This article was originally published in the January/February 1995 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.
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Home Energy Magazine Online January/February 1995
More Waterbed Data
I was dismayed after reading the article on waterbed heating that you did not use data from the Residential Energy Consumption Survey (RECS) relating to the energy use of waterbed heaters (see Waterbed Heating: Uncovering Energy Savings in the Bedroom, HE Sept/Oct '94, p.41). Do your readers know that this triennial survey of households covers many important uses of energy in the home? For example, the 1990 survey documented that 14.5% of U.S. households use one or more waterbed heaters (11.6% have one and 2.9% have two or more). The 16.9 million waterbed heaters were estimated to use 2% of the residential consumption of electricity in 1990. These and many other data are available in publications of the Energy Information Administration that report the results of the RECS.
Data on low-E windows, aquariums, air cleaners, home faxes and copiers, various types of fans, lights used more than one hour per day, use of outdoor lights, and participation in demand-side management programs are some of the new topics available from the 1993 survey. To get these data, call (202)586-8800, or use your modem to sign onto our electronic bulletin board at (202) 586-2557.
How timely your article on waterbed heaters was. Our agency operates a low-income weatherization program, and during the last year has begun a new emphasis on energy education. Just today, a colleague provided me with a report on a low-income, payment-troubled family who unplugged their waterbeds as part of our Weatherization Assistance Program follow-up energy education.
As a result of weatherization, switching the water heater from electric to gas, and energy education about the cost of operating waterbed heaters, the family reported their lowest electricity bill ever. Their electric bill last August had been $130.67 but this August was $67.60. Electric usage went from 1,146 kWh to 759 kWh. In part because the waterbed was unplugged, the family now has both a greater sense of energy use and more money in their pockets.
I found the article on advanced-combustion fireplaces to be informative, but I still have a number of questions regarding the technology (see Fireplaces: Studies in Contrasts, HE Sept/Oct '94, p. 27). Many new fireplaces and woodstoves advertise efficiencies better than 80%. This would seem impossible, given Skip Hayden's maximum of 78% efficiency with minimal excess air. Are they advertising combustion efficiencies or true total efficiencies? Do they reflect realistic usage?
How do fireplaces and woodstoves compare to coal-, oil- and gas-burning equipment, in terms of cleanliness?
What are the constituents of incomplete wood combustion products? Are there significant amounts of dioxins or other carcinogens?
Do the new units really burn cleanly when their air supply is choked down to reduce heat output and prolong burning?
My main concern is that even with the new technologies, burning wood may produce pollution that is out of line with the lower levels we we require from automobiles and boilers.
Author Skip Hayden responds: Table 1 in that article was designed to show that excess air has a dramatic effect on the maximum efficiency attainable. The fact that I listed no efficiencies above 78% does not mean you can never have a system with a higher efficiency. Indeed, if I ran at an excess air level lower than 100%, or if I took more heat out within the appliance so that my flue gas temperature was less than 300deg.F, or if my wood had a moisture content less than 17%, my stove would be more efficient. On the other hand, all of the other characteristics (as stated later in the article) of the advanced-combustion fireplace have to be there in spades for the real seasonal efficiency of the appliance to be at or above that level.
As for pollutant emissions, NOx emissions tend to be lower with wood, and carbon dioxide (and hence greenhouse emissions) can be considered zero to the extent that the wood is harvested in a sustainable fashion. Conventional wood stoves have high levels of incomplete combustion products, including carbon monoxide, hydrocarbons, and condensible organics (in the form of PAHs, carcinogens similar to those in cigarette smoke). Indications are that in advanced technology stoves, all of these emissions have been reduced by 80% to 90%. There is no evidence that there are significant levels of dioxins in these advanced-combustion systems.
The new units burn cleanly even when run at low fire. Indeed, some designs actually burn their cleanest at that point. To meet the emissions standard, they must have a clean low burn, so they cannot be as completely choked off as could the dirty stoves of the 1980s. Furthermore, the viewing window allows the operator to see when combustion is optimum--he or she tends to keep it there because the flame is prettiest at that point, as well as being more efficient.
The continuing evolution of this alternative to the outmoded fireplace will permit an environmentally benign use of renewable energy.
Where to Find Efficient Wood Fireplaces?
Would you be kind enough to send me a list of manufacturers of advanced combustion wood-burning fireplaces meeting the EPA 1990 or CSA B415 performance standards?
Evan W. Fletcher
Editor's Note: For a list of Environmental Protection Agency-certified wood heaters that includes emissions rates as tested, default efficiencies, and BTU ranges, contact EPA's Manufacturing, Energy and Transportation Division, 22-23A US EPA, 401 M St. S.W., Washington, DC 20460, Attention: Wood Heater Program. The list is available at no charge. A list of certified comfort conditioning equipment, which includes advanced-combustion wood-burning fireplaces, is available from the Canadian Standards Association for (Can)$20. Contact: CSA, 178 Rexdale Blvd, Rexdale, Ontario, M9W 1R3. Tel: (416)747-4044; Fax: (416)747-2475.
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