Hot Water Options

Q: I just read the article titled "Water Heaters and Energy Conservation--Choices, Choices!" from the Home Energy Web site, dated May/June '96. I am an architect working on a residential remodel project. My clients want on-demand water heaters. One of them has a small, electric on-demand heater (Instant Flow by Chronomite) at their office and really likes it. Do you have any information on this product?

The clients currently have an electric water heater, located in the basement, that is due to be replaced. We are considering replacing it with a new gas tank-type heater and possibly putting a tankless heater in the bathroom on the second floor, just for the sink. (The water heater is about 25-30 ft away from this bathroom.) I should mention that they are interested in using low-maintenance products.

I am curious about the efficient, recirculating demand system, made by ACT Metlund Systems, that was mentioned in your article. Where can I get more information about that? Are tankless electric water heaters worth considering at remote locations?

Ann Costello, Architect
Environmental Works
Seattle, Washington

Larry and Suzanne Weingarten, authors of the 1996 article, respond:

This electric tankless water heater provides hot water on demand.

A: Here are two approaches that might work for your clients: First, consider a small electric tank-type heater run on 115 volts, alternating current, located in the bathroom, being fed by the main gas-fired water heater. This would deliver quick hot water (for both sink and shower, if properly piped); it probably would not require running a new electrical circuit; and it would be low maintenance. Also, standby heat loss would be quite low. The advantage here is that you get quick, uninterrupted hot water at modest cost; this slightly raises power consumption, but it increases performance and saves water.

A second approach would be to install a Metlund demand system. This system pumps cooled water from the hot plumbing into a cold line, pulling hot water from the water heater to fill the hot-side piping. It operates only on demand, at the push of a button. You would install this in conjunction with the main gas-fired water heater, eliminating the need for a second heater in the bathroom. This would be more complex than an electric tank-type heater, but if placed correctly, hot water would be available quickly at all taps, not just in the bathroom.

Although recirculation is usually a time waster, it is typically the first choice for solving this type of problem; this is the most efficient recirculation system that is available, and it has the advantage of simplicity (no thermostat or timer). You could consider an electric instantaneous heater for individual sink use, but it would not be well suited for supplying a shower, too.

You mention that your clients are interested in low-maintenance products. Compared to tank-type heaters, gas and electric tankless units cannot be called low maintenance (see the sidebar in our original article, "Tank-Type Versus Tankless," p. 17). This is because they have more moving parts and/or controls, and some may need deliming in hard-water areas. Thus, tankless may not be the best choice.

Finally, don't forget to put heavy insulation on all the hot water piping you can access.

Q: Our electric tankless water heater is not capable of booster-heating the water that is preheated by our solar panels in low-solar months. The water gets kicked into the system from groundwater temperature (supposedly 55°F), circulates into the solar system, then recirculates down into an insulated standing solar tank, where it is called into action when I turn on the hot water faucet. The water comes into the coils of the tankless heater and then up through the faucet. For about four months of the year, I can turn off the electricity and bypass this tankless unit, using only the sun to heat water for us. But from November until mid-April, we always struggle to get hot water. I have had the heater checked with a volt/ohm meter and it is working, but still our water does not get hot enough even to wash one's hands. So, I have to heat the water in a pot and on the gas stove in order to wash the dishes. Haven't had a warm shower since Thanksgiving! We are thus thinking of canning the whole system and reverting back to a conventional water heater.

My questions are: Should we replace the solar tank with a conventional electric one? Should we keep the system the way it is now, but replace the tankless heater with an electric tank heater? I assume that this way, the solar unit would continue to function and just preheat the water before going into the electric tank. Then, would we have to adjust the dial depending on how hot/long the sun was shining? Is there an electric water heater than can handle preheated water from a solar system, or must it get cold water from the well or city? Out here in the boondocks, we have access only to propane gas, and that is very expensive at more than $2.69/gallon. (It has gone up 20¢ every three months just this past year!)

MaryJo Laughlin
Lebanon, Pennsylvania

Larry and Suzanne Weingarten, again:

A: Let's start by figuring out how the different energy costs compare: Energy cost times efficiency equals performance. Tank-type heaters have an energy factor rating (see the big yellow sticker), which is essentially a percentage of efficiency. It tells you what percentage of the heat you pay for actually gets put into the water. Electric tank heaters range from roughly 85% to about 95%, while good gas tank heaters range from 60% to 62%.

Now you need to know the cost per unit of heat for propane and electricity. A gallon of propane has about 91,300 btus. A kWh has about 3,413 btus. So, propane costs you about 34¢/therm (a therm equals 1,000 btus). Electricity, guessing it costs you 12¢/kWh, would be about 28¢/therm. Divide that by the efficiency of the heater, and you get the cost per delivered therm. It is a good way to compare different heaters.

Next, look at level of satisfaction. What is a hot shower worth to you on a frigid morning? What is a cold shower worth? Either a gas or electric tank-type heater would give you a decent shower. Temperature adjustment is not a concern: The heater's thermostat will heat only as much as is needed over what the solar delivers, or will do no heating at all if the solar is hot enough. So, the suggestion is to keep the solar (do check the anode in its tank), but replace the electric tankless with a tank-type heater, probably electric. If the electric tank is located indoors, any lost heat will warm the house.

By the way, are you able to shop around for a different propane supplier? You may be able to find a lower price.

Larry and Suzanne Weingarten operate Elemental Enterprises in Monterey, California; the company services conventional and solar water heaters.

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