Letters: January/February 2009
Where’s the High-Density Foam?
I was looking over your article in the Nov/Dec ’08 issue (“The Long Island Green Homes Program,” p. 6) and noticed that the description of the picture on p. 8 is incorrect (see photo below). In the rim joist I can see a kraft-faced Certain-Teed fiberglass batt installed, not 4-inch high-density foam. On the facing of the kraft-faced material it notes you cannot leave this material exposed because it’s flammable.
David C. James
Santa Barbara, California
Author Rich Manning replies:
That is a good observation, but let me explain. The foundation is an 8-inch concrete block wall and the house was built in the 1920s; therefore it had balloon framing. The picture that I took was taken before the work was completed. We had sprayed 4 inches of high-density foam along the rim joist, not only to insulate the rim joist and underflooring, but also to use it for fire blocking. We wanted to finish it with the Thermax so it would look uniform and not be recessed, so we filled the space between with fiberglass to fill the void and help slow down air movement. It doesn’t matter if it is faced or unfaced, since it was going to be covered. All that was available at the time was faced fiberglass, so that was what we used. We then covered the fiberglass with Thermax up to the bottom of the flooring to seal off the floor bay in a straight line for cosmetic reasons. I didn’t show that picture because I wanted to show the rim joist with the high-density foam, but I got there too late and after they had installed the fiberglass.
Hope this helps!
Ad Tone Found Disagreeable
I just received the Nov/Dec ’08 issue of your fine magazine. In the center is a four-page ad that concerns me. There are many statements that are inflammatory, including some that bend the truth. Just one example is in the middle of the second page: “The three major manufacturers [of fiberglass] keep the fibers long in order to enable contractors to make huge profits by cheating the homeowner.” This accuses three very large corporations of fraud right from the start of manufacturing their product! In the first paragraph alone, the author uses the word “cheating” five times, along with “fraud,” “misrepresentation,” “expose,” “crooks,” “opportunistic feeders,” and “scandal,” and this language and emphasis continues through four remarkable pages.
This infomercial, complete with capitalized and underlined highlights, has no place in a professional trade journal and is beneath the magazine. I feel you should have emphatically turned down this ad.
Ed Minch, Energy Services Group
Publisher Tom White replies:
Thank you for your recent complaint about the 4-page ParPac advertorial insert in the Nov/Dec '08 issue of Home Energy. I share your concern about publishing opinion cloaked in advertising, and I apologize for this oversight. As a result of this incident, I have initiated a new policy at Home Energy: we will not accept or publish infomercials, advertorials, or other editorial content, opinion or commentary submitted as advertising by outside parties.
I greatly appreciate the loyalty of our readers and encourage all Home Energy readers to be as vigilant and outspoken in sharing their concerns. Thanks again for sending your comment—I take your complaint very seriously and will be equally vigilant in my new role as publisher.
Tom White, Publisher
Tankless System an Unpleasant Surprise
To lower our heating bills we installed a tankless water heater to replace our old (still approximately 80% efficient on test) direct oil-fired boiler. Our problem relates to water heating for domestic use, not to space heating at all. All our clothes are washed with cold water, we do not use a dishwasher, and we have only two teens—instructed not to take long showers—at home.
We were impressed with a boiler and indirect system efficiency but scared by the installation cost (approximately $5,500–$7,000). As a result we installed a propane tankless system (natural gas is not an option here), but the daily cost is staggering!
The technician from the local propane supplier stated that our new tankless system delivers “a maximum output of 200,000 Btu but probably delivers around 110,000 Btu with average use.” He says that this means that if we ran the water-heating system for an hour at full capacity, we would consume about 8 liters of propane. Our average use per day actually works out at 5.4 liters per day. Is it possible that the heater is working at its lowest possible capacity, yet exceeds our hot water demands and therefore wastes a great deal of energy? In others words, will the heater use the same amount energy if someone uses a low rate of flow (such as for brushing teeth), as a high rate of flow (such as for washing dishes), over the same period of time?
