireplace Inserts
2,760 2,194 249 316
Maximum Input Energy by Appliance Type
Appliance Type Venting Average Energy Input (Btu/hr) Standard Deviation Around Average* Number of Models Averaged
Zero Clearance Fireplaces or Wall Mounted Direct-Vent 30,375 11,427 2,751
B-Vent 34,530 10,597 100
Vent-Free less than 40,000† ND ND
Stoves Direct-Vent 28,251 6,978 376
B-Vent 32,700 5,904 20
Vent-Free less than 40,000† ND ND
Fireplace Inserts Direct-Vent 30,746 5,940 405
B-Vent 25,929 6,037 55
Vent-Free less than 40,000† ND ND
Gas Log Sets Vented 62,380§ 10,840 88
Vent-Free less than 40,000† ND ND

*A standard deviation is a statistical measure of the spread of data around the mean (average). Plus or minus one standard deviation includes 68 percent of the data points. For example, 68 percent (approximately two-thirds) of zero-clearance fireplaces would have maximum energy inputs between 18,948 Btu/hr and 41,802 Btu/hr. One-third would have maximum energy inputs outside that range.
†Vent-free appliances are limited to 40,000 Btu/hr (10,000 Btu/hr for bedrooms and 6,000 Btu/hr for bathrooms) by the ANSI Z21.11.2 test standard.
§Average and standard deviation were obtained from a non-statistical review of gas log sets offered for sale by 14 key manufacturers as listed on their web pages.
ND = no data

Ignition Types

Concern over efficiency and, correspondingly, the energy consumed by standing pilot lights, has been a topical issue. A typical standing pilot light consumes between about 700 and 1,500 Btu/hour. Standing pilot lights have been widely used over the last 20 years, but there has been movement to use more energy-efficient intermittent and on-demand models.

The Natural Resources Canada’s tabulation shows that nearly half of the total gas appliance models since September 2003 have used standing pilot lights. This suggests that there is a potential and substantial market for retrofitting older standing pilot lights with more modern, more energy- efficient ignition systems.

Number of Models by Ignition Type
Total Number of Models Models with Standing Pilot Lights Models with Intermittent Ignition Models with On-Demand Pilot Lights No Pilot Lights or Data Not Provided
2,761  1,236 1,344 60 121


The average age of a gas fireplace is 12 years compared to the average age of a cordwood fireplace of 21 years (HPBA’s 2012 “Hearth Consumer Research Survey”). This relatively young average age for gas fireplaces is not surprising in light of their rapid rise in sales since the 1990s. With the future aging of the gas fireplace population, it’s reasonable to predict that sales of upgrades, replacement parts and replacement units will become more prevalent at some future time as the number of older fireplaces increases.

Input Energy

Correct appliance sizing is paramount for consumer satisfaction. There are many factors that come into play when selecting a gas appliance with the appropriate heat input. These factors include: room size, climate, home insulation/tightness, the appliance’s efficiency and, for fireplaces, whether it is primarily for decorative or heating use.

Interestingly, while the mid-point of maximum heat input for zero-clearance gas fireplace, gas stove and fireplace insert models appears to be near 30,000 Btu/hour and to be near 60,000 Btu/hour for vented gas log sets, there are many models well above and below the mid-points as illustrated by the large standard deviations around the means for each type of appliance.

This range allows for considerable flexibility in sizing. The larger mid-point for vented gas log sets is, in part, a reflection of their lower efficiencies when installed in masonry or factory-manufactured cordwood fireplaces with conventional chimneys.


Efficiency has become an important parameter for gas appliances used primarily for heating. Everyone wants high efficiency to save money and to save the environment. High and Efficiency used together are buzzwords. Conversely, lower efficiency is desirable for decorative fireplaces because, if too much heat is produced from the required fire appearance, a room may become too warm particularly during milder weather.

Vent-free appliances have the highest efficiencies as none of the heat is vented out of the house. B-vent appliances have the lowest efficiencies as both heated combustion gases and heated excess air are vented out the chimney with cold outside air infiltrating into the house to make up for the loss of the gases going up the chimney.

The efficiencies of direct-vent appliances fall in between. In practice, the in-home efficiencies of gas stoves tend to be higher than zero-clearance fireplaces because much of the heat provided to the room from a zone heater is radiant heat, and a gas stove typically has four sides and a large exposed top from which to radiate heat.

