Recently a reader asked if we thought installing an on-demand, or tankless, water heater was smart. We responded "Yes, in theory."
Conceptually, heating water as it’s needed makes more sense than heating water and storing it in a tank for later use. We ended that column with the statement that the tankless models theoretically are a reasonable alternative, but with a caveat to do your homework.
Of course, the devil is in the details, and once again our readers offered their opinions and experience. Several pointed out potential trouble spots. The flaws they identified ranged from higher operating costs to retrofitting gas lines to situations in which the things just don’t work.
One reader writes:
"I had to respond to your rave review of on-demand water heaters. My landlord put them in our building (a fourplex) about six weeks ago, and I truly hate the results. Often the wait for hot water to come out of the tap is as long as two minutes (I’ve timed it), with the faucet on at full strength. I lived in France for a time, and those water heaters never worked properly in the apartments I lived in there, but I thought perhaps there had been some innovations in the tankless heaters here. In a word, no. I would never recommend them for anyone."
In response, we’d hardly say we gave a "rave review," only that tankless water heaters made sense and that the jury was out. Two minutes for "on demand" hot water is unacceptable. We wonder if there may be some problem with the design of the system or the installation or location of the heaters.
This reader likes her tankless model, but it needs some tweaking. She writes:
"We had a tankless installed about two years ago. It works great. Our problem is that the heater is a long way from the two bathrooms and kitchen, so we have to wait a long time for hot water, and we waste a lot of water, which bothers me. At the time we got the tankless, we had all our pipes replaced, and we had to make a decision on where to put the heater.
"Our bathrooms are at opposite ends of the house, the kitchen is in between and the gas service is near none of them. So we put the heater where the gas service comes into the house to save running more gas pipe, and because there was a good place for it in the crawl space.
"I’ve seen some articles about instant hot water pumps that go under a sink. Would one of these pumps help our situation?"
An auxiliary pump reheats the water closer to the point of delivery. It’s worth looking into. …CONTINUED
Another reader pointed out what may be the root of this problem: undersized gas lines:
"The location of the heater with respect to the gas meter is of importance. Since the on-demand heater requires great quantities of gas for a short time, the supply line to the heater may have to be increased to prevent an excessive pressure drop. This is another case of location, location, location."
Which brings us to cost. The reasons to replace a conventional heater with a tankless model are water and energy savings and, ultimately, reduced cost of operation. Repiping the gas lines is an added cost of installation that could make going tankless cost-prohibitive.
One reader did the math. He is not convinced that tankless water heaters are cost-efficient. He writes:
"I did a quick-and-dirty calculation of the annual cost of such a heater versus a hot water tank in our house, and it worked out to being about twice as expensive as a conventional system, even while ignoring the cost of retrofitting the water and gas lines and the venting. We live in San Francisco and will be due for a new water heater very soon, but I think the units will have to come down in price substantially to compete with the more conventional technology."
And finally, a reader made this point:
"There are a couple of issues you failed to address. Foremost is that tankless heaters are very inefficient at low flow rates, requiring a certain amount of water to be passing through the system before it is activated. This makes it impractical for low-flow applications such as rinsing dishes when cold water is added to the mix. For the most part, the heater will shut down because of not enough water passing through it, thereby resulting in the user experiencing cold water instead of warm."
So there you have it. Although going tankless is conceptually a good idea, it may be that it’s more suited for a new installation where all the engineering is in place, rather than a retrofit.
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