We recently had a Rinnai water heater installed at our home–at a cost of $2,600 (considerably more than a conventional water heater). It’s a tankless heater, which means that instead of constantly keeping a tank of hot water at the ready, it virtually instantaneously heats water when a request for hot water is made.
The principle is a great one and Marysia is quite familiar with their use in Poland where, as in much of Europe, they are quite common. They conserve one’s use of natural gas as the gas only runs on demand. It doesn’t needless heat hot water when hot water is not being used. They’re so green that they qualify for a $300 tax credit.
It all sounds great, right? So, what’s the problem? Well sir, the reason these heaters are possibly crap is their minimum water-flow rate. As the Rinnai FAQ puts it:
20. What is the minimum water flow rate required to operate a Rinnai?
The Rinnai tankless water heater must be able to sense water flow in order to initiate operation. Most Rinnai models will operate with flow rates as low as 0.5 gallons per minute. [Our unit is officially rated for 0.6 gallons per minute.] This is the lowest minimum flow rate in the industry and is an important benefit.
In practice, however, the flow rate in my shower frequently runs below this minimum. Consequently, the heat turns off after about two minutes of showering–and that’s with the hot water tap turned fully on. The problem is my low-flow shower head. By restricting the water flow, it takes me below the minimum the Rinnai requires.
In my wife’s, Marysia’s, bathroom, the shower head is more powerful and she doesn’t run into this issue as often, but when she takes more extended showers she has lost heat.
We asked the plumbers (Hicks) who installed it and the dealer who sold it to us (Central Supply) about this issue, but they were unable to explain it to us. It was only after I read the manual and figured out how to use the heater’s control pad to diagnose water flow that we learned of this flow issue. Using that diagnostic tool, we learned that my shower is drawing .6 GPM, the bare minimum to keep the unit heating. Evidently, it must drop below that minimum and cause the heating to stop. Marysia’s shower runs at .7, which is usually good enough to keep the heat on.
What are we going to do about this? Removing the heater would be a huge expense and is not really an option. Just today, I took the flow restricter out of my shower head, which may help. We’ll see tomorrow when I shower. Obviously, this is not a very earth-friendly solution.
It must say it burns my bacon that this expensive, high-tech, efficient heater does not function as well as the funky old wasteful system. I’m going to call Rinnai’s tech support tomorrow to see if they can offer any other solutions.
P.S. The minimum flow-rate issue is well described here (scroll down to “Minimum Flow Rates”):
http://www.profitableplumbing.com/_wsn/page5.html
Update 9/9/2007:
After trying for weeks to get the Hicks plumbers to come out and check our unit (and withholding payment), we finally wrote them a letter saying we would ask a different plumber to inspect our heater and deduct their service charge from our bill. This finally prompted Hicks to come to our house and check it.
His diagnosis was that it was a flow issue, although he said it was quite unusual for there to be a flow problem with showers. He made some adjustments to the shower heads and said we should try them for awhile and that if the problem persisted he would swap out our unit for another to see if it was defective. However, from looking at it, he could not see any problems.
One irony is that right after sending that letter, my shower started working properly. The heat stopped cutting off. Mysterious. This was at about the same time as the weather here finally turned cooler — after we in the South had suffered through the hottest August since weather record-taking began. For weeks, the “cold” water coming from the tap felt warm to the touch — evidently it was over 98 degrees. Could it have been that mixing this “cold” water with the Rinnai-heated water was a problem? Could the warm “cold” water coming into the Rinnai unit have affected its heating process? Could the water pressure in our house have been reduced in some fashion due to the record-setting high temperatures and accompanying drought?
The plumber was unable to answer these questions. So the reason the unit started operating properly remains a mystery, which is frustrating; because we have no guarantee that this problem won’t recur next summer.
The ambiguity of this situation leads me to believe that, at least in warm regions, the Rinnai water heater is not a wise investment.
I do plan to send an email to Rinnai explaining my experience. We’ll see if they respond.
Update 10/30/2007:
The Rinnai continues to work. I can’t help but suspect that the cooler weather has had something to do with it. Now that the temps aren’t over 100 on a regular basis, the heater seems to have an easier time knowing when to come on.
So, we aren’t dissatisfied enough to rip the system out, but I cannot say our experience with Rinnai water heaters has been a fully satisfactory one. Indeed, if I were given the opportunity to do it over again, I would not buy a Rinnai water heater.
Rinnai did respond to my email, but essentially they told me to talk to the plumber. They offered no further guidance.
Original Article Comments
When this article was posted on my original Crappy Software blog, it generated 17 outraged comments. After I discontinued that site (because Blogger turned to crap), I copied the comments over here to this much-improved, WordPress-based site.
