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Is a Tankless Water Heater System a Wise Choice?

By Scott Sklar
August 31, 2006 | 9 Comments

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I am researching tankless hot water heaters to replace my traditional unit. My house has all electric, no gas. Basically, are electric tankless systems efficient? -- Brian D., New Market, MD.

Brian, Tankless water heaters penetrated the European market way before the U.S. According to Rheem, headquartered in New York, a 64-gallon per day system (around 9 cents per kilowatt-hour) should cost you around $460 per year. The theory is that you are only expending energy to heat water 'when you need it' thus no need to store water and keep it warm. Overall this is true. On the other hand, conventional solar water heating systems, particularly thermosyphon or those using pv-powered circulation pumps, require no (or minimal) input of electricity -- and in my home, need no backup with a super-insulated water tank. Other types of water heating systems using waste heat from furnaces (in winter) or from ground-coupled heat pumps can also be very efficient. For those sticking with conventional water heaters, at least purchase insulating blankets sold in the major hardware chains for your water heater, to keep the heat in the tank, not in the air. Depending on whose data you use, from 10 to 15 percent of the energy in your building is used to heat water -- so carefully selecting energy systems will save you money in these times of steeply rising natural gas and electricity rates. - Scott Sklar

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9 Reader Comments

Comment
1 of 9

frank-baumgardt-15272

August 31, 2006

Having grown up in a house with an electric tankless heater, I know that there are other issues to consider. E.g., the heater only kicks in over a certain waterflow, so it is difficult to get little but hot water. Also, if you have other appliances (sink or so) use the same water heater, the water temperature will fluctuate pretty wildly when the second use is turned on. I assume the technology hasn't changed all that much over the years, but could be wrong.

Comment
2 of 9

philip-leen-55408

August 31, 2006

I agree with Scott, that electric tankless heaters are not the best solution for only electric, as solar would certainly be the first choice. Electric tankless are a good choice in the extra bath with just handwashing sink, or for a warehouse sink, but for the full load it is best to look at solar, and conservation additions,. Depending on water demand, a timer can be utilized to turn the tank off in the middle of the night, and when leaving the home. Of course a good insulating cover is very important, as well as the hot water piping, including the T&P valve, and if there are long runs to an outlet, insulation and a circulating pump can be installed.

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3 of 9

paul-button-53997

September 14, 2006

I have had gas-fired tankless water heaters in the two homes i owned. (Aquastar, both).
the water flow ignites the flame, etc...
the only lifestyle change that had to get the kids to do was to not keep turning the water off and on. just get it hot and then lower the pressure, but leave it running.
the on/off/on/off caused the pilot to snuff, due to blowback of the main burner.
if i would whine about anything, it would be that Aquastar (now Bosch) never replaced the pilot with an IID, or piezo device.

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4 of 9

robert-kasman-27543

September 20, 2006

To answer your original question more directly... all electric water heaters (tank or tankless) are essentially 100% efficient in the conversion of electricity to heat. Contrast this to natural gas water heaters where over a third of the heat generated by combustions is vented out the flue. (The exception is for natural gas condensing water heaters.) All storage tank systems have some stand-by losses, but new tanks are fairly well insulated to minimize these losses. In terms of efficiency between a tankless electric and storage tank electric, the only difference would be in stand-by losses, and that would be a small difference. Regardless of your choice, reducing hot water consumption through low flow show heads, faucet aerators, efficient appliances, etc. will be your most effective strategy. Saves water too.

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5 of 9

allen-gordon-16697

September 20, 2006

The issues I face with tankless water heaters is that I live in a rural area and the water from my well is at 50 degrees or so. I also have an all electric house with no propane. The largest single circuit electric tankless heater (30 amp) does not raise the temperature sufficiently so I had to put in a mixing valve to mix some of water from hot water tank with the cold water prior to the input of the tankless heater. An electric tankless heater large enough to raise the temperature of my well water would require 3 circuits or about 120 amps. I also have an outdoor wood fired boiler that I use for my radient heating system. I've put in a heat exhanger into the loop that convectively heats the water in my hot water heater, so that the hot water heater is using far less electric power.

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6 of 9

bill-berry-56893

October 11, 2006

In shutting my water heater off while at work; the temperature drop off is minimum...from 110 to 106 in course of an 8 hour day, irregardless of what time of year, what indoor/outdoor temperature it is. I just don't get how a tankless system for a family of 4 saves electricity overall, not when it's draw is higher than my all electric furnace (23 KW per hour). All this said, we use low-flow nozzles, insulation wraps, caulk and expanding foam wherever possible. And if power goes out, what then? There isn't a generator alive that can run this system; but can a conventional water heater; something to consider if you live in an area that loses power depending on the type weather you may experience. And don't forget some power companies, like Alabama Power offer rebates & credits on tank water heaters.

Comment
7 of 9

bill-berry-56893

October 11, 2006

When I do the math, I don't see how a family of 4 saves money using a tankless water heater. My current water heater uses 5676 watter per hour, where a tankless system uses up to 28,000 watts and as high as 32,000 watts per hour depending on the system you use. We average 125 to 150 gallons of well water use per day or about one hour of use if we had a tankless water heater. I've tested at the electric meter with and without using the water heater, and the differences are even close to make me warrant buying a tankless system. That's not counting upgrading my circuit breaker box to accomodate the amperage increase, let alone the wiring to accomodate it. Something to be said, when you can buy a tank install it yourself without retrofitting your home.

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todd-bauswell-71425

September 14, 2007

I am having a tankless water heater installed.  I have well water without a softener or filter, is this going to cause any premature problems with the unit?

Comment
9 of 9

littlebit

January 29, 2011

I will never get another tankless water heater. We have had nothing but problems. We have well water and the hard water has corroded the tankless water heater unit. We thought we had an eight year warranty with Renai but when they found out we had well water, they would not stand behind their warranty. So if on well water, check out the warranty on the unit you are purchasing. Also, the tankless water heater never really gets hot and the temperature fluctuates. In the long run, we have wasted a ton of money on a tankless unit by having our house retrofitted to accept the tankless heater, spent money to have gas run to the unit, endless repairs and the initial cost of the unit itself. And just the hassle of not having hot water during this whole time. I would not recommend a tankless heater of any kind to anyone.

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Scott Sklar

About: Scott, founder and president of The Stella Group, Ltd., in Washington, DC, is the Chair of the Steering Committee of the Sustainable Energy Coalition and serves... more »