This post was originally published January 9, 2009, at http://www.towseyfrench.com.
Leave it to a Portland energy geek to ponder the electrical impact of his family’s wood stove –as if thinking about the carbon impact of burning wood was not enough. Whatever the case, that’s exactly what’s been buzzing in my bonnet these days.
Heating your home requires fuel, and in most cases, a means to transfer the heat generated by burning said fuel throughout your home. Subsequently, when calculating the cost of the fuel (e.g., natural gas, biodiesel, wood, oil, etc.), it’s important to factor it the cost and quantity of electricity needed to distribute heat throughout your home. If you utilize a forced-air furnace, you are consuming electricity, regardless of your fuel source, adding to your carbon footprint. In the grip of another Oregon winter (albeit quite tolerable these days), I made the decision to share my findings in calculating the carbon footprint of my family’s cast iron wood stove fireplace insert.
The Vermont Castings WinterWarm (small) cast iron fireplace insert is an age-old heat source given a ‘green’ lease on life with the addition of a clean-burn catalytic converter (similar to that in an automobile), ensuring slow, super-clean fuel consumption. When the converter is actuated, there isn’t even a hint of exhaust from the chimney. While we hand-picked this stove due to its impressive carbon credentials, I failed to properly vet the stove’s electrical consumption –also a key element of the stove’s energy consumption.
The WinterWarm uses two blower motors which are listed in the installer’s documentation as capable of pumping 110 cfm (cubic feet per minute) of air into the living space. These blower motors feature fans with extremely tall gears, as indicated by the long roll-up time to achieve maximum output, generating an experience akin to a jet engine firing up (albeit much quieter and far less dangerous). Air is pulled from around and below the stove, then pushed up over the top then out the front of the stove directly next to the activation arm for the catalytic converter.
Mind you, the motors/fans are somewhat noisy and inaccessible unless the stove is removed from the fireplace chamber. This means maintenance will be a challenge, but if all goes well, a rare occurrence. It’s also important to note that the fans produce much more noise when the stove has yet to reach optimum operating temperature. The hotter the stove gets, the quieter the fans. I attribute this to the flex of the cast iron and steel fan shrouds, loosening some of the naturally high tolerances of the fan housing –but this is purely conjecture.
The manufacturer does not list the energy consumption of the electric blowers, though the dealer we worked with claimed it was nominal due the high gearing of the motors. The dealers I contacted also claimed to not have ready access to the energy consumption figures. Several calls to Vermont Castings and their Canadian parent company (Monessen Hearth Systems Co.) yielded little assistance, consistently directing me back to the dealers. This is unfortunate as the dealers didn’t have access to any additional information.
Fortunately, one of my co-workers owns a Kill-a-Watt electrical consumption analyzer, which said co-worker so generously loaned to me. The Kill-a-Watt is simple to use and generate immediate data on the electrical consumption of any appliance with an Edison-style plug. It’s also the perfect tool for analyzing the ‘phantom’ consumption of appliances and electrical components that are plugged in but not actually turned on. Using the Kill-a-Watt, I acquired the following consumption data for the wood stove:
- 120.5 Volts
- .42 Amps
- 36 Watts
- 59.8 Hz
Utilizing this data, I calculated that at 16 hours of use per day (average), the stove consumes .576 kilowatt-hours per day (kWh). This translates into apx. 17.28 kWh per month. At 6.2 cents per kWh (the peak rate), this stove will cost $1.07 per month to operate. This is far more efficient than our furnace, which –though fully modernized and modified for modern B99 burning– still utilizes a pre-1990 forced air blower (this needs resolved soon).
While this is excellent information for helping determine the actual cash value of using the electrical blowers built into the stove, I’m also quite interested in understanding the carbon footprint of said electrical consumption. To understand this, we need to know exactly what a kWh is, as well as what it means. Fortunately, the Web is littered with smart people who have spent inordinate amounts of time doing the math.
First, note that a kilowatt-hour equals 1,000 watts of electricity for one full hour. That’s essentially equal to operating ten 100-watt light bulbs for one hour -or- one 100-watt light bulb for 10 hours. For each kWh produced with fossil fuel, approximately 1.5 pounds of CO2 (0.68 kilograms) is released into the atmosphere. For the Vermont Castings Winterwarm (small) cast iron fireplace insert, that translates into 25.92 pounds of carbon per month, at 16 hours per day of use –just slightly more carbon than burning a gallon of gas in a typical modern automobile. This is, of course, if your electricity is produced entirely through conventional means (e.g., coal and natural gas).
It’s important to note that the average American household uses approximately 700-900 kWhs of energy every month. In 2006, the average was 920 kWh per month (US Department of Energy, Energy Information Administration). A policy release dated February 26, 2007, noted that, “The average household in America consumes 10,656 kilowatt-hours (kWh) per year, according to the Department of Energy.” Divide that figure by 12 months and you average 888 kWh per month. To put this in perspective, that’s about 1,300 pounds of carbon (again, if generated using traditional means).
Perhaps it’s my inability to appreciate energy consumption based solely on the somewhat esoteric methods provided by our utility companies. Whatever the case, I can’t help but think that it might be more beneficial in helping consumers understand and thereby manage their consumption if we were charged for electricity in pounds of carbon, as opposed to kWh. After all, we buy cheese and fish by the pound, why not energy?
{ 2 comments }
We had a similar insert, and I had similar questions about the fans, but principally hated the noise they made. We had a catalytic woodstove before and liked just hearing the fire noises. Plus the quality of radiant heat from the stove makes the room feel warmer much quicker than the convected warm air from the insert.
Emails to the manufacturer were never answered. I pulled out the stove and put in synthetic rubber isolaters for the fan motors to quieten them: didn’t do much, most of the noise appears to be radiated from and through the sheetmetal shrouds. So I put in quieter a/c fans and new ducting: it was quieter, but still not how I wanted it. So the insert is now for sale, and we reinstalled the old woodstove which comes out into the room too much but heats great. (and zero fan $ : we have a bimetallic strip-driven fan on the stove that generates its own power off the heat from the stove…)
@Jonathan Woodbridge – No doubt, Jonathan, stand-alone wood stoves are superior for total heat output and efficiency. An insert, while leaps and bounds more effective than a fireplace, still loses a good degree of radiant heat into the firebox, and then the chimney. A free-standing stove simply radiates said heat directly into your living space without any need for forcing air around the stove.
We considered a free-standing stove, but the massive footprint required would have destroyed the aesthetic of our bungalow’s living room. Additionally, with two children below the age of 5, it would’ve proven challenging to keep little hands free from scorching, even if we had the space!
Our intention has been to ‘augment’ our B99 biodiesel forced-air furnace with wood, but we have actually relied on the insert far more than anticipated. It’s effective and far less expensive to operate than the furnace. True, the furnace is simply far more effective at heating our home overall (the insert doesn’t heat the whole house), but the insert does a great job in helping us keep the thermostat turned wayyyyyyy down.
This being said, if you have a space that is conducive to a free-standing cast iron stove, they are superior heating devices, often generating enough heat to peel the paint off your walls. It’s an easy way to turn your home into a sweat lodge in no time.
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