Clemson University Cooperative Extension Service
Home Heating with Wood
To Cope With Inflation
One
of the main causes of today's inflation is the price of energy,
especially the fossil fuels used to heat many homes as well
as to run our vehicles. The interest in alternative energy sources,
mainly wood, to heat the home has grown significantly over the
past years, largely by moderate income families trying to reduce
the bite of inflation but also by a sizeable segment of low
income families who simply cannot afford fossil-derived fuels.
The following compares economic considerations among energy
sources for residential heating. Additional information may
be found in Extension Circular 584, Home Heating with Wood.
Before
you select a wood heating unit, consider these questions:
(1) Is a wood heater already in place and available for use?
(2) Is the heater desired for supplemental heat or as the
sole source of heat? (3) Where is the heat desired-in a localized
area or a large area? (4) Is the heat required throughout
the day or only in the evenings after family members are home?
(5) How high do you want to keep room temperatures? (6) Are
the quantitative factors (efficiency and economics) most important
or are the qualitative factors (aesthetics, desire for radiant
heat, etc.) also important?
If your
house is already built and has a masonry fireplace, consider
using the fireplace as efficiently as possible or add a stove
to use the existing chimney. Depending on the house design
and the desire to heat the entire house, you may need to add
another stove at a different location in the house, add a
wood or combifurnace, or make some structural changes to allow
a central location for a wood stove. If you plan to build
a house with efficient wood heating in mind, make plans to
allow for a central wood stove location so heat can radiate
throughout, or plan for hot air ducting or hot water piping
from a woodfired furnace. The key is to PLAN AHEAD.
Base
your judgments of the heating capacities of wood stoves or
furnaces on experience rather than just the dealer's statements
or manufacturer's claims. Evaluate the heater's capabilities,
and also negative aspects, by seeing it in operation in homes
and talking with others using one. Make sure you compare the
differences in house design and the way it is located and
used in the houses observed. Do they keep the temperature
about like you desire it and, if not, will it fit your needs?
In the
Southeast, most medium to large wood stoves (circulating or
airtight radiant types) can heat 1,000 square feet of living
area to most people's satisfaction and up to 2,000 square
feet for those having the wood stove ideally located and desiring
somewhat lower temperatures. Wood or combination wood and
fossil fuel fired furnaces can be added to heat almost any
house. Ducting hot air or distributing hot water may present
problems if ducts or pipes are not already in place. Remember,
wood stoves that are not airtight or that are inserted in
a fireplace will not provide as much useful heat as an airtight
stove placed where it can radiate or circulate heat in all
directions. However, the fireplace insert performs satisfactorily
for most people and has the advantage of requiring no additional
floor space.
Heat
distribution from wood stoves can be improved in some houses
by operating the fan on the main heating unit, such as a heat
pump, when the wood stove is being used. You may also want
to use a wood stove for cooking and for heating water, especially
when the power is out. Some heating stoves provide a good
cooking surface; others do not.
Circulating
Versus Radiant Stoves:
Some people simply like radiant heat rather than convective
heat as distributed by the circulating stove. However, if
young children are in the family, consider the circulating
stove; its surface temperature is much cooler than that of
the radiant stove and fewer burns would result. When selecting
a stove, also weigh the improved efficiency, and thereby lower
wood requirement, of the airtight stove versus the nonairtight,
which is lower priced. Efficiencies and airflow requirements
are given in Circular 584. Airflow requirements are important
as a certain airflow must be maintained to support adequate
combustion; much lower flow is needed for the more tightly
constructed stoves than the loosely constructed stoves or
fireplaces. Because recently constructed and well maintained
houses are tighter than those built 25 or more years ago,
problems sometimes occur when ventilation air is not adequate
to operate a fireplace or open stove. Refer to Info. Leaflet
No. 9, "Chimney Draft Problems," for ways to solve these problems.
Be sure
to evaluate dealer reliability and services before buying
any type of heater. For many people, heater installation and
service follow up by the dealer is a necessity. If the heater
is not installed correctly, it can be catastrophic. Refer
to Info. Leaflet No. 8, "Wood Stove Installation," for recommendations.
The
following is called the Smithers method for estimating the
number of cords of wood to heat a house. A standard cord is
a well stacked pile of wood 128 cubic feet in volume, a pile
4 feet by 4 feet by 8 feet. Most people have some way to arrive
at the amount of conventional fuel it takes to heat the house
for an average year.
The
Smithers method assumes the following equivalents to one cord
of average dry hardwood* (W):
150 gallon
No. 2 fuel oil
230 gallon LP gas
21,000 cubic feet natural gas
6,158 kwh electricity
*Dry hardwood
is not as commonly sold as green hardwood, which requires about
20 percent more volume to yield equivalent energy to the air dry
hardwood.
