Rinnai On-Demand Water Heater Problems, Issues, Concerns, Limitations




In this piece we look at Rinnai on-demand water heater problems customers sometime see. A Rinnai on-demand water heater offers many real advantages over traditional hot water tank units.  But drawbacks, limitations, and disadvantages exist for them too.

Now to be certain, Rinnai on-demand water heaters can be a great investment in your home’s overall comfort. They offer unlimited, well-heated water for hour-long showers, many daily loads of laundry, and even outdoor hot water uses.  You can de-ice a whole, long driveway, and never run out of hot water.




Please consider the following Rinnai on-demand water heater problems. Factor in these cons, concerns, complaints, and issues before buying. Here’s a pretty comprehensive list.

Rinnai On-Demand Water Heater Problems: High Initial and Ongoing Costs

High Installation Costs

These Rinnai instant hot water, on-demand units indeed offer “fast and endless” hot water.  Plus, they can save you lots on your fuel bill.  But they cost more to buy, install, and maintain. The water heater purchase itself isn’t too costly. Indeed, most on demand units run between $100 and $700. But the specialized wiring for the electric heaters can cost many dollars.  Plus, ventilation for the gas heaters can also set you back big bucks to have installed.

Fuel Savings Estimates May Be Overblown

Yes. When you don’t use much water, keeping tens of gallons in reserve raises your energy bill. This is what happens in a traditional tank-based heater. So you’d save that amount if you switched to an on-demand water heater system.

But this savings may not tally to very much. Why not? Because if you are going away for more than a couple of days, then just turn off the heater tank. True, when you return home, you’d have to wait an hour or more for hot water. But how often would you do that anyway? And, is this small inconvenience worth the much higher maintenance costs of a Rinnai on-demand system?

Seeing a Return on your Rinnai Water Heater Investment can Take Several Years

Claims abound that you can get as much a fifty percent fuel savings with Rinnai on-demand hot water systems. If true, switching to them from the traditional water heater tank COULD be well worth it over time.  This is especially so in communities with well-conditioned (soft) water, where the exchangers in these heaters tend to last longer.

But recovering your money outlay can take as long as 22 years. That would amount to a savings of the cost of replacing two or three traditional tanks.  This assumes that the on-demand unit would last 22 years.

High Maintenance Costs

You not only pay over twice as much up front for on-demand water heaters. But these units need higher maintenance efforts than traditional tank based units. A heat exchanger comprises the heart of the on-demand system. You must replace this every few years. This more or less depends on the condition of your water and the sort of exchanger packaged with the unit.

These heat exchangers can run a couple to several hundred dollars. Noe your need for endless hot water may cancels out these draw-backs.  If not though, we’d avoid on-demand water heaters until prices drop some more.




Rinnai On-Demand Water Heater Problems: Electrical Provisions

Rinnai Electric On-Demand Water Heaters Need High Capacity Wiring

Some of these units draw a hundred amps at 220 volts (over 22 KW). One example is the EcoSmart ECO 27 on-demand electric water heater. This comprises half of the max current allowed in a home with a typical 200 amp electric utility service!

Further, this high current wire is hard to bend, strip, route, and handle.

Besides, many houses have only a 100-amp service from the utility poll in (service drop). So, upgrading to on-demand water heating would mandate a costly service drop upgrade, to 200 amps at least. Therefore, let a pro do it.  Installing the wiring to an on-demand heater is probably best left to an electrician.  But if you are an electrician yourself, this water heater upgrade project could be fun for you.

If Power Fails, so Also does the Rinnai Electric On-Demand Hot Water Heating

True of the electrically powered on-demand systems. Indeed 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 on-demand water heater. Gas fueled units may also require a small amount of electricity from the mains.  This power runs their control systems.  So, even certain gas units would not work during power outages.

Available hot water would flow away almost immediately after turning on a connected hot water faucet. It might be wise thus, to keep a traditional gas water heater tank in the basement.  Leave it connected to the plumbing system through valves, that you could open should you lose electricity.

Less Advantageous Compared to a Big Hot Water Tank.

Further, near constant how water draw situations benefit less from on-demand water heating.  Like where women reside (*smile*). Why? Because drawing enough water, you would actually use the hot water before having to reheat it too many times. We’ll wait until more people experience this technology and see how they feel about it.

Rinnai On-Demand Water Heater Problems: Hot Water Delivery Issues

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 the Rinnai on-demand system, as do the other major brands, needs a minimum water flow to turn on.

The Chilly On-Demand Water Heater Pause

These water heaters do not turn on until they sense actual water flow. Plus, they keep no reservoir of hot water. So, 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 on-demand water heating.

Hot Water Temperature can Vary with  Flow Pressure

Where water pressure to the Rinnai on-demand water heater varies, so too may the hot water temperature.  E.g.  When a toilet is flushed or a washing machine begins to fill.  In these cases, the hot water can become cooler and startling for shower takers.

For absolutely consistent water temperatures, the basic Rinnai on-demand water heaters require near-consistent water pressure. The more common tank-based systems do not suffer this drawback though.

You can reduce this pausing problem by purchasing a more expensive, modulated on-demand water heater however.




Rinnai On-Demand Water Heater Problems: Ongoing Support Hardships

On-Demand Water Heaters, Different from Instant Hot Water.

On-demand hot water systems, contrary to popular belief, do not give you instant hot water, at the tap. Not exactly. They may heat up the water that passes through them instantly. Plus, they do so without any significant water reservoir.  But you still will not see instant at the faucet. Why?

Consider.  Even with one of these on-demand water heaters, you’ll still feel some delay.  Experience shows that you’ll still get that pause between turning on a hot water faucet, and actually receiving hot water.  This is especially true 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.  In that time, the heated water moves through the pipes from the heater to your faucet.  Thus the further your faucet is from the water heater, the less advantage of on-demand heating.  Merely upgrading to on-demand won’t get rid of this hot water delay in these cases.

Add a Pump Circulator for Truly Instant Hot Water

On-demand water heaters do not solve this problem. But, installing a return pipe and a circulating pump on the other hand, does. It gives you instant hot water, without incurring the expense of a tankless system. You need not buy on-demand heaters to get instant hot water therefore.  Plus, the cost of the circulating pump and plumbing may indeed be much less than going tankless.

Water Treatment System Needed for Longest Water Heater Life

Among the Rinnai on-demand water heater problems, mineral buildup.  These systems are sensitive to water impurities and minerals in the water.

But you can prevent buildup of limescale and other hard water deposits.  How?  Install a water softening and filtration system at the cold water side of the Rinnai on-demand water heater.  True, this amounts to more cost for this hot water heater upgrade project.  But your Rinnai on-demand water heater will thank you for it.




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References for Rinnai On-Demand Water Heater Problems

Revision History

  • 2018-06-04: First published.