Relief Valves on Tankless Units

[Brian G]

I just ran into my first tankless/on-demand/continuous/you-name-it water heater, in the outside wall of a house. Does anyone know what's suppose to be done with the relief piping on these models? It looks to me like any discharge will probably leak into the wall around the penetrations, but there was no sign of a planned opening in the cover for a relief pipe.

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I found clearance specs, so I already know it's too close to the window, but nothing about the relief piping. Anybody?

Brian G.

"Relief" For My Ignorance Please [:-dunce]

[Brian G]

I found it. They say "Pipe pressure relief discharge to a drain or outside environment". This guy didn't pipe it to anywhere.

Brian G.

Dat's a No-Gooder [:-paperba

[Richard Moore]

Hi Brian,

This from Rinnai.

My bold.

INSTALLER’S INSTALLATION INSTRUCTIONS

Pressure Relief Valve

1) ANSI code calls for the addition of an approved pressure relief valve to all water heating systems.

2) The pressure relief valve must meet the following criteria: The relief valve must comply with the

standard for Relief Valves and Automatic Gas Shutoff Devices for Hot Water Supply Systems ANSI

Z21. 22 and/or the standard CAN1-4.4 Temperature, Pressure, Temperature and Pressure Relief

Valves and Vacuum Relief Valves. This relief valve must be rated up to 150 PSI of pressure.

3) The relief valve should be added to the hot water outlet line per manufacturer's instructions.

DO NOT place any other type valve or shut off device between the relief valve and the hot

water heater.

4) The discharge from the pressure relief valve should be piped to the ground or into a drain system to

prevent exposure or possible burn hazards to humans or other plant or animal life. Water discharged

from the relief valve could cause severe burns instantly, scalds and/or death.

5) Do not plug the relief valve and do not install any reducing fittings or other restrictions in the relief

line. The relief line should allow for complete drainage of the valve and the line.

6) If a relief valve discharges periodically, this may be due to thermal expansion in a closed

water supply system. Contact the water supplier or local plumbing inspector on how to

correct this situation. Do not plug the relief valve.

7) Pressure relief valve must be manually operated once a year to check for correct operation.

Caution: See Item 4 before manually operating relief valve.

Should overheating occur or the gas supply fail to shut off, turn off the manual gas valve on

the Rinnai.

[Richard Moore]

Took me a while to find this. I believe I've only seen 3 or 4 of them. Anyway, here's one with the valve plumbed.

(crappy wiring connection)

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[mthomas1]

Actually, though the drain line is wrong I've seen much worse installs, for example it's nice to see those Webstone valves as it makes backflushing the unit much easier. If you are new to tankless units some things to watch for when inspecting their the relief valves are that 1) tankless manufactures generally specify PRVs rather than TPRVs (though local codes may still require the latter) and 2) the larger capacity units (such as the Takagi T-M1) require higher capacity PRVs than most of us are used to seeing on residential water heaters.

If you don't see a lot of tankless units these you may find this useful, it's a page I've put together based on my experience installing and inspecting tankless units:

http://www.paragoninspects.com/tankless ... l-faq.html

[Brian G]

Thanks Richard, that looks like the same pdf I found. I took from an earlier, shorter part because I don't know how to copy text from a pdf (pg. 26, part 6). How you do dat? [?]

Mike, that's a ton of info, thanks. Duely bookmarked for future use...don't go out of business on me. []

Brian G.

Home Inspection.....It's a Tankless Job [:-paperba[]

[Richard Moore]

Originally posted by Brian G

Thanks Richard, that looks like the same pdf I found. I took from an earlier, shorter part because I don't know how to copy text from a pdf (pg. 26, part 6). How you do dat? [?]

[:-paperba[]

I just highlighted the text, copied and pasted in the normal way as I would from, say, a DOC file. I know that some PDFs are protected (somehow) to prevent this, but my experience is that most that I want to grab text from aren't. So, I just try to see if it will allow me to do so. I have a screengrabber utility (to JPG) when that doesn't work.

[Phillip]

Brain G.

Here is what I see in this area.

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[Nolan Kienitz]

TPR on tankless should be treated same as 'tank-types'.

This according to several plumbing folks in the DFW market I've talked with and from what I read in the IRC ... as clear as mud as that can be sometimes.

Routed to exterior within ~ 6-inches of grade. Now the 2006 IRC has a whole new twist on TPR drains for W/Hs and it is presenting a new can of worms/possibilities ... so to speak.

[Lee Place]

Good Morning,

The PRV shown in the first post should be piped into the side port of the hot water flush valve or between the hot water flush valve and the tank, not after it, (Ranni Instalation Instructions item 3).