"Water heater-- should I go tankless"
Column #834 02/19/2011
On The Level
Q. I live in a community that is all electric (no gas). I have a 13 year old electric water heater. It is working fine, but I realize that I'm on borrowed time. I am interested in replacing the existing water heater with a tankless, or on-demand heater. What are your thoughts on these "new" water heaters? I do already have a 100 gallon propane tank for my gas fireplace. Therefore a gas tankless heater could be an option. I realize that the on-demand water heater will have a much higher initial cost. My limited research seems to look like about $2,000 versus only $300 for a traditional electric water heater. I've seen that they have some electric on-demand heaters. However, I've heard that the electric ones are sometimes slow to heat water for an entire house.
A. It’s true the actuarial tables rate water heater life at seven to 12 years working life but if you are on a good water supply that is not acidic water heaters can last quite a while. When I see them over age 20 I recommend they be replaced to be on the safe side. You probably have a few good years to decide what you want to do.
Tankless on demand water heaters have been around for a long time in this country-- their greatest use is in Europe-- but are beginning to get more attention of late here in the U.S. I am beginning to see them more frequently when I inspect newer, high end houses and you are right-- the reason is cost. The numbers you quote don’t sound like installed prices to me but the basic cost of the units. Add labor of installation and the numbers climb appreciably. Electric models are available but gas is really the only way to go, in my book.
Are they more efficient than the old fashioned tank-type water heaters? You bet, but only in a narrow sense. You see, tankless water heating appliances are called “on-demand” water heaters and, as the name suggests, only heat water when you call for it and only heat water that you use. Sounds neat and tidy.
But a unit of energy is a unit of energy and to elevate the temperature of a given amount water from say the 55ºF it is as it comes into the house to 120ºF for hot water use will take exactly the same amount of energy whether it’s in your tankless unit or taken from the big old round, five foot tall water heater in the basement. The difference is the older water heater technology heats water up slowly and stores it for use in a vessel much like a big thermos bottle. The tankless unit uses a great amount of energy all at once to rocket the temperature up for your use. The energy needed to keep the stand-by water in the tank at temperature until you need it is considered wasted by those who calculate such things. More about that in a minute.
If you have gas available then a gas unit is what you want. Electric models require a huge amount of power to operate them and if your house is older you may even need a “heavy-up” of your electrical capacity at the main panel box to supply the added draw. In today’s dollars that can run $1,200. and up. Also the location of the on-demand water heater relative to the electrical main panel box comes into play as very heavy cable will have to be used to wire it. If it’s gas you need to position it on an outside wall so the flue gasses can vent out of the house.
My experience is that the manufacturers of these tankless heaters are optimistic about their output rates of hot water. Your needs might be calculated at 2.5 gallons of water at 120ºF. per minute. If so, then I would recommend that you up-size the unit one magnitude of output greater to be sure.
Tankless water heating that most folks see overseas are not only on-demand but also are point of use; that is, they hang on the wall above the sink or tub. Most American families run 26 to 29 gallons of water a day down the drain at sinks, showers and tubs waiting for hot water. So if you use a central tankless water heater you should think about the hot water you are going to let cool in the pipes when you’re done and the jolt of power that it took to heat it in the first place. Traditional water heater jackets are getting much better and the heat leakage tends to be from the conductive metals of the pipes going in and out of them.
If your interest is in thrift and you squared all the costs associated with the buying, installing and operating a tankless water heater against the cost to buy, install and use a conventional tank-type water heater, you’d soon see that any break-even point and savings would probably exceed your lifespan. If your interest is along the lines of thinking globally but acting locally, you’d be better off putting solar panels on the roof and running that heated water into the cold water side of your conventional tank type water heater. But tankless is here to stay and I know those who have them swear by them. And they look way cool.
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