WOOD HEATING

GOAL:

To become aware of the difficulties involved with the operation of wood burning stoves and fireplaces.

OBJECTIVES:

The student will be able to:

1. Identify important facts about a wood burning stove.

2. Name ways to make a wood burning fireplace more energy efficient.

LESSON/INFORMATION:

STOVES

Trees store energy from the sun. Some scientists estimate that there is enough fuel wood available in the nation to heat more than half the homes each year. Trees grow quickly and can easily be replanted. Until recently, if you wanted to use a wood burning stove, you probably used an antique. The fact is, there are many manufacturers of wood stoves today. Some boast of high quality, lifetime guarantees, and many are energy efficient. However, many of these stoves have poor safety features. Careful evaluation is warranted before buying wood stoves/heaters.

Heating with wood has problems other than stove construction. The wood has to be well seasoned hardwood. Burning unseasoned hardwood produces high levels of creosote in the now popular "airtight" stoves. The "older" antique stoves did not have this problem as they burned wood quickly with hot fires, thus consuming most of the volatile chemicals which produce creosote.

HINTS ON WOOD STOVES:

1. Choose a stove with a flat top where a pot of water can simmer during the day. This adds needed humidity into a room.

2. The logs used in most cast iron stoves last much longer than those burned in a fireplace and fewer logs are required to maintain comfortable heat.

3. The wood stove will be most efficient when installed near the center of the house on the first floor.

4. If the stove is heated too hot or too quickly, the top of the stove may warp.

5. A brick wall behind your stove will make it safer to operate and will also hold and radiate heat.

6. With the use of an insulated, double wall stove pipe, there will be less moisture condensation and less flammable carbons and tar build up.

7. A heat exchange for the stove flowpipe is available to increase the heat output.

MASONRY FIREPLACES

At best, a traditional masonry fireplace is a poor heater. The energy efficiency level fluctuates during operation, but is generally much lower than other heaters. 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). Once the fire starts to die down, the efficiency drops to 10 percent or less. While the fire is burning, air is drawn from other rooms and used for combustion of the fire. The rising combustion gases serve as an air pump, drawing additional conditioned air into the fireplace and up the chimney. It then escapes out the chimney, causing unconditioned outside air to be drawn into the home. Due to the extra ceiling penetrations of the chimney or flue itself, fireplaces are a major, year-round source of air infiltration.

If wood heating is desired, an air tight wood stove is a far better heater than a conventional fireplace. Also better than a conventional fireplace is a heat recirculating fireplace which draws room air in through a heat exchanger and returns it to the room.

If a conventional masonry or factory built fireplace unit is used, one should provide tight fitting, high temperature glass doors for the fireplace and a combustion air inlet from the outdoors. Utilizing this arrangement, warm inside air won't be lost and the glass will reradiate the fire's heat and provide warmth to the room occupants. Use nonflammable spray foam and caulk to seal around the chimney penetration at the ceiling and around air intake areas. To minimize flue cavity air leakage: (a) use a triple walled flue and a firestop insulated with unfaced mineral insulation, or (b) if a double walled flue is used for a fireplace cavity in contact with an exposed inside wall, separate the fireplace and flue from the conditioned space by an insulated partition wall which is sealed against air infiltration. Choose damper doors that seal tightly. Seal joints between the masonry and other house materials when the fireplace is on an outside wall.

FACTORY BUILT FIREPLACES

Most fireplaces built today are heat circulating fireplaces. They use a prefabricated steel box covered with brick to give it the look of a masonry fireplace. Many units have builtin ducts that draw air off the floor and through the wall of the units where it collects heat, which rises and exits at the top near the ceiling.

The firebox is low and deep and poorly designed to heat by radiation, so nearly all its heat is convective heat. The steel walls of a prefab unit have little mass to hold heat and they are continually being cooled by circulating air. A prefab unit will rust out in time (approximately 25 years).

There are several methods to get more heat out of your fireplace. The air circulating grate holds the wood on curved, hollow steel tubes. Air is heated in the tube. It rises and is convected out of the top. This is one type of heat exchange.

The two level grate is another method. This grate holds logs in a set position to radiate towards the room. A screen and glass enclosure is another worthwhile investment. The screen is a safety device, while the glass allows you to close off the fireplace opening when the fire is being burned out at night.

ACTIVITY 1:

The following list was originally used for a crossword puzzle. See if you can figure out a word that means the same for each.

1. Preventing the entrance or escape of air or gas.

2. Warmth

3. Ability to obtain year after year.

4. Type of stove used to provide heat.

5. The amount of degree of moisture in the air.

6. Recommended material used in wood burning stoves.

7 Residue to burning wood.

8. Hollow, steel tubes used to hold logs for burning.

9. Something old or ancient.

ACTIVITY 2:

Write remedies for the drawbacks on woodburning stoves and fireplaces listed below.

WOOD BURNING STOVES
DRAWBACKS	REMEDIES
Burning unseasoned wood and producing high levels of creosote
Dries up air in the home
Stove is not heating house efficiently
Top of wood grate warped
Can be a fire hazard
Does not put out enough heat
WOOD-BURNING FIREPLACE
DRAWBACKS	REMEDIES
Causes drafts and wastes heat put out by a central heater
Does not put out enough heat
Cool air infiltrates the house through the fireplace

INFORMATION CHECK:

Fill in the blanks using the following words from the word list below:

grate; cast iron; glass doors; brick wall; tar; two level; center;

radiation; cellar hot; infiltration; heat; seal; exchanger; triple;

seasoned; steel; quickly; carbons; moisture condensation

1. Wood stoves should be installed near the _______ of the house or in the _______.

2. You should only burn _______ wood in your wood stove.

3. _______ stoves last much longer and require fewer logs to maintain comfortable heat.

4. To avoid warping the top of the wood stove or the wood grate, don't get the fire too _______ too _______.

5. In order to make the wood stove safer to operate, build a _______ behind it.

6. By using an insulated double wall stove pipe, there will be less _______ _______ and less flammable _______ and _______ buildups.

7. A heat _______ for your stove flowpipe will increase the _______ output.

8. One of the most common ways to improve the efficiency of a fireplace is to install _______ with an airtight _______ .

9. To minimize flue cavity air leakage, use a _______ walled flue.

10. If wood heating is desired, a prefabricated _______ box which circulates heat should be used.

11. The firebox fireplace is low and deep and poorly designed to heat by _______ .

12. One method to get more heat out of your fireplace is to use the air circulating _______ which holds the wood on curved, hollow steel tubes.

13. The _______ _______ grate is another method to get more heat.

14. Fireplaces are a major year round source of air _______ .

TEACHER'S NOTES:

ANSWERS TO ACTIVITY 1:

1. Preventing the entrance or escape of air or gas. = Airtight

2. Warmth = Heat

3. Ability to obtain year after year. = Renewable

4. Type of stove used to provide heat. = Woodburning

5. The amount of degree of moisture in the air. = Humidity

6. Recommended material used in wood burning stoves. = Hardwood

7. Residue to burning wood. = Creosote

8. Hollow, steel tubes used to hold logs for burning. = Grate

9. Something old or ancient. = Antique

ANSWERS TO ACTIVITY 2:

ANSWERS TO INFORMATION CHECK:

1. center, cellar

2. seasoned

3. cast iron

4. hot, quickly

5. brick wall

6. moisture condensation, carbons, tars

7. exchanger

8. glass doors

9. triple

10. steel

11. radiation

12. grate

13. two level

14. infiltration

Comments or questions to: TechAsmt@LA.GOV

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