Wood vs Natural Gas Cost Comparison
I’ll show you how to work through the calculations for a wood vs natural gas cost comparison to determine if it is cheaper to heat your house with wood or gas. You can follow through with me, or jump to the end to see the results.
We’ll determine the heat that can be realistically recovered from burning a cord of wood, and then determine the equivalent amount of natural gas required to produce the same heat.
First we have to know the efficiency of equipment burning each of the fuels. Wood burning stoves typically vary from 65% to 75%, so I’ll use an efficiency of 70%.
Furnaces that burn natural gas are typically 80% to 97% efficient today. I’ll make the assumption that our furnace is not one of today’s high-efficiency condensing types, which costs more. Non-condensing furnaces are typically 80% to 90% efficient, so we’ll assume our furnace is 85% efficient.
The recoverable heat value of wood varies considerably and depends on the moisture content of the wood as well as the kind of wood. Below are recoverable heat values of various pines based on an average moisture content of 20%. The moisture value can be reached by drying wood for 4 to 6 months prior to burning. The unit is million Btu per cord of wood (mmBtu/cord).
- Jack Pine = 17.1 mmBtu/cord
- Lodgepole Pine = 19.3 mmBtu/cord
- Norway Pine = 17.1 mmBtu/cord
- Yellow Pine = 22 mmBtu/cord
- White Pine = 14.3 mmBtu/cord
- Ponderosa Pine = 15.2 mmBtu/cord
Let’s use an average of 18 mmBtu/cord for the recoverable heat value of our wood. You can find heat values for many other woods here.
Now let’s look into costs. As with the heat content of wood, the cost of a cord of wood can vary considerably, from free to hundreds of dollars. My experience is that is costs somewhere around $150 per cord for cut firewood so I’ll use that cost.
Side note: One cord is a neatly and fairly tight-stacked wood pile measuring 4 feet x 4 feet x 8 feet. That is 128 cubic feet. If you stack wood in a pickup truck with a bed size of 6 feet x 4 feet x 2 feet high, that’s 48 cubic feet. 48 cu.ft. / 128 cu.ft. = .38 cord and .38 cord x $150 = $57. How high wood is stacked in a truck, the size of the bed, how tightly it is stacked, fender wells, etc. can all affect how much wood your truck can hold. Just be careful to avoid getting ripped off when buying wood!
Back to our cost comparison. We have determined that it costs $150 to get 18 mmBtu of heat from wood burned in a wood stove.
Now, let’s determine what natural gas costs – not some number off the charts, but what you and I really pay for it.
Natural gas cost tends to decrease as volume used increases. That is because all the add-ons like taxes, riders, customer charges, consumption charges, etc. become a smaller percentage of the total bill as the quantity of gas used increases. For a residential bill these add-ons are often the majority of the costs on the bill.
As I write this, the natural gas commodity market price has been in a trading range between $3.50 and $4.00 per mmBtu. To convert cost per mmBtu to the cost per thousand cubic feet (mcf) used for most residential bills, multiply $ per mmBtu by 1.023. So $4.00 per mmBtu is equal to $4.09 per mcf. If your bill uses hundred cubic feet (ccf), simply move the decimal one place to the left for the cost, so the price would be $.409 per ccf.
If you only use 2 mcf in a month, assuming a market cost of $4.09/mcf, you might expect your bill to be $8.18 plus some taxes. Well, not exactly – the monthly gas bill for a typical residence is around three times the market cost of gas used. All the add-ons are likely to be more than 200% of the cost of the market price of the gas. I saw a residential bill recently where the monthly usage was 2 mcf and the total cost of the bill was $26.17 – and that is the norm. The gas company must transport the gas from the source to your home, do quality checks, handle billing, maintain the infrastructure, and on and on – so all the added costs are very necessary and legitimate. The takeaway here is that the cost can be deceiving until you look at the details. And keep in mind that this is just an example. Your gas bill will be different depending on where you live, the time of year, current gas markets, etc. And the ratio of fixed costs to natural gas burned will decrease as you burn more gas. Because of all these variables I strongly recommend using your actual bills to determine cost per mcf.
Hint: To keep it simple, take a gas bill for your house for the month you want to compare with wood cost (January for example) and divide the total cost of the bill you paid by the number of mcf burned. That will give you the real cost per mcf for that month.
So let’s be realistic as to the cost of natural gas for heating our homes. 2 mcf being billed at $26.17 is a cost of about $13 per mcf. I’ll use that in comparing wood and natural gas heating costs.
Let’s summarize what we have so far:
Wood – $150/cord and 1 cord = 18 mmBtu
Natural Gas – $13/mcf and 1 mcf = 1.023 mmBtu
These numbers are the actual heat content that can be realized by burning each of the fuels. But the devices used to burn the fuels are not 100% efficient, so we have to derate the mmBtu numbers by the efficiency losses for wood stoves and furnaces.
So for wood stoves, the actual obtainable heat is 18 mmBtu x .70 = 12.6 mmBtu.
And for gas furnaces, the actual obtainable heat is 1.023 mmBtu x .85 = .87 mmBtu.
Now, let’s see how many mmBtu’s of natural gas are equivalent to one cord of wood.
12.6 mmBtu/cord divided by .87 mmBtu/mcf = 14.5 mcf/cord.
And 14.5 mcf/cord x $13/mcf = a natural gas cost of $188.50 for an equivalent cord of wood.
So, based on our assumptions, it costs about $38 more to heat your home with a furnace burning enough natural gas to equal the heat content of 1 cord of wood, as compared with burning 1 cord of wood in a reasonably efficient wood stove.
Keep in mind that 1 cord of wood lasts quite a while and you have to burn a full cord in order to save the $38. For all practical purposes the two fuels cost the same.
Also keep in mind that wood burning pollutes much more than natural gas and requires far more work, namely hauling and stacking the wood, stoking and tending the fire, and cleaning out all the ashes afterward. A furnace gives much more uniform heat in a home and you don’t have to think about smoke and draft issues. It’s hard to beat today’s efficient furnaces burning clean natural gas.
Personally, I would heat with natural gas and use wood stoves for aesthetics and in locations where gas is not available.
I’ve led you through all the details and how the assumptions were made to arrive at this conclusion. You can see how the real costs can easily be twisted by using the market cost of natural gas instead of what we really pay, changing the efficiency of the burning appliances, or assuming a different heat content for the wood being burned. Lots of variables give marketing people room to swing the results any which way they desire. I encourage you to run through the calculations using the numbers unique to your situation. If you have access to free or very low cost firewood, heating with wood becomes a compelling choice.
Wood is a biomass fuel. Learn more about burning wood and other biomass fuels here.
What are your thoughts? Share them below.