A hot issue keeps boiling over in the plumbing department: tankless hot water heaters.
These devices, which can fit in a closet and eliminate the need for a bulky hot water tank, reputedly can save a homeowner hundreds of dollars a year in electricity, natural gas or propane by heating the water “on demand” as it passes through the tank.
According to the U.S. Department of Energy, tankless water heaters eliminate standby heat losses from heating a tank of water and letting it sit there all day keeping the dog warm as the heat slowly escapes.
But the question is, do they really work?
There are passionate arguments on both sides, with true believers claiming they are the best thing since peanut butter and banana sandwiches, and others breaking into tears every time they pay their heating bills.
Tankless hot water heaters have been in use in Europe and Japan for a long time – places where apartments are so small a 24- by 60-inch hot water tank sticks out like the Eiffel Tower. Such abodes usually don’t house a family the size of a barbarian horde, and a quick shower is all that’s needed to get the day going. But put an on-demand water heater in a typical American family home, and cries of anguish begin to be heard throughout the land.
For homes that use about 40 gallons of hot water a day, tankless appliances are often adequate. But for a full-size family that may have the shower, the washing machine and the kitchen sink all going at the same time, the equation quickly changes.
The output of most tankless water heaters is only 2 to 3 gallons of water a minute, according to Walton EMC, a Georgia electricity cooperative. That’s about the rate of a single shower. This means you can do only one thing at a time with a tankless unit. Whether to shower or wash the dishes can involve a conclave for most families. By the time a choice is made, that 65-gallon traditional tank in the corner would be all warm and cozy for use by everyone.
Since tankless water heaters don’t have standby heat losses, their energy factor is a high 0.98, Walton says. But superinsulated water heaters come close, at 0.91. Even if you keep the temperature at a relatively low 120 degrees, the storage tank can be more competitive energy-wise.
That’s because a tankless heater has to fry up a whole lot of BTUs to heat any amount if water. Imagine having to rewire your entire electrical system to get enough juice to power an electric on-demand tank, or installing a bigger propane tank. With natural gas, of course, you just pay the bill.
And heat loss from a traditional hot water tank helps heat the home as well as the dog. A tankless heater may actually increase heating costs, according to the Star-Tribune in Minneapolis. Furthermore, much-touted gas-fired tankless heaters often require larger venting than a traditional tank, which means tearing a bigger hole in the roof. That’s not cheap.
What’s the solution for skeptics and die-hards? Simply install an on-demand unit at every hot-water outlet, the manufacturers recommend.
At $1,000 or so a pop, plus the energy costs of each heating unit, it may be cheaper to install an industrial steam boiler in the basement.
The claim of “instant” hot water also may be more myth than prophecy.
Chili Pepper Appliance, which sells pump units online, admits that tankless heaters can actually increase water wastage since you may have to let the faucet run longer to get that uninterruptible supply of hot water.
After all, a tankless unit has to fire up and blaze away for a bit to warm anything, and then that hot water has to make its way to the tap. Not exactly instantaneous.
There’s much to be said for a tankless water heater installed in the right place. But doing a little arithmetic is a good idea before making the choice.
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