In recent years, a great deal of effort has gone into making good gas fireplaces. Some excellent units are available that offer a visually attractive flame, are very efficient and can save energy in your home. The key features and terminology you will come across when shopping for a gas fireplace are discussed in the following.
Three basic types of gas fireplaces are widely available in Canada: inserts, factory-built fireplaces (zero-clearance units) and free-standing designs. Your biggest challenge will be sorting through the wide range of models available to select a unit that is as efficient as possible and that suits your particular needs.
Inserts are used to convert existing wood-burning masonry or factory-built metal fireplaces to gas. The gas burner and simulated logs are contained in a special metal housing that fits into the existing fireplace cavity. The unit has a glass front for viewing and a decorative metal trim. Existing chimneys must be relined with an approved vent when a gas insert is installed.
Figure 1 Gas Fireplace Insert in Existing Wood-Burning Fireplace
Zero-clearance gas fireplaces are used in installations where there is no existing fireplace (i.e., during new home construction or as part of a renovation project). The simulated logs and burner are inside their own firebox, around which is an inner and outer shell. This type of gas fireplace can be installed inside the house envelope, even against an outside wall. The manufacturer's instructions must be followed carefully to ensure proper clearances from combustibles and that approved venting materials are used.
Figure 2 Zero-Clearance Direct-Vent Gas Fireplace
Free-standing gas fireplaces typically resemble some of the new wood-burning stoves. These units tend to be more effective in supplying heat to the house, since all of the fireplace's surfaces are exposed to the room.
The glass fronts used on all of these gas fireplaces can be manufactured from tempered or ceramic glass. Ceramic glass is slightly better at transmitting infrared heat into the room. However, its principal benefit is that it can better withstand higher temperatures associated with sealed units.
Figure 3 Free-Standing Gas Fireplace
Venting is required to remove combustion gases from the firebox to the outdoors. Three options are available: natural draft venting, power venting and direct venting.
Many of the gas fireplaces sold today evacuate combustion products using a vertical chimney (gas vent), which takes advantage of the natural draft caused by the temperature of the flame (hot air rises). These units have a draft hood that requires extra house air to isolate the burner from outside pressure fluctuations (see Figures 4 and 5).
Figure 4 Natural Draft Fireplace with Type A Draft Hood
Figure 5 Natural Draft Fireplace with Type B Draft Hood
Natural draft fireplaces typically use a B-vent or, in an existing chimney, an approved metal liner that includes a B-vent or a flexible metal liner.
Some gas fireplaces feature power venting, in which an electrical fan assists the venting process. Power venting allows units to be vented with horizontal and vertical flues from locations in a home where a conventional flue cannot be installed. Although power venting is not yet common, it can improve a fireplace's efficiency and will use less house air, as a draft hood is not usually required.
With a direct-vent fireplace, outdoor combustion air is drawn directly into the firebox through one pipe, while combustion products are exhausted through another. The units are sealed, so there is no room air required for combustion and no loss of heated room air to the outdoors. Direct-vent fireplaces are typically installed on an outside wall, with the vent running directly through the wall, although some models are approved for extended horizontal and vertical flues.
Figure 6 Sidewall Venting of a Direct-Vent Gas Fireplace
Venting may be either coaxial or collinear, as illustrated in Figures 7 and 8. Coaxial venting uses two concentric pipes. The outer pipe brings combustion air in from the outdoors, and the inner pipe exhausts the combustion products. This is the method commonly used for sidewall venting. Collinear venting uses two completely separate pipes: one to supply outside combustion air and the other to exhaust combustion products. This method is most often used where there are space limitations when an existing fireplace and chimney have been retrofitted with a gas insert or where long vent distances and cold temperatures make condensation and vent icing a potential concern.
To be installed in an energy-efficient R-2000* home, a gas fireplace must be either direct-vented (sealed) or power-vented. This provides an additional level of protection against spillage of combustion products and helps increase the appliance's efficiency.
* R-2000 is an official mark of Natural Resources Canada.
Figure 7 Direct-Vent Gas Fireplace with a Vertical Coaxial Vent
Figure 8 Direct-Vent Gas Fireplace with a Vertical Collinear Vent
When purchasing a gas fireplace, ask about its efficiency first. However, a word of caution is necessary: many different methods have been used to measure the efficiency of gas fireplaces, some of which can give misleading results.
