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Lately many homeowners are inquiring with us about “tankless” or “on demand” water heaters. Often touted as a modern, cost-saving alternative, instantaneous heaters haven’t lived up to the hype. There are also some serious considerations to make before purchasing one. Here are the things you don’t hear.
Component failure resulting from water quality issues is not covered under the product warranty.
Evaluation of your water quality is a must! If the water quality exceeds the target levels provided in the following table, the manufacturer may not honor the warranty. There have been excessive warranty claims on most brands of tankless heaters due to heat exchanger problems. Most are due to inadequate water quality and lack of maintenance, which I will explain further in a moment.
Here’s the table:
Maximum Level
Total Hardness Up to 200 mg / L
Aluminum * Up to 0.2 mg / L
Chlorides * Up to 250 mg / L
Copper * Up to 1.0 mg / L
Iron * Up to 0.3 mg / L
Manganese * Up to 0.05 mg / L
pH * 6.5 to 8.5
TDS (Total Dissolved
Solids) *
Up to 500 mg / L
Zinc * Up to 5 mg / L
*• Source: Part 143 National Secondary Drinking Water Regulations
Some of the wholesale distributors will not even sell tankless heaters because of the amount of problems they have encountered.
In addition to their high purchase price, instantaneous heaters require a separate fuel connection, electrical circuit and exhaust venting. They will frequently require relocating the heater as well which drives the cost even higher.
Performance is also limited by the heater’s ability to keep up with demand. Because they have no reserve storage, running more than one fixture at a time can push some instantaneous heaters to their limit.
Here in the Northeast our groundwater is colder in the winter months. Tankless heaters have a temperature sensor which limits water flow to the amout the heater can keep up with heating, resulting in slower water flow in colder months.
One of the most important, and most overlooked, factors with a tankless water heater is
annual maintenance.
The manufacturers recommend multiple chemical flushings of the heat exchanger to prevent corrosion, liming and mineral deposits. This is most likely something you will need to have your serviceman do, which should cost between $200 and $300. Annually!
Finally, in homes with high usage, efficiency is typically no more than 8-14% better than with old-fashioned tank-type heaters, meaning it can take over 20 years to achieve payback.
Maybe tankless heaters are not all their cracked up to be? You be the judge.
