HEAT RECOVERY SYSTEMS
One type of heat recovery system looks like a glass fireplace enclosure but actually generates heat through convection. A mini-radiator in the hood of the enclosure and a heat exchanger behind and above the fire can generate 10,000 BTUs (British Thermal Units) of heat every hour.
Furthermore, heat transferred through the unit's double-paned glass doors and frame adds another 5,000 BTUs per hour. It is an easy do-it-yourself installation.
Another type of recovery system combines a grate and heat exchanger to recirculate fireplace heat back into the room. It can be adjusted to fit standard-size fireplace openings. These units can be used with glass enclosures.
Tube grates are made of a series of U-shaped tubes fastened together; they replace conventional grates and andirons (metal supports for holding wood in the fireplace). The fire is built on the lower curve of the tube grate, just as it would be built in a standard grate or on andirons.
The purpose of the tube grate is to pull room air into the bottom tube opening, move it around and over the fire--warming the air as it goes--and shoot it back into the room. This is accomplished through gravity or with an electric motor to force the warm air back into the room. The tube grate should keep the room's air from being drawn up the chimney and is quite effective when combined with glass doors.
Heat extractors are made for both fireplaces and wood-burning stoves, and both operate on the same basic principle. Their purpose is to extract additional heat from flue gases beyond what normally comes from the stovepipe or chimney.
Some heat extractors operate naturally using radiation or convection; others have an electric blower to force out more heat.
Since it must be mounted on the stovepipe or chimney, installing a heat extractor on a fireplace can be a major undertaking, unless the fireplace has an exposed chimney.
A heat extractor can pull a tremendous amount of heat from a fireplace chimney, but as it does so, it cools the flue gases and reduces the draft's effectiveness. Since this could cause a fireplace to smoke, it is wise to put a good heat extractor on a chimney with more capacity than is necessary for the size of the fireplace.
Fireplace inserts are airtight fireboxes that can be inserted into fireplaces and mimic some of the effects of a wood-burning stove. Most draw air from the room, circulate it around the insert and return warmed air to the room. Some units have blowers to help distribute the heat.
Some fireplace inserts have a UL listing for use in factory-built fireplaces. These zero-clearance inserts can extend to the fireplace facing. These units are only intended for use with individual manufacturer models. Check manufacturer literature for correct use.
Glass enclosures improve fireplace performance. They control air intake, making the wood burn more slowly and retaining more heat in the firebox; at the same time, the fireplace pulls less warm air from the house.
The fire can be left unattended with glass enclosures. With doors shut, the fire safely burns itself out. The glass doors also allow a clear view of the fire while keeping smoke and sparks out of the room.
Most enclosures have a built-in draft at the base that directs air to the bottom of the fireplace opening so homeowners can easily start and control the fire.
Glass enclosures mount securely against the face of the fireplace and overlap the opening. Usually, the enclosure comes fully assembled and installs in minutes.