![](https://webarchive.library.unt.edu/eot2008/20090122114907im_/http://www.cdc.gov/nasd/images/line.jpg)
Timothy
G. Prather
University of Tennessee Extension
Using
a wood heater can reduce your heating costs, but many Tennesseans
spend more by heating with wood than if they relied solely
on their primary heating systems. Savings from using a woodburning
heating system depend on installation costs of the wood heating
system and the fuel costs and efficiencies of both the primary
and wood heating systems. This article focuses only on the
fuel costs.
The
type wood and its moisture content are extremely important
factors determining heating value. Dense woods, such as hickory,
red maple and oak, have the highest heating values. Seasoned
firewood, air dried for at least six months while protected
from precipitation, burns easily and efficiently. Freshly
cut firewood contains so much moisture that half the heat
from burning the wood is required to dry it so it can burn.
A fire
in the fireplace is relaxing, but you will be warm on one
side only. Fireplaces deliver ten percent or less of the fire's
heat to the room and will increase your heating bill in two
ways. First, firewood costs more than the value of the delivered
heat. Seasoned oak firewood must cost less than 20 dollars
per cord (a cord is a stack 4 feet wide by 4 feet high by
8 feet long) to provide heat from a fireplace at a cost comparable
to a heat pump. Fireplaces also require a large volume o air
which. The incoming air cools the rest of the house, causing
the primary heater to operate more than if you had no fire.
Airtight
stoves operate at about 50 percent efficiency, and wood furnaces
at about 70 percent efficiency. These can decrease your energy
costs, but the firewood must cost less than about 100 dollars
per cord for the airtight stove, and less than 130 dollars
per cord for the furnace, to provide heat at costs comparable
a heat pump. Green wood must cost less than one-half the figures
shown to be cost effective.
Get
the most from your wood heater by using it to complement your
primary heating system. Learn the strengths and weaknesses
of each system, and operate each for its maximum advantage.
Woodburning
heaters perform best when delivering a moderate to high heat
output. Maintain a moderate fire, with the temperature of
the stovepipe between 300 and 450° Fahrenheit about 18
inches from the stove. This can be achieved by adding small
amounts of wood periodically and regulating the air supply.
Cooler operating temperatures allow excessive creosote buildup,
but 600° Fahrenheit can ignite creosote and cause a chimney
fire. A smoldering fire does not burn wood efficiently, nd
creosote and other products of incomplete combustion clog
the stovepipe and chimney. The interior of a cool stove is
also coated by creosote, insulating the stove and reducing
the heat output.
Conventional
heating systems operate at constant efficiency throughout
the winter, with the exception of heat pumps. Heat pumps are
very efficient when the outside temperature is above freezing,
and efficiency increases as the outside temperature rises.
However, heat pumps must work harder at subfreezing temperatures
because there is less heat available to extract from outside
air. In extremely cold weather, heat pump systems rely on
costly resistance heat.
The
amount of heat your system must deliver is directly proportional
to the difference between the indoor and outdoor temperatures.
With the thermostat set on 68 degrees, your house requires
twice as much heat when the outside temperature is 28°
as when the temperature is 48°.
Each
2° you raise the thermostat setting above 68° will
increase your heating requirement by 10 percent when the temperature
is 48° outside. If the outdoor temperature is 28°,
each 2° thermostat setting increase will increase your
heating requirement by 5 percent. Combined with the increased
heat requirements of colder weather, increased thermostat
settings can become very costly.
What
does all this mean? When the weather is mild, consider operating
only the primary heating system because you need little heat.
Wood heaters arc difficult to regulate for comfort in mild
weather and the smoldering fire produces excessive creosote.
Use the wood heater in colder weather, maintaining a moderate
heat output for efficient combustion. However, use a fireplace
only in mild weather so it will not cool the rest of the house.
![](https://webarchive.library.unt.edu/eot2008/20090122114907im_/http://www.cdc.gov/nasd/images/line.jpg)
Disclaimer
and Reproduction Information: Information in NASD does not represent
NIOSH policy. Information included in NASD appears by permission
of the author and/or copyright holder. More
NASD Review: 04/2002
This
news release was distributed by the University of Tennessee
Agricultural Extension Service, Knoxville, Tennessee 37901.
Publication date: September 1993.
Timothy
G. Prather, Agricultural Safety Specialist, Agricultural Engineering
Department, University of Tennessee Agricultural Extension
Service, Knoxville, Tennessee 37901.
|