Use
the following Energy Efficiency values:
Eb |
Heater |
Ew |
Wood
Heater |
0.65 |
Oil
Furnace |
0.10 |
Fireplace |
0.70 |
Gas
Furnace |
0.25 |
Improved
Fireplace |
1.00 |
Electric |
0.30 |
Nonairtight
Stove |
0.65 |
LP
Gas |
0.50 |
Airtight
Stove |
|
|
0.60 |
Wood
Furnace |
|
|
0.65 |
Airtight
Stove with Catalytic Combustor |
The Smithers
method equation is:
Cords =
| B
x E b
-------------------------
W x E w |
Where
B = units of conventional fuel consumed per year.
Example
1: Assume you are considering purchase of a wood furnace and
your use of No. 2 fuel oil has averaged 500 gallons per year
in recent years. How much wood is needed to produce the same
quantity of heat if a wood furnace is used?
Cords
=
|
500 gal x .65
--------------------------------------
150 gal x .60
| =
3.6 cords |
Example
2: Assume you are considering purchase of an airtight stove
with catalytic combustor and your use of natural gas has averaged
60,000 cubic feet per year in recent years. How much wood
is needed to produce the same quantity of heat if an airtight
stove with catalytic combustor is used?
Cords
=
| 60,000
cu ft x .70
-------------------------------------
21,000 cu ft x .65
| =
3.1 cords |
Before
considering the following examples, refer to Circular 584
for certain definitions, such as cord, efficiency, BTU, and
energy equivalents. Also check for wood characteristics, including
weight and heating value per cord of wood species common to
South Carolina. I. First, let's compare wood with other fuels,
being concerned only with wood that is split and delivered
to the house at a specific price.
A. Cost
per Million Btu's (MBtu) Useful Heat Into the Room:
1) Fuel oil at $1.00 per gallon: There are 140,000 Btus per
gallon of fuel oil and oil furnace efficiency equals 0.65:
1,000,000
Btu x $1.00/gal
-------------------------------------
140,000 Btu/gal x .65
|
= $10.99/MBtu |
Note
1: Fuel oil at any other price is a multiple of this.
For example, with fuel oil at $1.50 per gallon, the cost per
MBtu = ($10.99/MBtu) x 1.5 = $16.48/MBtu since $1.50 per gallon
is 1.5 times the $1.00 per gallon price.
(2) Electricity at $.10/kwh, 3,414 Btu/kwh, and efficiency
equals 1.0:
1,000,000
Btu x $.10/kwh
--------------------------------------
3,414 Btu/kwh x 1.0
|
= $29.29/MBtu |
Note
2: Electricity at any other price is a multiple of this.
For example, with electricity at $.08 per kwh, the cost per
MBtu = ($29.29/MBtu) x 0.8 = $23.43/MBtu since $.08/ kwh is
0.8 of the $.10/kwh price.
(3)
Natural gas at $1.00/100 cu ft, 1000 Btu/cu ft, and efficiency
equals 0.70:
1,000,000
Btu x $1.00/100 cu ft
--------------------------------------
1,000 Btu/cu ft x .70
|
= $14.29/MBtu |
Note
3: Natural gas at any other price is a multiple of this.
For example, with natural gas at $.70 per 100 cu ft, cost
per MBtu = (14.29/MBtu) x 0.7 = $10.00/MBtu since $.70/ 100
cu ft is 0.7 of the $1.00/100 cu ft price.
(4)
Wood (between green and air dry red oak) at $120/ cord, 19.6
MBtu/cord, and efficiency of airtight stove equals 0.50:
1,000,000
Btu x $120/cord
-------------------------------------------
19,600,000 Btu/cord x .50
| =
$12.24 /MB+u |
Note
4: Wood prices will vary considerable across the state.
B.
Fuel Quantity /Cost Comparison:
A homeowner is using 700 gallons fuel oil per year and wants
to switch to wood heat using an airtight stove and half dry
red oak at the above prices. Compare these:
(1)
700 gal fuel oil x 140,000 Btu/gal x .65 efficiency = 63.7
MBtu Annual cost = 700 gal x $1.50/gal = $1,050
(2)
Wood required =
63.7 MBtu useful heat/season
-------------------------------------
19.6 MBtu/cord x .50 eff.
| =
6.5 cords |
Annual
cost = 6.5 cords x $120/cord = $780
(3)
Savings by using wood = $1,050 $780 = $270/ season
(4)
Wood/fuel oil energy equivalence for these conditions: 700
gal fuel oil = 6.5 cords red oak or 1 cord red oak = 108 gallons
fuel oil
C. How
Much Can You Afford to Pay for Wood Compared to Conventional
Fuels When Using an Airtight Stove?
