It has been estimated that 90 percent of the heat generated by a conventional masonry fireplace goes up the chimney. To help make fireplaces more energy efficient, accessory items recover lost heat and return it to the room.
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 of heat every hour. Further, heat transferred through the unit’s double paned glass doors and frame develops an additional 5,000 BTUs each hour. It requires no electricity or gas for operation and is an easy do-it-yourself installation.
Another type of recovery system combines a grate and heat exchanger to re-circulate fireplace heat back into the room. It can be adjusted to fit standard size fireplace openings. These units can also be used with glass enclosures.
| Estimated Wattage Required To Raise Room Temperature One Degree* | |||
| Floor Area Sq. Ft. | Room Conditions | ||
| A | B | C | |
| 50 | 7 | 10 | 36 |
| 100 | 14 | 20 | 69 |
| 150 | 22 | 30 | 103 |
| 200 | 29 | 40 | 138 |
| 250 | 36 | 50 | 172 |
| 300 | 43 | 60 | 204 |
| 350 | 50 | 70 | 241 |
| 400 | 57 | 80 | 275 |
| 450 | 65 | 90 | 310 |
| 500 | 72 | 100 | 344 |
| ROOM CONDITIONS (based on 8 ft. ceiling) | |||
| (A) Interior Room-little or no outside exposure. | |||
| (B) Room with average door and window area-well insulated. | |||
| (C) Isolated Rooms-cabins, watch houses-no insulation. | |||
| *Because of varying climate, building and insulation conditions, this chart is intended only as a guide to heating requirements. | |||
TUBE GRATES
Tube grates are made of a series of U-shaped tubes fastened together; they replace conventional grates and andirons. 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. It should keep the room air from being drawn up the chimney and, when combined with glass doors, the tube grate can be quite effective.
HEAT EXTRACTORS
Heat extractors are made for both fireplaces and wood-burning stoves, and both kinds operate on much the same principle. Their purpose is to extract additional heat from flue gases beyond what would normally come from the stovepipe or chimney.
Some 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 an existing fireplace may 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 effectiveness of the draft. Since this could cause smoking in a fireplace, it would be wise to put a good heat extractor on a chimney with more capacity than is necessary for the size of the fireplace.
The fact that heat extractors cool the flue gases may cause them to work against the efficiency of a good wood-burning stove. As the flue gases cool, combustion is reduced and the stove itself gives off less heat.
Ease of cleaning a heat extractor is another factor. It collects deposits from wood smoke which affect the unit’s efficiency. Some extractors have a removable plate that allows easy access for cleaning the tubes; others require partial disassembly, which can be inconvenient and messy.
FIREPLACE INSERTS
Fireplace inserts are airtight fireboxes that can be inserted into existing fireplaces to provide some of the advantages 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 specified for use with individual manufacturer models. Manufacturer literature should be checked for correct use.
Gas fireplace inserts are similar to un-vented gas heaters. They can be used in masonry fireplaces as infrared burners to radiate heat. Quality features include oxygen depletion sensor and flame-failure gas shutoff.
GLASS ENCLOSURES
Glass enclosures also help improve fireplace performance. They control air intake, which makes the wood burn more slowly and retains more heat in the firebox; at the same time, the fireplace pulls less warm air from the house.
Glass enclosures can also mean the fire can be left unattended. With doors shut, the fire safely extinguishes itself. The glass doors also permit a full, clear view of the fire while they keep 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, which fit most standard size fireplaces, mount securely against the face of the fire place, overlapping the opening. In many cases, the enclosure comes fully assembled so the homeowner can install it in minutes.
Other features available on some models include:
- Safety locks to ensure that the doors will not open accidentally from the impact of a falling log or gusty downdraft.
- Removable doors for easy cleaning.
- Permanently attached curtain screen.
- Outside side-pull handles to eliminate reaching into the heat of the fire to close the doors.
- Special insert to adapt the enclosure to an arched fireplace.
- Base risers to elevate the enclosure to fit nonstandard fireplaces.
Check your state and local codes before starting any project. Follow all safety precautions. Information in this document has been furnished by the North American Retail Hardware Association (NRHA) and associated contributors. Every effort has been made to ensure accuracy and safety. Neither NRHA, any contributor nor the retailer can be held responsible for damages or injuries resulting from the use of the information in this document.
