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Re: Tankless Hot Water Heaters: Are They Worth the Price?

From: RMB007@bellsouth.net
Category: Other/Misc
Remote Name: 67.34.131.40
Date: 21 Feb 2006
Time: 06:29 PM

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Question: Are tankless water heaters worth the premium price and are they able to provide sufficient hot water for the average family?

Builders Websource® Answer: An in-depth discussion of tankless water heaters (also called on demand water heaters) is available in the Builders Websource technote section. However, to answer your specific questions, we're providing additional information here.

Tankless heaters have been popular in Europe and Asia for decades. Their popularity is rising rapidly in the US and some predict that within the next few years, a majority of new homes will use tankless water heaters. Japanese manufacturers such as Takagi, Rinnai, and others represent the lion's share of the market, including products they OEM to US manufacturers (which are scrambling to catch up while protecting their existing tank-heater revenue streams). While electric units are best for point-of-use heating or low demand (or in locations where gas is unavailable), a properly sized tankless gas water heater unit can supply much higher flow rates to provide ample hot water to a typical family. However,  high-capacity units often require 200,000 BTU or more, which can tax many existing gas supply lines. As a result, if you haven't plumbed for this high demand at the outset, you could find yourself needing to run a dedicated line from the gas regulator to the water heater to avoid starving other appliances or the heater itself.

However, the advantages of on demand water heaters can be compelling, including the small space required to install them, resistance to seismic capsizing, energy efficiency (you only heat the water you use), and the virtual continuous supply of hot water -- ideal for filling large whirlpool tubs.

Keep in mind, though, that on-demand water heaters and "instant" hot water are two different things. There will always be a thermal lag based on the distance between the tap and the water heater. Unless you install a more complex recirculating system,  you'll need to allow the water to reach the tap before it will be hot. In this sense, there's no difference between a tank heater and a tankless water heater.

However, since the tankless heater can often be installed in a more central location (due to its small size), you can often place it closer to the faucets. Alternatively, in a very large home, you might consider more than one heater, zoned according to the required supply and distance to the taps.

The required temperature rise to a desired preset temperature will affect the ultimate flow rate. For example, if the ground water is 55 degrees and the target temperature is 120 degrees, this represents a thermal rise of 65 degrees. Depending on the efficiency and BTU capacity, some units could supply as much as 5-8 gallons/minute of hot water. However, if the incoming water temperature is 45 degrees (such as in the winter), the effective flow rate will be reduced in order to achieve the same output temperature. Sizing the heater is critical to ensuring an adequate supply of hot water under peak demand. Consult the manufacturer's instructions and design guide prior to selecting a model.

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