Instantaneous water heaters, best practices, watch out fors, etc

[phishfood]

I have noticed over the past year and a half several threads about weird issues with instantaneous water heaters, usually having to do with temperature fluctuations. And I remember a manager for a small residential company a few years ago trying to steer customers away from these units because of problems they had experienced with them.

All of this makes me think that we as an industry need to do a better job educating ourselves, making a better product, doing a better install, educating our customers, demanding better support from manufacturers, etc.

So hopefully this thread will be a step in that direction. Please post your experiences with demand water heaters. What problems did you run into, what did you do to resolve them? What have you fixed on someone else's install that the rest of us need to watch out for? What models/manufacturer's have you had the most problems with?

Maybe if I get ambitious I will look through this forum and post links to some of the threads. Don't hesitate to do the same.

[havasu]

I too have read some really interesting problems with temperature fluctuations with TWH's. I myself have had my Navien for nearly 19 months, and have yet to experience any of the problems listed. I have the temp. control set at 120*, and set it to recirculate twice a day (8 AM and 11PM). My best recommendation is to always install a recirculating system with them.

[Hyper48fan]

I had a call where the homeowner had only been there a week and when they used the Roman Tub in the master bath the hot water would work for a second or two then it would go cold. I looked for a mixing valve but could not find one. When using the tub no other fixtures in the house got hot water, but you could use multiple combinations of any other fixtures and get hot water. I closed the shut offs on the shower valve in the master next to the tub and pulled the cartridge, no debris plus the shower worked fine. I went into the crawl and looked for cross connections but could not find one. I throttled down the hot side of the Roman Tub valve to equal that of a lav or sink and it worked, the hot stayed hot. The tankless water heater didn't have a manual and it didn't have a manufacturer name on it. It had a serial number, BTU's (90,000) and I can't remember what else but there was not enough info to call a manufacturer. The only thing I could think of was that the Roman tub was exceeding the demand.

[Caduceus]

Great thread starter, phish. For a few years it has been an issue that these appliances are being installed in less-than-adequate conditions for performance. The excitement of having a new item, getting a federal tax rebate or the greed of making a sale distracts from the potential faults of installing them. Some of the manufacturers make qualifying information available, but nobody really wants to hear that they are not a good candidate for a tankless heater when their heart is already set on it.
By sharing information we may be able to open some eyes on the matter. I do believe that tankless heaters are a fantastically efficient way to heat water. Hot water can now be provided where it was once considered a major project and the freedom to design has been opened up because of it's size and ease to install.
On the other side of the spectrum, a consumer reports evaluation showed that the actual savings annually are not significant and when replacing an existing tank there are really no savings at all over the lifetime of the tankless.
I live in the north where the ambient water temperature can be 55 degrees F. in the winter. A friend asked if I could install a tankless for her whole house. I checked her temperature (58 deg. F.) and assessed the potential demand. To maintain temperature with demand and to avoid "cold spells" in water supply, she would need $2,500-$3,000 unit providing 14 GPM at 199,000+ BTUs. I could not, with clear conscience, install anything less.
She consulted another local plumber who said "no problem" and is recommending a 5 GPM tankless @ 122,000 BTUs. A huge difference in opinion. We'll see what she does this summer during the remodel.
I would never say it, but an "I told you so..." may be lingering in the air.

[LiQuId]

I have gone to service one that was COMPLETELLY blocked off with mineral deposits, vinegar did the job.

After talking with the owner I discovered that the unit had been in operation for only 2 months and that they were previouslly advised to not install an instantanious heater as the water in the area is known to be mineral rich.

basically they got screwed by a company that didnt care about conditions, only sales. and clearly sice i was called in they had no warranty or did not honor it.

[LiQuId]

It was a rinai If memory serves

[phishfood]

Good responses so far, keep them coming.

[havasu]

Although I have a 4 bed/2 bath home, I just went outside to check the stats on the Navian TWH. It is rated at 199,000 BTU's, and the recovery rate is 301 GPH. It seems like most I have read about are quite a bit smaller, which is possibly why they don't seem to work well?

[Caduceus]

Yeah, your location and the size of the TWH sound like a good match already. What helps to determine the temperature rise that the unit can handle, in realtion to the GPM, are the BTUs. Most manufacturers provide a chart that will show the GPM with temperature rise and also the type and size of appliance that will match what you need. It would be in their best interests to educate the public about their product. I would hate to be a customer service rep that has to deal with upset customers and then tell them they had the wrong appliance installed.

[Hyper48fan]

Our suppliers give classes that last a few hours, to educate plumbers about all of this stuff, I've yet to attend, but I've read up a lot.