How to route a TPR in an interior room

[spryde]

I am finalizing the plans for the house we are building and we will have a second floor laundry with a tankless water heater installed in that room (direct vented to the roof). The unit will probably be a Rinnai and the install instructions says that the appliance really doesn't need a TPR valve.

Question 1: Do you guys put a TPR on this unit?
Question 2: If you were to put a TPR on this, how would you route the outlet of the TPR? I will have 16" floor trusses below the room and the nearest exterior wall will be 5' through said floor trusses. This is a two story house with a garage on the first level. The outlet could be centered between two garage doors (spaced 2' apart). I will be under the Michigan Residential Code with is 2003 IRC based (For non-residential units, we are under the 2006 IPC).

Thanks!

SP

 

[Jimbo]

I don't know your code. Here in California, it MUST go outside, and the line must run continously downward, no bellies. There is an exception, and in some cases they will allow you to put a Watts 210 hi temp gas shutoff on the tank, and a pressure relief valve on the outside of the dwelling. This would probalby not be allowed at all on a tankless.

I would take another look at your installation instructions, as it doesn't seem right that they would use iffy language to the effect that you "might not really need it". The local code and inspector would have the final call on that, in any event, so check with them.

 

[Sponsor]

 

[hj]

valve

They NEED a pressure relief valve, but I prefer to install a T&P valve just in case all the bells and whistles fail.

 

[spryde]

I wonder if I put a floor drain in that room (trapped of course) and run the TPR pipe to the drain, would that suffice? It would be in conditioned space, not directly connected to the drain system and there will be an air gap. I am not under 2006 IRC yet but I do personally agree with the reasoning behind most of the 2006 changes to address TPR issues.

SP

 

[hj]

tpr

A floor drain is not an "approved" terminus for a relief valve line because it usually has a grid over it which would cause splashing and possible flooding in the event of a discharge from the safety valve.

 

[spryde]

Good to know. I guess will have to think about this one quite a bit more. We are subjected to freezing conditions here so doing a direct dump outside at the foundation line is pretty much out of the question unless I am misinterpreting the meaning or spirit of the new rule.

I missed this earlier about the iffyness of the statement. Here is the exact wording:

An approved pressure relief valve is required by the
American National Standard (ANSI Z21.10.3) /
Canadian Standard (CSA 4.3) for all water heating
systems.

Last part of that section states:

Neither Rinnai nor the American National Standard
(ANSI Z21.10.3) / Canadian Standard (CSA 4.3)
requires a combination temperature and pressure
relief valve for this appliance. However local codes
may require a combination temperature and
pressure relief valve.

Since we are still under 2003 IRC, there really is no code for the TPR valve plumbing. It is either up to me or the local AHJ if they really care enough to say yay or nay. Personally, I would run down through the floor, over to the outside via the truss space and down the outside wall cavity (between the insulation) to 24" above the ground. I don't see a problem with freezing because the if there becomes a pressure situation, it is usually associated with the heat generating it and the heat will blast any ice out of the way as it heads toward the earth. I would sincerely doubt my well would be able to generate that much pressure.

As always suggestions, flames, and "are you insane?!?!?" comments are welcome!

SP

Final Edit: And thanks. I do appreciate the information and knowledge!