Blogger MrPages said…
Could it be that in the hotter weather you take cooler showers? If you have less hot water flowing into the mix (your at the same overall flow rate, but less hot water flow rate) the hot water tank isn’t sensing enough flow. When it cooled down outside, you used more hot water and it works.
A possible solution might be (that you’ve stumbled on to without realizing it): Rather than turning the cold on and warming it up with hot, turn the hot on to a good flow rate and then add cold to cool it. This guarantees your hot water flow rate no matter how hot or cool you want your shower.
We’ve examined these too, and had decided not to go with one for other reasons (our water is too cold in the winter, the degree-rise of the units we looked at isn’t high enough to give us a good flow rate of hot water in the winter)
Thanks for this, there isn’t much non-company-sponsored info on people using these in North America.
10:04 PM
Blogger channel said…
One possible solution would be to add an extra controller in your bathroom and set the temp required on the keypad, this way you only need to turn on the hot water side and will receive the needed flow at the correct temperature-Phill@Channel Plumbing.
3:21 PM
Anonymous Gray Frierson Haertig said…
Try lowering the output temperature of the Rinnai.
This will reduce the amount of cold water that you need to add to temper the hot water to proper showering temperature and thus increase the flow through the Rennai.
As someone else suggested, you could add remote controllers in each bathroom and just set the Rennai output temperature to whatever your preferred showering temperature is. Then you just open the hot valve in the shower and ALL of your shower water flows through the Rinnai.
To a first order approximation, the energy cost is the same whether you heat the watter hotter than you need and temper it with cold water, or just heat all of the water to the proper temperature.
Gray
3:34 PM
Blogger Jeremy Butler said…
Yes, we tried lowering the temperature. Turned it so low that no cold water was necessary when showering. It still crapped out.
So, the idea of paying another plumber to come in and install a second controller (which we would also have to pay for) to set the temp each time we shower does not seem worth the expense. Plus, it would be a hassle one doesn’t have to mess with with a conventional water heater.
This week we had a plumber over for some other problems and I had him check the first plumber’s work on the Rinnai. He (the second plumber) said it looked fine.
In addition, although the hot water hasn’t cut out completely on me since the summer, the temperature does fluctuate slightly while I’m showering. Not a good sign.
Thus, what I wrote earlier still stands: if I could do this over again, I would not buy a Rinnai.
7:27 PM
Anonymous Anonymous said…
High inlet temperatures mean the burner may cycle when flows are low. Min firing for the Rinnai is 15MBH and if the flow is above the .6 gpm but still too low that the 15MBH is going to over heat the water the burner will cycle off for a few seconds. This results in what is known as “cold water sandwich” where a slug of unheated water gets into the hot water piping. Adding a small tank in the hot water line will absorb this, tank can be a 5 to 10 gallon electric and doesn’t have to be wired (if it is not the water inside will cool during periods of non use and will have to be flushed out each time the hot water is activated). It would be easier to change the shower heads to 1.5 gpm or greater and set the outlet temp to 110º or whatever your ideal temp for showering is. There are wireless remotes available as well to install in the bathrooms that are easier than pulling wires.
9:33 AM
Blogger Jeremy Butler said…
Interesting… So, even though the flow is above .6gpm it might still cycle off if 15MBH will overheat the water.
But what is MBH exactly?
Thanks for the useful comment.
8:00 PM
Anonymous Greg said…
MBH is 1,000 BTU or British Thermal Unit per hour, 1 BTU is the energy required to raise the temperature of one pound of water one degree farenheit. Min flow at 0.6 gallons is about 5 pounds of water per minute 300 pounds per hour, which will require 300 btus per degree of temperature rise. 15 MBH at 82% efficiency yields 12.3 MBH enough energy to raise the temp of the 300pounds of water 41 degrees which may exceed the setting on the heater causing the burner to cycle, setting the heater at a higher temperature won’t help as once you blend cold water with it your flow through the heater will drop below the .6 gpm.
My only solution would be to use less economical shower heads with flow rates sufficient to require the unit to fire at least minimum fire and flow.
2:33 PM
Blogger Jeremy Butler said…
Ah, I see…
So, if we assume the flow were near the minimum then it would run at 300 pounds per hour and the Rinnai is capable of raising that much water 41 degrees. If we further assume that the Rinnai is set to keep water at 110 degrees, then INCOMING water that is hotter than 69 degrees (110 minus 41) would cause it to cycle off because the Rinnai believes that heating it will put it over the 110 degree maximum. E.g., if the incoming water were 80 degrees, then heating it 41 degrees would make it 121 degrees — surpassing the thermostat’s maximum.