Until recently, most efficiency ratings were steady-state measurements – the maximum efficiency the fireplace could achieve operating under controlled laboratory conditions and after running at equilibrium for a long period of time. This measurement does not take into account many of the ways in which heat loss occurs in a fireplace. A steady-state rating is comparable to the good gas mileage a car achieves when cruising on the highway, as opposed to the much lower mileage you get in start-and-stop city driving. With a gas fireplace, the actual operating efficiency of the unit once it is installed in your home will be lower than the steady-state efficiency – in some cases, much lower.
The best way to determine the efficiency of a gas fireplace is to ask for its Fireplace Efficiency rating based on the CSA-P.4 test method. Tests using this Canadian standard for measuring annual fireplace efficiency have shown that some units operated in the 30 percent range, while the better units ranged from 50 percent to 70 percent.
As of September 2003, an agreement between the Government of Canada and the Heating, Refrigeration and Air Conditioning Institute of Canada (HRAI) established an energy efficiency rating system for vented gas fireplaces. The EnerGuide rating system provides consumers with the assurance of a standardized method of testing, allowing them to accurately compare different makes and models. The testing provides a Fireplace Efficiency (FE) rating based on products tested and certified to the Canadian Standards Association (CSA) test standard P.4.1-02.
The standard assesses all gas fireplaces, whether they are decorative units or are used for space heating. It is an accurate measurement that reflects the overall operation of the fireplace, taking into account its use and performance throughout the entire heating season. The FE rating is expressed as a percentage; therefore, the higher the rating, the more efficient the unit. The FE appears on the EnerGuide label and is presented in one of two ways, depending on whether the product literature lists only a single model or multiple models.
The EnerGuide label for gas fireplaces
This EnerGuide label with the vented gas fireplace FE rating is shown on manufacturers' product literature that features a single model. As noted in the rating system explanation in the preceding, the higher the percentage, the more efficient the model.
This label is featured in product literature where multiple models with different FE ratings are shown. Each model number listed in the literature will identify the EnerGuide FE rating directly beside the model number. Note that both labels show the statement “Based on CSA P.4.1-02.” This statement demonstrates that the FE rating is based on the testing method that all gas fireplaces sold in Canada must adhere to.
Energy efficiency considerations
Gas fireplaces are becoming popular, both for new homes and for replacement of units in existing dwellings. Most units are built-in, whereas others are free-standing and resemble a wood stove. If you are looking for a gas fireplace, consider its particular application: Are you looking for a decorative appliance or a heating appliance? Is the unit the right size for the space, or are there supplemental ways to help move the heat to other areas of the home? Do you understand the difference between zone heating and central heating?
Consider these points:
EnerGuide gas fireplaces directory
A directory of gas fireplaces will be made available to Canadian consumers by fall 2004. The directory will enable you to compare the energy performance and operating costs of similar models.
A gas fireplace's input rating is the amount of fuel energy the fireplace can consume in one hour. The output rating is the amount of heat supplied by the fireplace to the house. Both ratings are usually expressed in British thermal units per hour (Btu/h) or in gigajoules per hour (GJ/h).
A high input rating does not guarantee high heat output; heat output depends both on gas input and on the fireplace's efficiency. A high-efficiency fireplace burns much less gas in order to supply the same amount of heat compared with a low-efficiency fireplace. For example, a 20 000 Btu/h fireplace operating at 70 percent efficiency will provide the same amount of heat as a 40 000 Btu/h unit operating at 35 percent efficiency – and it will use only half the fuel in doing so!
Heat output, not input, is the important indicator when determining the proper size of appliance for your needs. Remember that a bigger fireplace is not necessarily better. Take into consideration your home's overall heating demand as well as the area where the fireplace will be installed, and select a unit that will match your needs. In a small room, a fireplace with a high output rating could be overpowering and cause overheating and discomfort, rather than cosiness. It will also consume more fuel than necessary to heat the room. A common problem is oversizing the fireplace for the application. A fireplace with a lower output is the obvious solution. A fireplace that allows you to “dial down” the input considerably through modulation or turndown, or that has some means of moving heat out of the room to other parts of the house, will allow for greater control of heat output to prevent overheating.
