Dear Umbra,
When changing boilers for heating a house for the next 30 to 40 years, should we choose gas or electric? We have gas now and want to go from 80 percent efficient to 95 percent efficient. About 60 percent of our electricity comes from Missouri River hydro and 40 percent from coal. We have wind, but that is not developed, and will only be a small percentage in the future.
Chuck Berry
Brookings, S.D.
Dearest Chuck,
Good for you for wanting to improve your efficiency, and for knowing in such detail where your power comes from.
Summer is certainly the time to think about replacing your old heating system. It's nice to be able to take the time you need to get bids from various contractors, research the most efficient boilers, drink some lemonade, and wonder whether winter truly exists. This year is a good year to do it, as well, because there are federal tax credits for certain very high-efficiency heating systems.
When considering boilers, think outside the walls.
Photo: iStockphoto
For the boiler itself, you'll want to look at Annual Fuel Utilization Efficiency numbers and talk to reputable local contractors (AFUE is a measurement of the fuel used to heat the house vs. the amount that gets vented out -- read about it and boiler shopping in another of my columns). In my area we can get contractor referrals from our gas company, so perhaps you can as well. Cost may make your decision for you. Electric boilers tend to be very efficient -- they can have an AFUE of up to 100 percent -- but heating with electricity can be expensive. Heat pumps are often recommended as an alternative to electric boilers. The highest AFUE I saw for a gas boiler was 95 (look at the U.S. Energy Star site for a downloadable list).
The question of choosing the fuel source for the new boiler is harder for me to answer. I won't guess at the future status of Missouri River hydro, the upcoming presence of wind in the power mix, and what will happen with coal-fired electricity generation over the coming years. I do think natural gas will become more expensive and less plentiful as fossil-fuel prices rise and gas usage increases.
Let's take a brief detour to look at how coal and gas stack up as sources of electricity (even though it's not immediately relevant to your particular situation). Natural gas is cleaner than coal on all fronts. Coal emits 2,249 lbs of CO2 per MWh, while natural gas emits 1,135 lbs per MWh. Even at 40 percent of the mix, coal's sulfur dioxide (future acid rain) and nitrogen oxide (future smog) emissions will remain higher per MWh over gas. In addition, we have the unknown amount of airborne mercury coming out of your coal plant. As for hydropower, it has not been known for its air emissions, until recent evaluations of the methane released by rotting plants under dammed and slowed rivers. I couldn't find any numbers on the Missouri, however, so we'll just have to vaguely consider it.
Hmm. I don't like the look of your electric choice, and I'm supposed to be giving advice. What I think is that you'll pencil out the costs, and won't want to pay for electric heat. If price is a non-issue for whatever reason, see what you can find out about the coal plant producing your electricity. It may have a campaign against it, for example, so you can read all about that, or it may be honored as the country's cleanest coal plant. Either way, I wager you can learn a bit more about the emissions specifics, and that will further tip the scales one way or the other.
Toastily,
Umbra
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Comments
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wayneluke Posted 3:40 am
22 Aug 2007
I would question though that if you are looking for efficiency improvements if there are other options than a standard boiler setup. Force Air may be cost prohibitive due to duct work, air returns and such but if you have HVAC, then it can share the same ducts. Another option would be a heat pump with "geothermal" based heat exchange. Or if possible infloor radiant heat.
Just seems to be more to the overall equation than just where the power is generated and what type of boiler to purchase, at least on the efficiency front.
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solar greg Posted 4:16 am
22 Aug 2007
Even bare pool collectors might work.
You might even benefit in summer by taking the heat off the roof.
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nycowboy Posted 6:22 am
22 Aug 2007
To say nothing of the fact that as you consume more electricity, more electricity has to be generated by burning coal, oil, or natural gas at other plants. Extra hydro or wind power can always be sent down the line or stored by pump storage until needed, but if you consume the extra electric now, the difference has to be made up by dirter (and more costly to run) power plants.
Look at adding to the natural gas boiler as many renewable and efficency choices as possible. Add more insultation to your house -- in the attic is an easy one. Look towards solar water heaters, planting trees around your house, building a burm around your house, etc.
Also consider wood if your in a rural area and can "grow" part of your energy source. While wood can produce a lot of particulate and other toxins, along with a substanial amount of global warming gases per heating unit (about 20x more carbon dioxide then natural gas when burned in a home woodstove), if your harvesting wood locally, it comes from a renewable source that will be a net carbon dioxide sink.
At my house we burn wood + an older dirty oil burner. By burning just a single cord of wood per year in our woodstove in the living room, we cut our oil consumption by about 40%. This cord of wood is produced by a healty and mature acre of forested land, from dead and down wood (not cutting down live trees). This forest consumes far more carbon dioxide in a year then we release by burning the dead and down branches/trees.
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amazingdrx Posted 11:18 pm
22 Aug 2007
Heat envelope systems that use 55 degree ground heat directly to render furnaces and boilers and even heat pumps completely obsolete are still in development.
Wait a few years for a heat envelope system if you can. It will retrofit onto the outside of your home. Install a solar domestic water heating system to reduce energy bills with renewable energy.
It is unecessarily pesimistic to assume that wind will not replace coal.
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Sean Casten Posted 12:32 am
23 Aug 2007
While it may make economic sense in a few regions of the country (e.g., if you're in a spot where your electric price is set by really cheap coal but gas is expensive), it is always going to be a bad idea from an environmental perspective. It is also eventually going to be a bad idea from an economic perspective - lots of New England homes were outfitted with electric heaters when the wave of nuke facilities was going up in the 60s/70s on the basis that the nuke was going to be "too cheap to meter". Nowadays, there is a brisk business in ripping out old electric heaters that have become too expensive to run.
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amazingdrx Posted 12:38 am
24 Aug 2007
With a heat pump drawing heat from the ground 3 times as much heat per unit of electricity consumed is collected to heat the home.
With a heat envelope system waste heat does the heating, while a low power electric circulating pump keeps a layer just below the surface of the building at ground temperature. It's like burying the whole building underground from a temperature perspective.
Going with the heat pump system now will facilitate a transition into a heat envelope system later. All powered by electricity that will eventually come from wind and solar.
Even if you are right that the grid will continue to be powered by coal, that heat pump system will produce less GHG and cost less than heating with ever more costly natural gas. Three times the heat output of even a 100% efficient combustion furnace makes that so.
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wyrick Posted 6:10 am
24 Aug 2007
Enough can't be said for demand-side efficiency improvements. After all, not using energy in the first place is the best option. To that end, the cost of a ground source heat pump system would certainly pay for a great deal of efficiency improvements to the house with more than enough money left over for a top of the line boiler while having a more comfortable home.
We know that 40% of Chuck's power comes from coal, leading to a 20% GHG reduction vs gas alone (40%*2x CO2 for coal) and the fact that total centralized generation and transmission losses are about 50% (ie. 2 kW produced= 1 kW delivered). Given that, the heat pump's GHG impact becomes much larger than first thought, albeit still 20% better than just burning gas. The point is that every situation is different and you can spend less money and have the same or better end result with a less glamorous solution.
My personal recommendation would be to insulate and air seal my your first and then buy a Viessmann Vitodens boiler to replace the boiler and hot water heater if there is one.
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