This article was originally published in the July/August 1996 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.


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Home Energy Magazine Online July/August 1996


Where Do Average Costs Come From? In energy cost calculations, 8.25 cents/kWh is often used as the average cost of electricity. This figure appears low. Consumers in the major population centers such as the Northeast and California are paying considerably more. 8.25 cents/kWh may show what the average utility is charging, not what the average consumer is paying.

If the editors or readers have any further information on how this figure is calculated, perhaps they could clarify this point.

Larry Schlussler
Sun Frost
Arcata, CA

Editor's reply: There are many ways to average electricity rates. The most often quoted average is from DOE's Energy Information Administration (EIA). Their most recent average is 8.41 cents/kWh for 1995. They get this number by dividing total residential electric bills by total residential electricity use. The EIA also projects an average rate for the upcoming year. For its EnergyGuide labels, the Federal Trade Commission uses the EIA's projected rate for the year. Current labels assume a rate of 8.67 cents/kWh, which the EIA estimated for 1996. They projected 8.4 cents/kWh for 1995.

The National Association of Regulatory Utility Commissioners (NARUC) calculates a different average rate. NARUC takes the rates that residential customers pay in each of about 190 service areas nationwide and averages them, without regard for population or usage in those regions. Their average residential rate among the service territories for winter 1994-95 came to 9.1 cents/kWh.

Neither of these gives us what the average customer is paying. The EIA method is an average out of the total electricity sold, so the rates of customers who bought more electricity count more toward the average. The NARUC rate shows what the average utility is charging. We don't know of anyone who calculates what the average residential customer is paying.

Average rates are often used to give advice about what energy source to use or what energy-saving measures to implement-advice that may be misleading, due to local price differences. Local rates should be used whenever possible to estimate energy costs and savings. But a national average can be better than nothing when researchers and others need to pick a rate for estimating costs or savings from measures or technologies that are available nationwide.

Mildew on Composite-Board Siding We would be interested in hearing what corrective options readers have employed when confronted with severe, recurring mildew on composite-board siding over polystyrene sheathing. Obviously, we are talking about existing construction and what can be done to eliminate the moisture trapped between the siding and the sheathing.

Harold L. Crowder, Jr.
Virginia Power
Richmond, VA

Editor's reply: We asked Joe Lstiburek of Massachusetts' Building Science Corporation to respond to your question. You are not alone in your concern about compressed-wood siding. In fact, there are lawsuits in progress all over the United States against the makers of various composite wood sidings.

In composite-wood sidings, wood is compressed to about double its normal density and is not well enough sealed at the edges to prevent moisture uptake. Once the moisture gets in, the wood starts to swell; in time, it expands back to its original density. If the problem has gone this far, the siding must be removed and replaced. Remove the composite wood and install new siding on furring strips for spacing. Be sure the new siding is back-primed and the field cuts are sealed with paint. Just butting the ends together and caulking doesn't work.

If the problem has not gone too far, however, the following steps can help keep moisture out of the existing siding. First kill the mold and mildew with a solution of bleach and water. Then recoat or paint the bottom edges of the siding (you must brush rather than spray the paint on for it to seal). For worse cases, loosen the siding with a flat prybar (called a Wonderbar) and insert plastic siding wedges (available from Hyde Manufacturing in Southbridge, Massachusetts) by each nail. This creates a tiny air space that vents the backside of the siding, allowing it to dry. Again, the bottom edges must be painted or treated to seal the pores that allow water uptake into the material.

The manufacturers have made attempts to seal or protect the edges of the newer compressed wood products, but I recommend against using even these new products. If you do install them in new applications, install spacers to create space between the laps and the backside of the siding.

Due to widespread problems with moisture damage, class action lawsuits are under way against several composite-wood siding manufacturers, including ABT, Georgia Pacific, and Masonite. Louisiana-Pacific's Inner-Seal has already settled a $375-million case with homeowners.

Canadians Blew It First I enjoyed reading the article about blower doors (The History of the Blower Door, Nov/Dec '95), but felt that it overlooked some of the earlier Canadian contributions. In 1975, two Canadians, George Tamura and Sol Stricker, presented measurements of air leakage characteristics of houses at an ASHRAE conference. An even earlier (1973) paper by John Shaw, Dan Sander, and George Tamura, also Canadians, presented air leakage measurements of the exterior walls of tall buildings.

I haven't surveyed all the technical papers in this area, but the work of these Canadians predates the 1977 work of the Swedish researchers mentioned in the article. A good summary of papers on the subject is presented in A Subject Analysis of the AIVC's Bibliographic Database-AIRBASE from the Air Infiltration and Ventilation Center in England. Perhaps one of your readers might know who performed the first-ever whole-house air leakage test.

Rob Dumont
Saskatchewan Research Council
Saskatoon, SK

Opening Up to 
Fireplace Dampers In the May/June Letters, John Morrill questioned the requirement that fireplace dampers be secured open when gas logs are installed. You noted that the Uniform Mechanical Code (UMC) generally prohibits dampers in the venting systems of gas appliances, and speculated that an interlock might be used to prevent operation of the logs should a manually operated damper be left closed.

In fact, there are specific, inflexible rules mandating open dampers for gas fireplaces. These are in the UMC as well as the One and Two Family Dwelling Code (OTFDC) and the International Mechanical Code (IMC); a corresponding rule exists in ANSI Z21.60, the testing and listing standard for these devices. Therefore, a safety interlock or automatically opening damper such as you suggest would be unlikely to be approved.

Besides, the use of a retrofit device designed by a third party would violate the terms of listing and manufacturer's instructions for the gas logs, exposing the installer to liability.

Gas log makers are aware of the energy penalty of the fixed-damper approach to safety, and want to develop an interlock to prevent gas from flowing with the vent closed. Unfortunately, the lack of an option in the current code reduces manufacturers' incentive to develop a device.

I went to the first hearings for the 1996 revisions of both the OTFDC and the IMC. On behalf of the Hearth Products Association, I submitted a proposal to both codes to allow an interlock. The device would have to be incorporated into the appliance design, tested for equivalent performance under the ANSI standard, made a part of the appliance package, and installed according to instructions.

We received committee approval for the OTFDC version of our proposal, but not for the IMC version. The IMC committee objected that such devices are not currently available, and that the code should not anticipate speculative devices.

The next step in the IMC code development process is a challenge round, where the membership of the three major code bodies can vote to override the committee. I would appreciate expressions of support (or other comments) from the energy conservation community.

David Johnston
DSJ Technical Services
Wooster, OH

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