In many gas fireplaces, a pilot light ignites the main burner as the unit is turned on. A pilot light is a small gas flame that, on its own, can consume from 600 to 1500 Btu of gas per hour and, if left to run continuously, can significantly increase your annual energy costs. You will save energy and money by turning off the pilot light when the fireplace is not being used, especially during the summer, but also when the fireplace is not in frequent use during the heating season.
Other fireplaces have an automatic starter, such as an electronic ignition or another type of intermittent ignition device, that eliminates the need for a continuous pilot by restarting gas combustion each time a flame is desired. When purchasing a gas fireplace, consider one that does not have a continuous pilot light.
Some homeowners prefer a fireplace with a continuous pilot light because it gives them an auxiliary heat source that is not dependent on electricity (i.e., the fireplace will operate even when there is a power failure). If this is your preference, look for a unit with a simple method for shutting off the pilot and a similarly convenient and safe means of relighting the pilot. Do not confuse this feature with most remote control or wall-mounted switches, which often control the main gas flame while leaving the pilot to run continuously.
Figure 9 Gas Fireplace with Pilot Light
A variable-setting control, which allows you to adjust heat output by regulating the fireplace's rate of gas consumption, is another energy-saving feature to look for when purchasing a gas fireplace. This feature, also known as turndown, enables you to maintain better comfort levels, prevent overheating and still have a flame for viewing. At the same time, you may use less fuel by avoiding much of the energy loss that results when a fireplace repeatedly cycles on and off.
Look for a model that has a wide turndown range. Some gas fireplaces allow you a small turndown to only 70 percent of full load (for a 30 000 Btu/h fireplace, this means being able to reduce gas consumption to 21 000 Btu/h). Other models will allow you to go as low as 20 percent of full load (or down to 6000 Btu/h for a 30 000 Btu/h fireplace).
Some fireplaces can be connected to a certain amount of ductwork (much like a furnace), which can help distribute heat to more remote areas of the home while preventing overheating of the room in which the fireplace is installed.
Many gas fireplaces also offer automatic thermostat controls, which help keep the room temperature at a more constant level by automatically adjusting the firing rate. On efficient fireplaces that have a wide turndown range, this thermostat feature can reduce energy consumption while maintaining comfort and continuous viewing pleasure. However, on units that operate at one setting only or that have a limited turndown capability, the thermostat may end up turning the fireplace on and off frequently, which may affect your enjoyment of the flame and can even waste energy.
An important factor to consider when purchasing a gas fireplace is the unit's heat-exchange capabilities. Gas fireplaces transfer heat to the house by two primary means: radiation and convection.
Radiation is the transfer of heat from flames and hot surfaces to solid objects, such as furniture, walls and people, that are in the direct path of the heat source by means of infrared radiation. The hotter the source and the greater its ability to emit heat, the better the radiant heat transfer. Radiant heat allows people to feel warm, even when the air around them may be cool. In other words, when you can see the flame, you can be comfortably warmed by radiant heat. This capability distinguishes fireplaces from many other heat sources, including central furnaces.
A factor worth considering is fireplace surface area and exposure. The more a unit's surface is exposed to a room, the more readily it gives up heat by radiation and convection. For this reason, free-standing and hearth-mounted fireplaces that protrude from the wall tend to have higher efficiencies.
Figure 10 Convection and Radiant Heat
A well-designed fireplace will have channels around and behind the combustion chamber, through which room air will naturally circulate by convection. This is a process of heat transfer where the cool room air picks up heat energy from the fireplace surface causing air currents that transport heat throughout the room. In addition to relying on convection, some units have a heat exchanger that extracts more heat from the combustion gases and transfers it to the house. Fireplaces that have this feature, known as secondary heat exchange, will usually be more efficient than those that do not.
Variable-speed fireplace fans can increase the amount of convective heat supplied by a fireplace by forcing heat into the room. These fans also improve the circulation of air throughout the room. Look for quiet fans that won't take away from your enjoyment of the fire. A ceiling fan can improve circulation of the heated air from a fireplace and pull the more buoyant hot air down from the ceiling.
Source: Natural Resources Canada (NRCan) - Office of Energy Efficiency