Stock picture of the Rheem RTE 9 electric tankless water heater, front view.

Tankless Water Heater Disadvantages, Cons, Issues

There are many tankless water heater disadvantages to think about before plunging in.  So, use caution before buying tankless.  We discuss most of these issues below.

Stock picture of the EcoSmart ECO 27 electric tankless water heater, front view.
EcoSmart ECO 27 electric tankless water heater, front view, stock photo.

Tankless Water Heater Disadvantages

High Startup Costs

These so-called instant hot water, on demand units indeed offer “fast and endless” hot water.  Plus, they save you on your fuel bill.

But among the many tankless water heater drawbacks, is their higher expense.  For example, they cost more to buy, put in, and keep up.  The heater cost itself isn’t bad though.  Most on demand units cost between $100 and $700.  But the high current wiring for these heaters, or the vent for gas models, cost big bucks to put in.

High Maintenance Costs

Among the tankless water heater disadvantages is this. Not only do you pay over twice as much initially for them. But they need higher maintenance effort than traditional units. Why?  Because you must replace the heat exchanger in tankless heaters every few years. More perhaps, or less often, based on your water condition.  Harder water usually means shorter life for these exchangers.  Now the heat exchanger can run a couple to several hundred dollars. So unless your need for endless hot water balances these draw-backs, avoid them until their price drops more.

Stock picture of the EcoSmart ECO 27 electric tankless water heater, inside view, with front panel removed.
EcoSmart ECO 27 electric tankless water heater, inside view, with front panel removed, stock photo.

Tankless Water Heater Disadvantages: The Dreaded Tankless Water Heater Delay

This hot water delay happens due to the following factors.  These water heaters do not turn on until they sense actual water flow.  Plus, they hold no hot water in reserve.  Further, there is a slight delay between the time they detect water flow, and when the heaters kick on.  This delay may only be a second or two.  But folks often say that it is still a drawback of no-tank water heating.  All of these add to the to the dreaded tankless hot water delay.

Electric Tankless Water Heaters Need High Current Wiring

Another of the tankless water heater issues, is that some units draw a hundred amps at 220 volts.  In terms of power, this is over 22 KW.  For example, the EcoSmart ECO 27 tankless electric water heater shown above draws at least this.  This power draw is half of max current in 200 amp home service.  This this wire is hard to bend, strip, route, and to handle on the whole.

Further, many houses have only a 100-amp service from the utility poll in (service drop).  Thus, switching to tankless also mandates a service drop upgrade as well.  Leave putting in the wiring for a tankless heater to a qualified electrician.  Do this yourself, only if you work as an electrician yourself.

Stock picture of the Eccotemp FVI-12-LP high capacity propane tankless water heater, front view.
Eccotemp FVI-12-LP high capacity propane tankless water heater, front view, stock photo.

If Power Fails, So Does Tankless Hot Water

True of the powered tankless water systems, since no reserve tank of pre heated water exists in this heater type.  Further, most residential generators do not produce enough emergency power to run a tankless water heater.  Gas fueled units may also need some mains power to run their control systems. So, even these gas units would not work in power failures.  Available hot water would go away almost right away after opening a hot water faucet.  For this reason, keep a gas water heater tank in the basement. Connect it to your pipe system through valves. Then,  you could switch it in if you lose power.

Tankless Water Heater Disadvantages: Getting Back 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 getting back your investment can take as long as 22 years. That would save of the cost of replacing two or three traditional tanks. We assume here that the tankless unit would last 22 years.

Stock picture of the Stiebel Eltron Tempra 24 Plus electric whole house water heater, front view.
Stiebel Eltron Tempra 24 Plus electric on-demand whole house water heater, front view, stock photo.

Tankless Water Heater Disadvantages: Different from Instant Hot Water

Tankless hot water systems, contrary to common belief, do not give you instant hot water.  Of the tankless water heater problems discussed so far, this one can sadden the buyer the most.  Yes, they do heat the water instantly once they come on, and do so without any water reservoir. Yet you still will not see instant hot water at the faucet.  Why?