Distribution of Efficiencies for ZC Direct-Vent Fireplaces

The distribution of efficiencies for zero-clearance, direct-vent fireplaces as tabulated by Natural Resources Canada and measured by the CSA P.4 method. The average efficiency is 59.22 percent with a standard deviation of 10.35 (n = 2,605 models, natural gas and LPG versions counted as different models).

Efficiency by Appliance Type
Appliance Type Venting Average Efficiency (%) Standard Deviation Around Average Number of Models Averaged
Zero Clearance Fireplaces or Wall Mounted Direct-Vent 59 10 2,605
B-Vent 21 14 100
Vent-Free near 100* ND ND
Stoves Direct-Vent 66 7 361
B-Vent 57 4 18
Vent-Free near 100* ND ND
Fireplace Inserts Direct-Vent 68 8 393
B-Vent 52 6 55
Vent-Free near 100* ND ND
Gas Log Sets Vented low† ND ND
Vent-Free near 100* ND ND

*Vent-free gas appliances have efficiencies near 100 percent because residential gas appliances typically have combustion efficiencies near 100 percent and no heat is lost out of the home.
†Gas log sets retrofitted into solid-fuel masonry or zero-clearance fireplaces with conventional chimneys lose considerable heat out the chimney. Exacerbating heat loss out the chimney is the fact that existing dampers are usually permanently altered to stay open or are removed with the installation of a gas log set.
ND =no data

Decorative vs. Heater Rated

The distinction between decorative and heater-rated, direct-vent fireplaces has become topical due to the U.S. Department of Energy’s (DOE’s) attempt to require decorative fireplaces to be tested to the same efficiency standards as heater-rated fireplaces. Of course, both decorative and heater-rated gas fireplaces offer a view of flames and simulation of a solid fuel fire, but decorative appliances do not currently undergo efficiency testing nor can they have a thermostat. Heater-rated fireplaces are required to have a minimum thermal efficiency and can use a thermostat.

Further, decorative gas fireplace models often have lower efficiencies so that the desired flame appearance does not produce too much heat for a confined space. HPBA’s “Quarterly Industry Surveys” for 2012 and 2013 separated direct-vent fireplaces into both decorative and heater-rated categories.

In 2012, 57 percent of the 233,620 direct-vent fireplaces manufactured in the U.S. were decorative, which corresponded to $88 million in net sales. In 2013, 67 percent of the 298,873 direct-vent fireplaces manufactured in the U.S. were decorative, which corresponded to $132 million in net sales. The magnitudes of these numbers at risk illustrate the importance of HBPA’s continued struggle with the DOE.

Comparing Contemporary & Traditional Units

Different strokes for different folks. In 2013, 11 percent of gas fireplaces, gas stoves and gas inserts that were shipped (U.S. and Canada) were contemporary and 89 percent were traditional. This corresponds to 20 percent of net dollar sales for contemporary units and 80 percent for traditional units. HPBA data.

Ranking of Gas Appliance Categories
by Net Annual U.S. Sales*
Gas Appliance Category Ranking Net Annual Sales
Direct-Vent Gas Fireplaces 1 (51.8%) $173,215,969
Gas Log Sets† 2 (17.9%) $59,814,000
Direct-Vent Gas Fireplace Inserts 3 (14.4%) $48,260,094
Direct-Vent Gas Stoves 4 (7.2%) $24,056,772
Vent-Free Gas Fireplaces§ 5 (5.3%) $17,588710
B-Vent Gas Fireplaces 6 (2.3%) $7,597,481
Vent-Free Gas Stoves 7 (0.6%) $1,994,430
B-Vent Gas Fireplace Inserts 8 (0.4%) $1,359,189
B-Vent Gas Stoves§ 9 (0.05%) $171,330
Vent-Free Gas Fireplace Inserts 10 (--) --

The Bottom Line

If money equates to importance, the relative importance of each of the gas hearth appliance categories can be assessed from annual net sales. To account for year-to-year variability, annual U.S. net sales were averaged over the last five full years (2009-2103) for the ranking evaluation. Three categories, (1) direct-vent (zero-clearance) gas fireplaces, (2) gas log sets, and (3) direct-vent fireplace inserts, together account for over 84 percent of the total net sales. The direct-vent gas fireplace category was clearly the leader with 51.8 percent of the average annual net sales alone.

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.


Manufacturers Discuss Sales, Products, Trends,
Regulations and the Future of Gas Hearth Products

Hearth & Home recently interviewed a few of the industry’s leading manufacturers to get their perspective on gas hearth appliances, where the market is now and where the products and that market are headed.

Read Heart of the Hearth – Part I


Read Heart of the Hearth – Part II

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