Let’s take a look at
tankless water heaters by Jim Johnson
E
MPLOYEES who attend corporate retreats are sometimes
divided into small groups to participate in “team-building” exercises. One such scenario involves a team who must work together to figure out what to do if they were trapped in a basement after an earthquake. One idea for which a team gets points is to remember to isolate the water heater so they’ll have drinking water until they’re rescued. And that’s the basis of the first objection that arises from people in California if tankless water heaters are suggested as an alternative to standard water heaters, which store 30 or 40 gallons … the fear that there wouldn’t be sufficient water in the event of an earthquake. Meanwhile, if your customer isn’t in an earthquake-prone area or if they’ll consider another way to deal with a potential natural disaster, they may consider “going green” with the savings in operating costs that tankless water heaters provide. Available in both gas and electric models from a long list of both domestic and foreign manufacturers, most of today’s units are designed with a sensing system that modulates the flow of water through either the heating elements (electric) or heat exchanger (LP or natural gas models). Figure 1 illustrates a model offered by Takagi Industrial, a manufacturer with headquarters in Irvine, California. This example shows the typical location of the flow sensor on the cold water inlet line that starts the heating process when a hot water tap is opened. The sensor lets the microprocessor know that water is being called for, and in turn, the ignition process, employing a spark ignition system, is accomplished. In addition to a sensor on the cold water inlet line, many gas units employ a second sensor to monitor heat exchanger temperature and a third to monitor the temperature of the water leaving on the supply line to the hot Figure 1 water tap. The overall technology of tankless water heaters isn’t really new. Rheem Manufacturing, for example, has been offering them since 1945 for both residential and commercial applications. Rheem contends that with the technology now available in tankless water heaters (including a modulating gas valve that varies the flame depending on the level of heat required), an endless supply of hot water is available. One comparison they note is an estimate that a 50-gallon, tank-type water heater will run out of hot water after the third consecutive 10-minute shower from a 2.5 GPM shower head, while a tankless model will be able to keep up with
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February 2009
demand for not only those consecutive showers, but beyond. Speaking of showers, some manufacturers of electric tankless units recommend that since most people are comfortable showering somewhere between a temperature of 98°F to 105°F, setting the outlet temperature on a tankless water heater somewhere between 105°F and 110°F will suit their needs. However, when the operating temperature is set within this range, there’s a consideration regarding customer use. Since standard water heaters often operate at a temperature higher than the often tankless outlet temperature, the end user must remember that they will be using