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.  It takes that long for the heated water to travel through the pipes from heater to faucet.  On-demand water heaters do not solve this problem. But putting in a return pipe and pump  gives instant hot water, without incurring the expense of a tankless system.

In tankless, there’s also a delay in hot water of one to three seconds. You get this  even when right at the heater. This delay happens because it takes the tankless unit some time to sense water flow starts.  So, it does not turn on its heaters right away.  But this delay is no big deal in non point-of-use installations. Where the water flows  down long, cold pipes to sinks, washers, or bathtubs, we expect some delay.  These water travel time delays mask well the turn-on delay at the tankless heater itself. So whatever pause the tankless unit adds has little downside.

Stock picture of the Eccotemp FVI-12-NG high capacity natural gas tankless water heater, front view.
Eccotemp FVI-12-NG high capacity natural gas tankless water heater, front view, stock photo.

Output Water Temp Can Vary with Water Pressure

This, among the tankless water heater cons, surprised us a bit.  Where water pressure to the heater may vary, so can how hot the water is can vary as well.  This happens for example, when you flush a toilet, or a washing machine starts filling.  These water pressure changes can cause the output hot water to go cold and uncomfortable in the shower.  Thus, for constant water temps, tankless water heaters need near-constant water pressure.

Tank-based systems though, do not suffer this drawback.  In fact, you can solve this problem by buying a pricier, modulated tankless heater.

No Hot Water when Flow is a Trickle

You can’t draw just a trickle stream of hot water from your faucets.  Why not?  Because these on-demand tankless systems need a minimum water flow through it.  If the flow is less than that, then they do not sense the flow.  So, the heaters do not come on. Thus, you get only cold water from the hot tap.

Tankless Water Heater Disadvantages: Fuel Savings May Be Less Than you Hope

Yes, when you don’t use much water, keeping tens of gallons in reserve wastes fuel and money.  Indeed, incurring the cost of keeping the tank hot can cost you much.  This is what happens in a tank-based heater. So you’d save that amount if you went tankless.

But this savings may not tally to very much.  Why not?  Because if you are going away for a couple days, just turn off the tank heater.   True, when you get home, you’d wait an hour or more for hot water. But how often would you do that?  And, is this small pain in the but worth the much higher costs to maintain the tankless system?

Further, in places where there’s a near-constant draw of hot water (like where women reside (*smile*), tankless has less benefit.  The advantage of tankless seems less pronounced in this case.  Why?  Because you would actually use the hot water before reheating it too many times with a tank heater. We’ll wait for more people experience the tankless  technology to see how tankless pans out.

Stock picture of the Atmor AT-910-27TP 27 kW / 240v ThermoPro series digital thermostatic on-demand electric water heater, front view, stock photo.
Atmor AT-910-27TP 27 kW / 240v ThermoPro series digital thermostatic on-demand electric water heater, front view, stock photo.
We heat our well water with gas. but will not be buying tankless any time soon. In fact, we hope not to have to buy ANY type of water heater any time soon. Why?  Because we just installed a decent high-capacity tank  several years back. So far, it is working well.

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References for Tankless Water Heater Disadvantages

  1. Advantages and Disadvantages of Tankless Water Heaters  from Best Plumbers
  2. Tankless Hot Water Heaters, the Downside   from Mortgage News Daily
  3. Pros and Cons of Tankless Water Heaters   from Water Heater Rescue
  4. What is a Tankless Water Heater?    on Wikipedia
  5. Where to Buy a   Tankless Water Heater

Suggested Reading

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  2. Thermos Water Bottle Review, Vacuum Insulated Hydration Flask
  3. Electric Baseboard Heater Noise, How to Fix

Post Revisions

  • 2018-04-20: Updated content for better keyword targeting.
  • 2018-03-08: Updated the content and title.
  • 2017-02-10: Revised the tags list. Added pics.  Lengthened the References section.
  • 2015-12-12: Added tags.
  • 2015-01-10: Added the “dreaded pause” problem.
  • 2014-11-11: Added a References section.  Fixed some typos. Added a few more drawbacks to tankless water heaters.
  • 2012-08-14: Originally posted.
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