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Manage My Life

How do gas fireplaces work?

by Manage My Life Last activity date:
April 26th, 2007

How do gas fireplaces work?

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Building Supplies
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Manage My Life
Although these are typically decorative appliances, some

gas fireplaces

do provide heat for rooms. Fireplaces with

heat circulators

and

direct vent fireplaces

are more likely to be heating appliances. They may be rated as

space heaters

as a result. The heat circulators can be convection or fan forced. The burner systems can be pilot or electronic ignition systems.

Gas fireplaces and gas logs may be installed in wood burning fireplaces. However, gas fireplaces have more in common with gas furnaces and space heaters than with wood burning fireplaces. Gas fireplaces designed to fit into masonry fireplaces are often referred to as

fireplace inserts

.

Some systems have glass doors which cannot be opened. Others have glass doors which can be kept open or closed.

As with all gas appliances, you should be looking for a label that suggests that the system has been tested by a recognized agency.

Combustion air for these devices may be taken from house air or from outside.

Combustible clearances are typically smaller than for wood-burning fireplaces and are determined by the manufacturer's instructions on the label of the units. Combustible clearances around the openings of fireplaces can often be smaller than the six inches required for wood burning fireplaces.

Generally speaking, gas fireplaces are not permitted in bathrooms unless they are direct venting systems. In some jurisdictions, gas fireplaces are not permitted in bedrooms or bed/sitting rooms unless they are direct vent systems or specifically approved for bedroom use.

Gas fireplaces and gas logs must be vented either through a chimney or through a direct vent system.

Where gas logs are installed in an existing fireplace, the fireplace damper must be permanently opened or removed so that the exhaust can go up the chimney. Gas logs must be rated for use in a masonry fireplace. The fireplace itself must be a noncombustible unit properly designed for burning wood.

Gas fireplaces and gas logs can either have electronic ignition or continuous pilots.

Remote controls are available to turn the fireplace on and off and to control circulating fans. Fans may be manual or thermostatically controlled.

These systems can be vented through a conventional B vent, or can be direct vent systems with special venting. Single-wall metal liners in masonry chimneys are also allowed in some areas. Some systems with B vents have an

automatic vent damper

, similar to the efficiency upgrades on gas furnaces. These vent dampers automatically open when the fireplace comes on and close when the fireplace is shut off. Some systems are

power vented

. The power vented systems can be sidewall vented.

Direct vent systems have an integral outside air intake. Those with conventional venting systems may also have outside air provision. This is an option on some systems.

Combustible clearance requirements for vents vary with manufacturer. In many cases, the required clearance is one inch or less.

Most central furnaces that are direct vent systems use an induced draft fan to remove exhaust products from the home. Many direct vent gas fireplaces rely simply on convection. There is no fan to induce exhaust gases to leave the building. Similarly, there is no fan to draw combustion air in. This all takes place on a convective basis.

Some gas fireplaces contain a heat exchanger to help transfer heat into the house air. Heat is transferred into the house by a combination of radiation and convection. Gas fireplaces that act as room heaters claim efficiencies of 75% or even higher.

A gas fireplace might require a one inch combustible clearance behind it, 6 inches at the sides, 36 inches out in front and 36 inches above. Atypical clearance to a 6 inch wide mantel shelf above the fireplace is 4 inches. Watch for evidence of overheating above the firebox.

Gas fireplaces often have input rates of 5,000 to 30,000 BTUs. Outputs are typically 75% of this.
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by Manage My Life
April 26th, 2007
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