How much can you save burning wood?


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

With these figures in mind you can see the savings of burning wood.


If you typically use 1000 gallons of oil a season and with the current price running around $4.40 each.

thats $4,400.00 for oil   and at $250.00 a cord  times 6.5 cord your cost = $1650.00


You can clearly see the difference:


Oil           $4,400.00

Wood     $1,650.00        Saving $2,750.00


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 ¸ 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

.102 cord/MBtu
= $161.57/cord

(3) Electricity at $.08/kwh = $23.43/MBtu

.102 cords/MBtu
= $229.70/cord

(4) Natural gas at $.70/100 cu ft = $10.00/MBtu

.102 cord/MBtu
= $98.04/cord