While whole-house has its advantages, as far as cost and complexity, it may take a minute or more to get hot water to a sink, dishwasher or other distant fixture, wasting both water and energy.
Point-of-use setups heat water at the faucet or other fixture. Point-of-use water-heating can be by either a tank or an on-demand system.
Q: Is on-demand water-heating a new technology?
A: On-demand water heaters have been popular in Europe and Asia for decades. They have not caught on here because they cost twice as much to buy as conventional tanks, and there are additional installation costs for retrofits.
But they last longer since mineral deposits, rust and corrosion are all but eliminated when hot water is not stored, and in general the parts are of higher quality.
Q: Why all the interest now?
A: Two reasons: The $300 federal tax credit (credit, not deduction) that went into effect Jan. 1, and the spike in energy prices.
Any water heater with an "Energy Factor" (U.S. government efficiency rating) of greater than .8 is eligible for the tax credit. The best tank-type water heaters max out at .6, while the on-demand units start at .8 and go up. Real world energy savings could be from 20-35 percent, depending on your usage patterns. As prices of energy go up, so go your savings.
Q: What are other advantages of this water-heating system?
A: An endless supply of hot water is one very nice advantage. It heats as it goes; no supply of hot water to deplete. Also, a typical instant water heater is about the size of a suitcase and can mount on a wall or in a crawlspace.
Q: What are the disadvantages?
A: We are pretty much limited to gas or propane for whole-house systems. Our water is too cold in the winter to be practical for electrical systems.
With 40-degree incoming winter water temperature, barely enough hot water for a shower is supplied on an electric setup. In the summer, you will get enough for one shower and one sink. Of course, this is with three 240-volt, 40-amp circuits running full tilt to get there. That is some serious juice!
A large percentage of homes don't have that capacity. For that electric heater, you need a minimum of 200-amp service to the house. Even when so equipped, this takes a lot of wiring work. This expense is too much for a system that most would consider inferior anyway.
There's also the issue of power outages. With any on-demand system, you have only cold water when the power goes out. With a conventional tank, you should have at least enough hot water in reserve to finish your shower in comfort.
Darrell Hay is a local home inspector and manages several rental properties. |
