There are many tankless water heater disadvantages to think about before plunging in. So, use caution before deciding to buy one. We discuss most of these below.
Tankless Water Heater Disadvantages
High Startup Costs
While these so-called instant hot water, on demand units indeed offer “fast and endless” hot water, and do save you significantly on your fuel bill, they cost more to purchase, install, and to maintain. The heater purchase itself isn’t too bad, with most on demand units costing between $100 and $700. But the specialized wiring for the electric heaters, and the ventilation for the gas units can run into some big bucks to have installed.
High Maintenance Costs
Among the tankless water heater disadvantages is that not only do you pay over twice as much initially for them, but they’re higher maintenance than traditional units. They have a heat exchanger that must be replaced every few years (more or less depending on the condition of your water and the sort of exchanger packaged with the unit), and that can run a couple to several hundred dollars. So unless your need for endless hot water balances these draw-backs of the tankless models, I’d avoid them until their price comes down a little more.
The dreaded tankless water heater pause
Since these water heaters do not activate until they sense actual water flow within, they do not keep any reservoir of hot water. Plus, there is a slight delay between the time they detect water flow, and when the heaters actually kick on. This delay may only be a second or two, but folks often site it as a drawback of no-tank water heating.
Electric Tankless Water Heaters Require Very High Current Wiring
Some of these units can draw a hundred amps at 220 volts (over 22 KW, as does the EcoSmart ECO 27 on demand electric water heater pictured above); which is half of the maximum current allowed in a home with a typical 200 amp electric utility service. This type of wire is difficult to bend, strip, route, and generally, to handle. Further, many houses have only a 100-amp service from the utility poll in (service drop). Thus, upgrading to tankless would also mandate a service drop upgrade as well, to 200 amps at least. So installing the wiring to a tankless heater is probably best left to an electrician, unless of course, you are an electrician yourself.
If Power Fails, So Also Does the Tankless Hot Water
True of the electrically powered tankless systems, since no reserve tank of pre heated water exists in this type of heating. Further, most residential generators do not produce enough emergency power to run a tankless water heater. Gas fueled units may also require a small amount of electricity from the mains to run their control systems, and so, even certain gas units would not function during power outages. Available hot water would disappear almost immediately after turning on a connected hot water faucet. For this reason, it might be wise to keep a traditional gas water heater tank in the basement, connected to the plumbing system through valves, that you could engage when electricity is lost.
Recovering Investment Takes Many Years
Claims abound that you can get as much a fifty percent fuel savings with these continuous flow hot water systems. If true, switching to them from the traditional water heater tank COULD be worth it over time; especially in communities with well-conditioned (soft) water, where the exchangers would tend to last longer. But recovering your investment can take as long as 22 years. That would amount to a savings of the cost of replacing two or three traditional tanks, assuming that the tankless unit would last 22 years.
Tankless Water Heaters, Different from Instant Hot Water
Tankless hot water systems, contrary to popular belief, do not give you instant hot water. While they may heat up the water that passes through them instantly and do so without any significant water reservoir, you still will not see instant at the faucet. Why? Consider that even with one of these inline water heaters, experience shows that you’ll still get that pause between turning on a hot water faucet, and actually receiving hot water; especially if the place where you’re drawing the hot water is far away from the water heater. You still must wait through the coldness for several seconds to a minute, for the heated water to travel through the pipes from the heater to your faucet. On-demand water heaters do not solve this problem. Installing a return pipe and a circulating pump on the other hand, will give you instant hot water, without incurring the expense of a tankless system. There’s also a brief delay of hot water output of one to three seconds, even if sampled right at the heater, because it takes the unit a bit of time to sense when water flow has begun, and this, to activate the heating elements. However, this delay is probably insignificant in non point-of-use and centralized installations, where the hot water must travel some distance down cold pipes before reaching the sink, washer, or bathtub where it will be used.
Output Water Temperature Can Vary with Water Pressure
In situations where water pressure input to the heater may vary, such as when a toilet is flushed or a washing machine begins to fill, output water can become cooler and startlingly uncomfortable for shower takers. For absolutely consistent water temperatures, tankless water heaters require near-consistent water pressure. More traditional tank-based systems do not suffer this drawback. This problem can be minimized by purchasing a more expensive, modulated tankless heater however.
No Hot Water when Flow is a Trickle
You can’t draw just a trickle stream of hot water from your faucets, since the on-demand tankless system requires a certain minimum amount of water flowing through it, in order for it to sense the water flowing, and then activates its heaters.
Fuel Savings Estimates May Be Exaggerated
Yes, when you don’t use much water, keeping tens of gallons in reserve, and incurring the cost of keeping it hot, as is what happens in a traditional tank-based heater, costs some money. So you’d save that amount if you went tankless. But this savings may not tally to very much. Why not? Because if you’re really concerned, and are planning a trip away from home for more than a couple of days, you can just turn off the traditional heater tank until you get back. True, when you return home, you’d have to wait an hour or more for hot water. But how often would you be doing that anyway, and is this small inconvenience worth the much higher maintenance costs of the tankless system? Further, in places where there’s a near-constant draw of hot water (like where women reside (*smile*), the advantage of tankless seems less pronounced, as you would actually be using the hot water before having to reheat it too many times with a traditional water heater. We’ll have to wait until more people have experience with this new technology and see how it pans out.
- Advantages and Disadvantages of Tankless Water Heaters from Best Plumbers
- Tankless Hot Water Heaters, the Downside from Mortgage News Daily
- Pros and Cons of Tankless Water Heaters from Water Heater Rescue
- What is a Tankless Water Heater? on Wikipedia
- Where to Buy a Tankless Water Heater
- 2018-03-08: Updated the content and title.
- 2017-02-10: Revised the tags list. Added pictures. Extended the References section.
- 2015-12-12: Added appropriate tags.
- 2015-01-10: Added the “dreaded pause” disadvantage.
- 2014-11-11: Added a References section. Fixed some typos. Added a few more drawbacks to tankless installations.
- 2012-08-14: Originally published this article.