Flue Sealers

Even brand-new dampers may not close tightly. Dampers can become warped after the first hot fire. They may even be installed incorrectly to begin with. There are products commercially available to temporarily seal off the flue and stop air from escaping up the chimney. One product is an inflatable stopper that you insert into the flue. Most models are made of heavy plastic with an attached tube for inflating the device. The tube hangs down into the fireplace to remind you that the stopper is there. The flue must be totally cool before installing the stopper.

Most manufacturers recommend cleaning the flue before inserting the stopper to ensure a tight and effective seal. This also minimizes the amount of soot that will fall out of the flue when you remove the stopper. Stoppers cost $50. Depending on how often you use them and your climate, they may pay for themselves within a few years. A less expensive solution is to use an old foam rubber seat cushion or pillow: place it in a heavy plastic bag, and insert this into the flue. Attach a long red tail to it to remind you that it is there.

Chimneys harness the heat of the fire to create what's called a stack effect. As the warm air from the fire rises, cooler house air rushes into the wood-burning appliance through vents, providing the oxygen the fire needs to burn. Starting a fire with a good hot burn will encourage this healthy draft to flow. Also, between the higher and lower pressure zones of the home lies a neutral pressure zone. The neutral pressure zone tends to move toward the largest air leak. When the top of the chimney is located above the home ceiling (as it should be), the chimney's neutral pressure zone is above the neutral pressure zone of the house. This creates a flow of air into the appliance and out the chimney even when no fire burns.

Fireplace Accessories and Inserts

Although wood-burning fireplaces have aesthetic appeal, they may actually remove more heat from a house than they produce. A typical, vertical-back fireplace with an open front is at best ten percent efficient in converting wood to energy and delivering it to a room. The rest of your wood dollars escape up the chimney. They also pull cold air into the house from small gaps around windows and doors. At the beginning and end of the burn, these convective heat losses are larger than the radiant heat provided by the fire. Also, most fireplaces are inappropriately situated on exterior walls. The large mass of masonry that makes up most fireplaces are poor thermal insulators and readily conduct room heat to the outdoors in cold weather.

Rising energy costs are causing more people to look for alternatives and less expensive ways of maintaining comfort in their homes. One of the most logical choices for home heating is wood. It's an easily obtainable renewable resource. If you cut your own wood, it's not as expensive as operating a mechanical heating system run by electricity, natural gas, or coal.

Fireplaces are experiencing a comeback in new home construction and home renovations. A fireplace often adds to the real estate value of a home, making it more attractive. A warm fireplace is so inviting on a cold winter evening, but the benefit of having one stops there.

The truth is, fireplaces are tremendous energy wasters.  

Inefficiency of Fireplaces

At best, a traditional masonry fireplace is a poor heater. The energy efficiency level fluctuates during operation. While the fire is maintained at a high temperature, maximum efficiency will range between 20 and 30 percent (with an indoor/outdoor temperature difference of 40 degrees and moderate winds). But once the fire starts to die down, the efficiency drops to 10 percent or less. That means of all the heat produced by a fire during that cool-down time, only about 10 percent actually helps to heat the room. The rest goes up the chimney. That's quite an expensive way to heat your home, considering that a cord of wood may cost $150. Depending on how large a fire you build and how long it burns, it's possible that a substantial part of your investment goes up the chimney in smoke.

A traditional masonry fireplace is an energy loser because of its basic design. It incorporates a flue and a chimney which create a natural draft of air to prevent smoke and toxic gases from entering the house. The draft also pulls air (oxygen) from the room to support combustion.

Existing heat in the house is pulled right up the chimney, too.

You could be losing more heat than you think.

If a mechanical heating unit such as a gas or electric heater is operating, energy loss will be even greater.

In fact, energy loss through a fireplace happens year round if special measures are not taken to prevent it. Even with the damper closed, air infiltration still takes place. Heat loss occurs up the chimney even when the fireplace is not being used. In summer, cooled air escapes through the closed, but not airtight, damper.

Glass doors will not eliminate air being pulled from inside the home.

Fireplaces

When you cozy up next to a crackling fire on a cold winter day, you probably don't realize that your fireplace is one of the most inefficient heat sources you can possibly use. It literally sends your energy dollars right up the chimney along with volumes of warm air. A roaring fire can exhaust as much as 24,000 cubic feet of air per hour to the outside, which must be replaced by cold air coming into the house from the outside. Your heating system must warm up this air, which is then exhausted through your chimney. If you use your conventional fireplace while your central heating system is on, these tips can help reduce energy losses.

Fireplace Tips

If you never use your fireplace, put a plug in the chimney flue. Keep your fireplace damper closed unless a fire is going. Keeping the damper open is like keeping a 48-inch window wide open during the winter; it allows warm air to go right up the chimney. When you use the fireplace, reduce heat loss by opening dampers in the bottom of the firebox (if provided) or open the nearest window slightly-approximately 1 inch-and close doors leading into the room. Lower the thermostat setting to between 50 F and 55 F. Install tempered glass doors and a heat-air exchange system that blows warmed air back into the room. Check the seal on the flue damper and make it as snug as possible. Add caulking around the fireplace hearth. Use grates made of C-shaped metal tubes to draw cool room air into the fireplace and circulate warm air back into the room.

For more information on heating and cooling, contact:

The Department of Energy's Energy Efficiency and Renewable Energy Clearinghouse (EREC), (800) DOE-EREC (363-3732), www.eren.doe.gov

The Department of Energy's ENERGY STAR web site: www.energystar.gov

The U.S. Environmental Protection Agency at (888) STAR-YES, www.epa.gov/energystar.html

Owens Corning Customer Service Hotline, (800) GET-PINK, www.owens-corning.com/owens

The Air Conditioning and Refrigeration Institute, Fax (703) 528-3816, E-mail ari@dgsys.com www.ari.org

20% of energy loss is due to poorly fitted fireplace flue dampers. The air rushing up the chimney must be replaced by outside air which must be heated up to room temperature, at a considerable energy loss.