By contrast, in the case of a hot water tank, the low rate of flow would release less thermal energy from the storage tank than the high rate of flow, making the tank system relatively more efficient. If that logic is valid, should we investigate the installation of a smaller unit than we have currently? If we look into buying a smaller tankless system, where can we obtain a table that would estimate the daily Btu requirements for our family? I would use the 5.4 liter figure, but obviously I am under the impression that we use fewer Btu than is contained in 5.4 liters of propane.
An indirect water heater (using a boiler) is touted as the most efficient system for water heating by our local plumber, but I cannot get my head around why the system is inherently more efficient than the conventional direct tank system, except that one can insulate the (indirect) tank so well because it is separate from the burner. Can you help me to clarify this issue?
With all the resources at hand, it still is almost impossible to decide what to do. It is hard to compare apples to apples, and dealers hedge on that to provide one with trustworthy quotes. Do you think we should bite the bullet on the indirect system and if so, should it be propane or oil? Propane seems to be less costly than oil in eastern Canada because many are switching to natural gas; oil prices are climbing more rapidly than the former.
What to do! Cheers for now.
Charlottetown, Prince Edward Island, Canada
Technical Editor Steve Greenberg replies:
The efficiency of the tankless hot water system should be better than the oil boiler/indirect system, so if the fuel is cheaper, you’re saving money (if usage is constant or lower than before). Be careful when comparing propane to oil, because propane contains only approximately 91,000 Btu per gallon while #2 fuel oil is more like 140,000 Btu per gallon. So the fuel price per Btu and the conversion efficiency of the water heater (or boiler or furnace) both matter in terms of delivered cost per Btu. The final cost depends on those two, plus the amount used, which in turn depends on the efficiency of usage (such as gallons of hot water per minute), and personal behavior (minutes of use).
To answer your question about energy use for low flow rates versus high flow rates, the energy use is not equal. The heater will automatically adjust the gas input in an attempt to heat the flow to the desired temperature. If the flow is too low to maintain temperature control (that is, the water would be too hot), the unit won’t turn on at all. If the flow it can handle is exceeded, it will lose temperature control (that is, the water will be below the temperature setpoint), but it will continue to fire at maximum input.
In figuring out your options, it may well make sense to use 5.4 liters per day of propane. Yes, it is possible you really are using that much heat. At 80% system efficiency, that’s about 100,000 Btu delivered to the water, which is enough to heat about 200 gallons by 60ºF—for example, from 50ºF to 110ºF. Here’s how to calculate the Btu delivered:
Btu = gallons of delivered hot water x temperature difference between cold water and delivered hot water in ºF x 8.34 Btu/galºF. Then divide that by the efficiency of the water heater (typically around 0.8) to get the Btu input to the heater.
You’ll need to estimate your gallons of water and measure your temperature difference to use the above formula.
If the existing heater is able to turn on at the lowest desired flow, and doesn’t overheat the water, there’s no good reason to use a smaller heater.
An indirect water heater would be more efficient than a tankless system only if the boiler was more efficient (this is possible, since condensing boilers with efficiencies above 90% are available). It almost certainly would be more efficient than a gas-fired storage tank system, since the standby losses of the open-flue tank are very high.
You might consider water- and energy-saving devices such as faucet aerators and low-flow showerheads, if you haven’t invested in these already. Aerators save energy by slowing flow rate. The aerator also helps the lower flow wet surfaces better. Low-flow showerheads are very cost-effective, and many very good models are available that give excellent shower characteristics with less water and energy.
Another technology to consider is a wastewater heat recovery unit (see “Drain Water Heat Recovery Devices,” May/June ’08, p. 34). These can cut the energy use of a shower in half.
Jim Lutz, research scientist at Lawrence Berkeley National Laboratory, adds this comment:
The only thing I would add is that because the tankless water heater only turns on when water is flowing, as soon as the water stops flowing, it turns off. Any residual heat left in the heat exchanger and small amount of water in the heater dissipates and is lost. That means for tankless water heaters, short draws are less efficient than long draws. If there’s a lot of short draws, the efficiency of a tankless water heater may be 8%–10% lower than rated.
An error was made in the editing process for the article “Do CFLs Save Whole-House Energy?” in the November/December ’08 Home Energy (p. 20). In Table 2, Energy and Cost Savings Associated with CFLs, on p. 22, the space heating increase for Miami, Florida, should be 0 kWh.
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