Natural Gas Fireplace Efficiency
It seems that every winter the debate arises over whether or not it is a good idea to use gas fireplaces for residential heating. Gas fireplaces account for 10% of all U.S. residential natural gas consumption. Among residential natural gas end-uses, fireplaces rank lower than gas furnaces and water heaters but well-ahead cooking and clothes drying. With so much natural gas consumed by fireplaces, the obvious question is whether it is an efficient means of heating your house. The answer is an emphatic “it depends.”
First, remove unvented gas fireplaces from consideration. These systems burn at higher temperatures and exhaust the combustion byproducts into your living space. They are extremely efficient in that all heat generated is retained in the living space but there is also a risk of oxygen depletion for the inhabitants. Even with safety improvements, these systems are illegal in California and other jurisdictions may ban them through code restrictions. You should never trade efficiency for safety.
Vented systems, however, exhaust combustion gases from the living space through a chimney or flue. There are two main types of vent configurations. A single-pipe system uses heated air from the living space for combustion. This is terribly inefficient as you lose this heated air out the chimney. A two-pipe vented gas fireplace is far more efficient because it uses outside air for combustion and reduces the loss of heated air.
Now that we have settled on a two-vented gas fireplace, the type of firebox deserves consideration. If the gas burners are installed in a traditional masonry fireplace, the only heat that will be produced will be radiant heat. Radiant heat alone does not give you much return on your energy dollar. A metal fireplace insert is a far more efficient configuration. In this scenario, cool air from the living space is drawn into a vent below the firebox, circulates around the firebox, and then re-enters the living space as warm air. This convective heating combined with radiant heating gives you a far greater return on your energy dollar. Some fireplaces even have fans to augment this natural convection and blow the warmed air back into the room.
Given that you have a two-pipe vented gas fireplace insert, does it still make sense to operate the fireplace on a cold winter’s night? Several factors figure into answering this question. You need to consider the cost and availability of alternative heating sources. Gas fireplaces are space heaters rather than whole-home heaters. The benefit of space heaters is that they provide heat when and where you need it. It can be very costly to raise the temperature of the entire home by a few degrees when you only desire additional heat in a single room. Factors such as ductwork losses in central heating systems make the exact calculations difficult. However, it is intuitive that efficient space heating, when used to supplement central heating, can be a reasonable approach.
Next, you have to decide between using the gas fireplace for space heating and using a portable electric heater. While the electric space heater has a distinct advantage in portability, the gas fireplace is typically more energy efficient and natural gas rates are often lower than electric rates on a Btu basis.
Fireplace Usage Tips
Keep these guidelines in mind when using a gas fireplace as home heating appliance:
- Make sure you have a two-pipe vented insert that provide radiant as well as convective heat
- Remember that gas fireplaces should be treated as space heating – they provide little heating benefit outside of the immediate area or room
- Keep the fireplace damper closed unless a fire is burning
- Install tempered glass doors and a heat exchange system that delivers warm air back into the living space
- Have a professional check out the flue damper seal to make sure it fits tightly and has not been warped out-of-shape by heat
- Install a carbon monoxide alarm
The bottom line is that nobody ever gets cozy around a furnace. Gas fireplaces, if properly configured and maintained, provide efficient and aesthetically pleasing space heating. Use them to increase the comfort of a room that you are occupying and avoid bumping up your central heating thermostat.