(1)
Cost/MBtu ΒΈ cords wood to give MBtu (useful heat into room)
(2) From A.1 above, fuel oil at $1.50/gal $16.48/MBtu; cords/MBtu
useful heat =
1
MBtu
--------------------------------------
19.6 MBtu/cord x .50 eff.
| =
.102 cord |
16.48/MBtu
-----------------------------------
.102 cord/MBtu
| =
$161.57/cord |
(3)
Electricity at $.08/kwh = $23.43/MBtu
$23.43/MBtu
-------------------------------
.102 cords/MBtu
| =
$229.70/cord |
(4)
Natural gas at $.70/100 cu ft = $10.00/MBtu
$10.00/MBtu
------------------------------
.102 cord/MBtu
| =
$98.04/cord
|
II.
Consider the case where you have your own tools for cutting
wood and you have a pickup truck to haul it. You have located
a good place to cut wood 4 miles from your home at a $25/cord
charge for what is taken. The pickup will haul 1/ 2 cord of
wood when it is well stacked. You figure you can cut, load,
and haul a load in 3 hours and split and stack a load in 2
hours. You plan to cut the season's requirement mentioned
above (6.5 cords).
Let's
figure the annual wood cost:
Permit
Charge: |
$25/cord
x 6.5 cords |
= $162.50 |
Transportation: |
8
miles/trip x 13 trips
35 x $.40/mi. (est.) |
=
41.60 |
Chain
Saw: |
$35
F.C. + $30 O.C. |
= 65.00 |
Other
Tools, |
Personal
Protective Equipment: |
= 25.00 |
Labor
Costs: |
Cut/haul
3 hr x 11 loads x $5/hr |
= 65.00 |
Split/stack |
2
hr x 11 loads x $5/hr |
= 10.00 |
|
Total
= |
$569.10 or
$65.67/cord |
Good
points can be made as to why some of these charges should
be higher or lower than indicated. For example, some people
say they enjoy that type of work and do not feel a labor charge
is necessary; on the other hand, some who perform hard physical
work during the normal work day would say the labor charge
is too low. Also, many people may have wood on their own land
or have free access to wood, eliminating that charge. Cost
comparisons must be tailored to fit each specific case.
III.
Another major economic consideration is that of the fixed
cost for the wood heater as compared to that for the conventional
fuel heater. A simplified comparison is given. Consider the
fixed cost for buying and installing an airtight stove to
be $2,100. The same heating capacity oil furnace could be
purchased and installed for $1,700 at a difference of $400
in investment.
Assume
the lifetime for each of the heaters to be 15 years when maintained
properly. If current interest rates are used and the loss
of this interest on the $400 investment difference is added
to the $400 difference, the annual saving in fuel cost by
using wood would have to exceed about $111 to economically
justify the wood stove over the oil furnace. Reference to
I.B.(3) indicates the annual savings for using wood to be
$270 without considering the investment.
If the
oil furnace initial cost were more or the wood stove were
less, the annual savings by using wood would not have to be
as great. On the other hand, if the difference in investment
costs between the two furnaces were greater than the $400
illustrated, the annual savings would have to be even greater
to economically justify the wood stove.
Current
Fuel Type____________________
Annual
Fuel Usage________________________
Wood
Equivalent to This:
Cords
=
| Annual
fuel quantity x E heater
-----------------------------------------------
One cord wood equivalent x E wood heater
| =
___________________ |
Heat
Producing Appliance Clearances. NFPA No. 89M, National
Fire Protection Association, 470 Atlantic Avenue, Boston, MA
02210.
Chimneys,
Fireplaces, and Vents. NFPA No. 211, National Fire Protection
Association, 470 Atlantic Avenue, Boston, MA 02210.
Heating
With Wood. Larry Gay. Garden Way Publishing, Dept. 90731,
Charlotte, VT 05445, 128 pp.
Planning
and Building Your Fireplace. Margaret and Wilbur F. Eastman,
Jr. Garden Way Publishing, Dept. 90731, Charlotte, VT 05445,
128 pp.
Woodstove
Cookery. Jane Cooper. Garden Way Publishing, Dept. 90731,
Charlotte, VT 05445, 204 pp.
Woodstove
Directory. 1986. Communications Press, P. O. Box 4474,
Manchester, NH 03108.
When
Does It Pay To Burn Wood." 1980. Paul Stegmier and L.
T. Hendricks. Wood Burning Quarterly - Home Energy Digest.
V.4(2):4953.
How
To Buy the RightSize Wood Stove." 1978. Charles Banker.
Wood Burning Quarterly - Home Energy Digest. V.3(1):8188.
How
Many Cords Are Enough." 1978. Michael Harris. Wood Burning
Quarterly - Home Energy Digest. V.2(4):1618.
Disclaimer
and Reproduction Information: Information in NASD does not
represent NIOSH policy. Information included in NASD appears
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NASD Review: 04/2002
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