Main Course: Tankless Water Heaters
By Dan Greenberg, Associate Director, E Source -- Foodservice Equipment & Supplies, 8/1/2008 12:00:00 AM
Tankless water heaters, also known as instantaneous or on-demand water heaters, provide hot water without using a storage tank. Like tank water heaters, tankless water heaters use either gas or electricity to operate. Cold water travels through a pipe into the unit, and either a gas burner or an electric element heats the water. In foodservice operations, tankless water heaters can be supplementary units placed at the point of use or can replace a centralized tank water heater.
Unlike conventional water heaters, tankless water heaters are very efficient because they do not have standby losses incurred by continuous use of energy to maintain water in a tank to a set temperature. They also save space, which can be particularly useful for crowded kitchens, allowing them to use the area for more productive and profitable use.
In addition, tankless water heaters tend to have longer service lives than tank-based water heaters. While foodservice operators must typically replace their tank water heaters every six to 10 years, tankless units are typically designed to last 20 years. Tankless water heaters’ reduced maintenance and replacement costs go a long way toward offsetting the higher purchase price, which can run from $1,000 to about $2,000, depending upon output capacity.
One drawback of tankless water heaters is that although they theoretically provide endless hot water, most units, particularly electric units, provide heat more slowly than conventional tank water heaters. This can slow the performance of flow-dependent equipment such as warewashers. This poses a problem for such places as a full-service restaurant. These foodservice operators can overcome this disadvantage by plumbing multiple tankless units in parallel to provide the desired flow rate. In other applications, the lower flow rates available from tankless heaters are often adequate for the job. Indeed, tankless water heaters are becoming an increasingly popular option for many quick-service restaurants.
The term "energy factor" characterizes the efficiency of both tank and tankless water heaters. The energy factor is the portion of the energy going into the water heater that gets turned into usable hot water under average conditions. It takes into account heat loss through the walls of the tank, up the flue, and in combustion. The higher the energy factor, the more efficient the heater.
Because tankless water heaters don't have the losses associated with tanks, their energy factors are normally higher. Energy factors for gas tankless water heaters typically range from around 0.78 to 0.85, compared with 0.58 to 0.67 for a conventional gas tank and as high as 0.86 for an ultra-efficient gas tank heater. In January 2008, one manufacturer introduced a much higher efficiency gas-fired tankless water heater to the market with an impressive energy factor of 0.98. Although the purchase cost of this unit is higher, its installed cost is reportedly on a par with other tankless units because its low-temperature exhaust can be vented through inexpensive PVC pipe rather than the stainless-steel ductwork needed for other tankless water heaters.
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