A fireplace may take the chill out of those first frosty days of autumn in cold weather climates, but it may not really be effective in reducing your overall energy bill.

A properly functioning fireplace flue will not only draw out smoke but also about 20 percent of the heated air in the room each hour. Moreover, you are most likely only receiving 15 percent of potential heat produced by each burning log because much of the combustible material in the wood is lost as gas without burning or producing heat. A well-maintained system will last longer, operate more efficiently and save you money. The potential for carbon monoxide exposure is possible if home heating equipment isn't properly tested, serviced and maintained.

This doesn't mean you should give up your dream of cozy nights by the fire. A few simple modifications can increase the energy efficiency of your fireplace.

A heating grate made of hollow tubing that wraps around logs and extends over their tops, can re-circulate heat produced by the fireplace into the room. Certain models are equipped with electric blowers that direct hot air into the room instead of up the chimney.

Fireplace covers also increase heating efficiency. Steel covers with fire-resistant glass enable you to watch the fire while receiving radiant heat through the glass. But be sure to leave your damper open when the fire is burning or the coals are still glowing.

A cover should be placed over the opening of the fireplace at the end of the evening when the fire is nearly extinguished, but hot enough to require an open damper to release smoke. Make certain the cover is tight-fitting around the edges so that room heat does not escape.

New technology can improve the efficiency of an existing open fireplace. Open fireplaces exhaust large quantities of air up the flue, resulting in drafts that pull heat out of the home. Thus, an open fireplace only has an energy efficiency of about 5 to 6 percent. Also, manage your thermostat.　Keep thermostats set at a constant, comfortable level. You can save about　two percent　on your heating bill for every degree you lower your thermostat.

Homeowners can boost the efficiency of an existing open fireplace by installing a gas-fueled or wood-burning fireplace insert. Inserts fill the existing fireplace opening and connect to the existing flue. These inserts, which use a catalytic combustion system, ensure clean burning and provide a 78-percent efficiency. A fan provides natural convection heating and a thermostat ensures steady, even heat.

The type of wood burned also can affect fireplace efficiency. Harder woods such as birch, oak and maple burn more slowly and give more evenly distributed heat. Softer woods such as pine burn faster and more unevenly. Beware of green, unseasoned wood that is difficult to burn and produces a great deal of smoke.

The damper should be kept closed whenever the fireplace is not in use, unless you are using natural ventilation to cool your home. Otherwise, you may find that it could pull expensive heated or cooled air from your house, which adds to your energy bill. To be sure the damper closes tightly, hold a hand mirror inside the chimney base to check for light leaks. As a safety precaution, it's also a good idea to have your chimney swept each year to remove debris and to check for obstructions.

Installing a fireplace also adds to the value of your home. According to statistics compiled by Remodeling Magazine, a fireplace can return as much as 140 percent of the homeowner's investment.