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ASK THE CARPENTER

Tips for selecting a tankless hot water heater

Q. I’m writing about your Oct. 30 column about water heaters (“When to replace your hot-water tank”). We have a natural gas-powered vent-tank unit in the basement of our condo that is eight years old. We are experiencing no problems, but I would like to explore the on-demand alternative and noticed your preference for those units. I have not found much current information about on-demand water heaters on the Web, so I would like to know why you prefer them. Do you think the avoidance of a catastrophic failure is an important consideration? I’d also appreciate it if you passed along the contact information for plumbers who have experience installing these units.

ED KOFRON

A. Hi, I’m sorry, but I cannot recommend service professionals in my column. I suggest that you go to a plumbing supply store and ask for referrals.

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I think catastrophic failure could happen with any unit, so I would not swap yours out for only that reason.

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A tankless on-demand heater can be a great solution to your residential hot-water needs. These types of hot-water heaters do not store water; there is no storage tank or the subsequent heat loss that comes with having one. They provide a continuous supply of hot water via energy-efficient and space-saving, self-contained high-powered burners, but they can be costly to install.

I like this option because you’re not wasting energy, fuel, or money on heated water while you’re sleeping, at work, or on vacation. Installing one of these units is “green.”

TIP: To avoid disappointment, make sure to size the unit correctly based on your water usage. The size and number of whole-house tankless water heaters you’ll need will largely be driven by the flow rate, and that is determined by the number and types of fixtures you may have running at one time. My unit can handle only one shower and one faucet or the dishwasher at one time.

Q. Seven years ago I transferred from oil heat to gas and had a high-end boiler with a 40-gallon hot-water tank installed. I have a Cape Cod-style house with a half bath on the first floor and a full on the second.

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There is a constant problem regulating the water temperature while taking a shower in the second-floor bath. After setting the initial temperature, the water fluctuates to cold quickly as if it were running out of hot water (in under a minute). It constantly calls for a higher temperature until the lever is turned all the way, and then you run out of hot water. The first-floor bath does not have this problem.

When I first complained, the heating company installed a new diverter. No luck. They came back and raised the temperature to about 130-degrees Fahrenheit, but we are still having the same problem.

I called another company, which put a thermometer in the water while it was running. They noticed that the temperature was fluctuating, too, but were at a loss as to how to fix it.

I would like to have the long, hot shower I was promised. Any thoughts?

JOE PICANO, Wakefield

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A. This has been happening for seven years? Is it possible that you have had a defective unit from Day 1? Is this happening anywhere else in the house? Did the plumber check you shower valve? I suggest you check your warranty and call the manufacturer for advice.

Rob Robillard is a general contractor, carpenter, editor of AConcordCarpenter.com, and principal of a carpentry and renovation business. Send your questions to homerepair@globe.com or tweet them to @robertrobillard.