Installing a Wood Burning Stove is step 5 along the path to complete energy freedom, and I am happy to say it is now complete! There is nothing like the smell of a wood fire. It takes me back to camping trips in Ireland, and across the US in summers gone by, and hopefully summers in the future also. And so when it came to deciding on the first step (after insulating, putting on a jumper and removing as much energy demand as possible) to eating into the large gas bill which accompanies a gas (or worse, carnosine or oil) central heating system, I chose wood.
I am very, very glad to declare that the main source of heat in our house now looks like this:
Knowing every few logs I put on this fire is removing the need to transport cubic metres of gas from Russia and burn it in a boiler, along with paying for the privilege is one of the most satisfying things I’ve done in a very long time.
The Brass Tax
We’ve already looked at many options for heating and cooling a house efficiently. Now let’s look at a wood burning stove in detail. First let’s figure out how much gas costs (use the same method for oil heating, electric heating, etc.) Looking on the internet, I see the gas consumption of our gas boiler (Glowworm Boiler) is 2.3 m^3 of gas per hour at 90% efficiency. Another internet search says that 1M^2 of natural gas contains 11kWh of chemical energy. That means the boiler consumes 2.3 M^3 * 11 kWh per M^3 = 25.3 kWh of gas per hour (outputting 25.3 * .9 = 22.77 kWh at 90% efficiency).
Gas costs €0.06 per kWh on our bill, and finally, the CO2 Emissions of gas are 0.23 kgCO2/kWh.
Now we have all the figures we need. We just need to estimate how many hours / kWh of gas the wood burning stove will avoid the need for. To do this, I’ve made a relative conservative estimate that we will light the stove 3 times a week on average throughout the year (probably most nights in winter and not at all in summer, and about half the time in Spring and Autumn) and each time we light it, it averts about 4 hours of running the gas boiler. That’s 12 hours a week of gas it will prevent us burning in the gas boiler.
Savings resulting from not running gas boiler for 12 hours a week:
® M^3: 12 hours * 2.3 m^3 per hour = 27.6 m^3 of gas per week
® kWh: 12 hours * 25.3 kWh = 303.6 kWh of gas per week
® Money: 303.6 kWh * €0.06 per kWh = €18.22 a week saved or €18.22 * 52 = €947.44 a year ($1000)
® CO2: @0.23 kgCO2/kWh means .23 * 303.6 = 69.828 kgCO2 / week
So yearly, that’s
® €18.22 * 52 = €947.44 a year ($1000).
® 303.6 kWh * 52 = 15,787.2 kWh per year.
® 69.828 * 52 = 3,631.05 kgCO2 / year
Wow – $1000 a year! Saving 15,787.2 kWh of gas and 3.6 tonnes of C02 in the process?
The Payback and 10 year return
The cost of having the stove installed, installing a new, bigger, super-insulated hot water tank and running pipes from the stove in the sitting room, through the walls up to the hotwater tank came to €4000. I estimated a yearly saving of €947.44 above, and it’s actually turned out to be €828.88 a year, so the estimate was pretty good. So:
® Cost: €4000
® Saving: €828.88 per year
® €4000 / €947.44 = the stove pays for itself in 4.22 years
The stove will fully pay for itself in 4.22 years, and then return a profit of €8,288 ($10,000) over the following 10 years.
Wait, aren’t you just replacing one CO2 source (gas) with another one (wood)?
Yes. And that’s the point. Gas represents plants that died a long time ago and who’s carbon is now locked up in the ground. Trees growing now suck carbon out of the air and save that in the bark of their trees. Once the trees aren’t cut down from somewhere they wouldn’t have otherwise been (say, a rainforest), then burning wood results in no net addition of carbon to the atmosphere. This is a slightly naive assumption given that the transport of the wood probably included diesel powered trucks and the planting and harvesting similarly fossil fuelled – but this is a small component in the overall mix. Looking at emissions per fuel source shows that wood is head and shoulders above gas, oil and other fossil fuel sources:
The installation itself took three days. It turns out Installing a Wood Burning Stove isn’t all that difficult or expensive. It involved (1) purchasing the stove (a Boru 600i Insert Stove) and a new, very well insulated hot water tank:
(2) taking out the old fireplace:
(3) Installing the new wood burning stove
(4) Installing the new tank, pump and plumbing:
We’ve had the stove for a year now. The stove has an output of 11kW to the hot water system (e.g. to heat the house) and 4kW to the room. I’ll be measuring it’s impact on the gas bill and will follow up with a post with exactly how much gas it’s saved us from burning, and hence, how fast it’s paying for itself. Right now, I expect this to be 4.22 years, after which it will provide a decent financial return in the form of very cheap, very low-CO2 heating for another 5-15 years along with cosiness on winter’s nights of which it is impossible to quantify financially.
 Carbon Dioxide Emissions of Various Fuels: http://www.volker-quaschning.de/datserv/CO2-spez/index_e.php “..if we only use as much wood as can grow again, it is carbon dioxide neutral because it binds as much carbon dioxide during growing as is emits during burning.”