TPV drain line

[Bwanap]

Got two 40 gal heaters, one leaked, not surprising as 30 years old. Installing a single Rheem 9gpm tankless. Planned to use the existing TPV connection. Opened up the false bottom in garage (had to, all wet, no drain pans). I see that the 3/4" copper lines from the two old tanks combine and disappear into slab. These drain lines need to be gapped I believe, so is this line likely just headed outside somewhere I've not noticed before?

If so, can I use one branch for the TPV and the other for the drain pan? Just wondering if released under pressure it could come back up into pan? Those Camco pans are pretty big though, and obviously shouldn't be a lot of water releasing from a tankless.

Just for a laugh, original builders connected the 3" double wall vents together, used 9 elbows to do so! It's like a transformer or something.

 

[Breplum]

Combining Temp/Pressure relief valves together is not a good practice. Not to code in most jurisdictions because the point of having them required to be day-lighted is to be able to tell which one has failed in case of dripping.
Daylighting drain from safety pan is preferred, but if you ran a 1" drain from a safety pan on your new tankless, then you could tap together if downstream enough to not to backflow into the safety pan.

 

[Sponsor]

 

[Fitter30]

A catch pan for a tp relief devise is like there is no way it's big enough. A devise could fail wide open or at least fail part open.

 

[Bwanap]

Combining Temp/Pressure relief valves together is not a good practice. Not to code in most jurisdictions because the point of having them required to be day-lighted is to be able to tell which one has failed in case of dripping.
Daylighting drain from safety pan is preferred, but if you ran a 1" drain from a safety pan on your new tankless, then you could tap together if downstream enough to not to backflow into the safety pan.

Trying to figure out existing system, if it's not to code, that wouldn't surprise me. There's one line to left for TPV connected to existing tank, there's one from removed tank (light hanging on it), below, they tee together and into slab. I see nothing outside that could be this line daylighting.

I could run a one inch drain pipe from pan, to the right through outside wall of garage. So, can I just have TPV open to pan then? Or should/can I use that existing line (capping off one leg)?

 

[Bwanap]

A catch pan for a tp relief devise is like there is no way it's big enough. A devise could fail wide open or at least fail part open.

The TPV is 3/4", if the drain line is 1", I would think that would work?

 

[Fitter30]

The TPV is 3/4", if the drain line is 1", I would think that would work?

Run a separate lines outside that pan under the heater if the tpv would let go water would be splashing out of it

 

[Jeff H Young]

608.5 relief valve shal discharge independantly, relief valve must not discharge into drainage pan. Im Asuming this is in Austin tx and under upc plumbing code. look that code number up for more details