Thus, when we had a series of 100-plus degree days, the incoming groundwater was probably above 69 degrees and the Rinnai cycled off in order to avoid making the water too hot!
Very interesting… and frustrating. Wouldn’t this be a very common problem in warm-climate areas?
2:44 PM
Anonymous Anonymous said…
Saw your post on the Rinnai and felt I had to comment. I will start by agreeing with the anonymous poster that the minimum firing rate combined with the input temp can cause the unit to cycle in order to avoid overheating the water. I was told when I had my unit installed almost two years ago that these things really like to run at 1gpm or more minimum. We don’t have a problem with our shower, but our dish washer pulls about .65gpm so sometimes we see problems with that. Our combined problem is the fact that the dish washer only pulls about a gallon of water per wash, so the “cold water sandwich” mixes with what is supposed to be hot water and cools it even more. Add in the third strike of well water at a low of 35psi and we’re lucky the thing supplies hot water to the dish washer at all. We solved the problem by installing a 2 gallon point of use heater under the kitchen sink. Maybe you could do the same thing near your shower. I know it’s another strike on the energy efficiency scoreboard, but at least it’s not heating 30 gallons plus of standby water. The Rinnais are in my opinion one of the best tankless units on the market, but they do have their limitations.
2:39 PM
Anonymous Anonymous said…
Wish I had read this before I had a Rinnai installed. It’s been almost a month and I have had one good hot shower. The plumbers? have installed regulators on all appliances, removed the low flow indicators from shower heads, cleaned the filter so many times they finally broke it,(and which left water running from it. We were out of town so didn’t notice until 5 days later) and have almost driven me insane.
8:38 AM
Anonymous Anonymous said…
Looking into getting a tankless, the only two friends I know who have them experience this same issue. I just tested what .5 gpm would look like and it’s a strong stream to me. I rinse dishes in 1/4 of that flow.
Thank you for this article and all the comments. If you have any more news, let me know.
Otherwise I think I’ll stick with the big, ugly tank because I like hot water when I turn the faucet on and until I turn it off.
6:26 PM
Blogger Lamont said…
We have had a Rinnai for about 3 years… if you have hard water just dont buy one of these… you will constantly have chunks coming through, clogging filters etc. Youc an build yourself a pump and run vinegar through it once a month… but who wants to do that? This was DEFINATELY a bad decision!
10:43 PM
Anonymous Anonymous said…
I have had fluctuating temps with an upstairs shower where the pressure is lower than the downstairs. After much head-scratching, I found that if I leave the SINK hot water running about 1/3 – 1/2 way while I take my shower, no problem. Wasteful, but cheaper than re-doing plumbing.
9:31 PM
Anonymous Anonymous said…
Hey, thanks for the great post! I just had a Baxi tankless hot water / heating combo unit installed two months ago, and I have been having similar problems. No one tells you about the possible low-flow issue when you’re looking at these things, but it must be really common! In my case, at a gallon per minute, the water temperature fluctuates about 10 degrees F. Like you, plumbers kept coming over and saying “Hey, it’s fixed” but the problem persisted. Finally they took out all of our airators and flow-restrictors, which seems to me a terrible solution! I mean, I installed the thing to be MORE energy efficient! Now I have to use MORE hot water than I want to! I feel like the shower is beating me to death, it’s so strong!
Today we finally had a Baxi representative here, and after taking the whole thing apart and putting it back together, he basically said, that’s the way it is…
It has been summer here, so I’m thinking that the input temp may be the issue for us, as some here have described. I’m going to try to lower the water temp so there is a greater flow of hot water and less cold, but it looks like I’m just going to have to live with crappy showers during the summer months…
8:02 PM
Anonymous Anonymous said…
I too turn on the bathtub hot water when showering. Works fine now. BTW, at first used the sink, not the tub, until I neglected to notice that the drain was closed. DUH!
10:48 PM
Blogger Ralf Thompson said…
Well tankless water heaters are efficient and great these can’t heat the water like other water heaters but these are good too.
8:19 AM
Anonymous Anonymous said…
i also have a tankless water heater. all the same issues. i turn on the sink faucet while i shower. in the winter the heater shuts off because there’s also a MAX FLOW setting? WTF? it seems as though a quick change to the crappy software would do the trick. why does the min flow have to be 0.5 gpm? i understand it has to sense the flow, but that is clearly too high for many of us in the real friggin world. my kitchen faucet has a 0.2 gpm max flow. these settings make no sense.
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