JAMES AND MORRIS CAREY | ON THE HOUSE In some places, heating water is a tankless job

We have a favorite Italian deli in our neighborhood. Due to its popularity, everyone must take a number for service.
Waiting in line from time to time for a sandwich is acceptable. However, drawing numbers at home to determine who gets to shower first is not. Yet, such is a daily routine in many American homes due to the hot-water supply. The problem worsens as a family grows and there are more showers to take, clothes to launder and dishes to wash.
In most American homes, hot water is generated in a tank-type, gas-fired water heater. It is like a large thermos with a burner at the base. Cold water enters the top of the tank and is delivered near the bottom through a small plastic pipe called a dip tube. A thermostat measures the temperature of the water and activates the burner to heat the water to the desired temperature. When the demand exceeds the supply, a cold shower is the result. It's abated only once the water heater has had time to heat a fresh tank of water -- usually several minutes. The problem is worse in winter, when the ground water is colder and the water heater works harder to raise the water temperature.
There's another factor that affects the efficiency of a tank-style water heater -- sediment. Over time, sediment (hard water deposits, calcium carbonate, etc.) accumulates at the base of the tank; this reduces the effectiveness of the burners and curbs energy efficiency. Innovations in tank-type water heaters, such as curved dip tubes that are designed to prevent sediment from collecting, have helped the problem. However, for maximum efficiency, all tank-type water heaters should be flushed periodically.
New product
Though tank-type water heaters have been the standard in America for decades, there is a new kid on the block -- the tankless water heater. It has been widely used in other parts of the world, most notably Europe and Japan, where energy resources are more precious than in the United States.
As its name suggests, a tankless water heater has no holding tank. Instead, it heats water instantaneously, as it is needed, in a fin-tube heat exchanger. Since no storage tank exists, there is no standby energy loss associated with the storage of hot water; there is no standing pilot and no sediment buildup to deal with.
When you open the tap, the tankless water heater senses the flow, and the electronic ignition starts the water heating process. The water flows through the heat exchanger and is heated to the temperature you choose. Then, the hot water is delivered to the taps in your home that are open.
Most tankless water heaters are microprocessor controlled and use feedback from a water-flow sensor to adjust the burner, which delivers a consistent water temperature. This is an important feature if you have small children or elderly people in your home. When the tap is closed, the tankless water heater shuts off.
Flow rate
A tankless water heater provides continuous hot water and never runs out. However, the volume of hot water -- measured in gallons per minute of flow (gpm), or "flow rate" -- provided by this style of heater is affected by several factors.
First is the size of the burner. The bigger the burner, the greater the flow rate. For example, a tankless water heater with a Btu input of 175,000 can produce up to 6.3 gallons per minute, which is enough hot water to take three simultaneous showers in summer (where the ground water supply is at least 68 F). Conversely, a unit with a Btu input of 380,000 can have a flow rate of up to 13.2 gallons per minute; enough to take six concurrent showers where the ground water supply is at least 68 F.
Chances are you won't be taking six showers at the same time, but, if your home is like most, simultaneous showering, clothes laundering and dishwashing is likely. The flow rate for most of these units is designed to allow all these activities to occur simultaneously.
Looks, cost
If you haven't seen a tankless water heater, you're in for a surprise. It looks nothing like a conventional tank-type water heater.
Though size varies, the average is about 24 inches high, 18 inches wide and nine inches deep -- taking up a little more than two cubic feet. They are wall-mounted, and unlike conventional tank-type water heaters, can be mounted both indoors and outdoors. An electronic controller allows for easy temperature adjustment.
Plan to spend several times what you would shell out for a tank-type unit; tankless water heaters cost from $500 to about $2,000 for the average residential unit. Most units come with a 10-year warranty, and industry estimates indicate that tankless units can save up to 46 percent on water heating costs. That number, based on the increasing cost of energy, can represent big savings. Thus, the higher purchase price usually can be recouped after just a few years of use.
In earlier days, we were cautious -- even opposed to -- tankless water heaters, but with improved technology, we now give them two thumbs up.
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