Seisco TWH does not need a TPR valve?

I walked into the garage this morning at my first inspection and saw a Seisco tankless water heater without a TPR valve on it. The installation instructions were behind it so of course I grabbed them and proceeded to read. I was shocked when I read that in Manufactured Homes a TPR valve is not required per HUD(this is not a Manufactured Home)??? Moreover the manufacturer is claiming that per NEC 422-47 the TWH does not need a TPR valve unless "local codes require it.
What gives here? Seisco is selling this as not needing a TPR valve, so the cost for installation is less, but the IRC says it needs a TPR valve. I called the mfr from the inspection this morning and they immediately said “why yes it needs a TPR valve if your local jurisdiction calls for it” I said I was quoting the IRC.
I know I don’t need need to ask for opinions here, but hit me with your best shot. Model RA-28 electric TWH Thanks in advance.
PS, I recommended a TPR valve be installed.

Since there is no holding tank, it may not be as serious of an issue.

From the Seisco website:

Also see: Tankless W/H post and NACHI TV on Tankless W/H

Jerry, it would appear that the only reason a TPR would be required is if it is mandated by local codes.

At least that is the way I see it.


A temperature and pressure relief valve (T&P Valve) may be required by local code.

When a T&P valve is installed (which is not provided by the manufacturer), it should be checked after the water supply to the heater is turned on. With the water supply on, there should be no water flowing from the valve. Operate the valve manually two or three times to purge the trapped air from the top of the heater’s chamber. CLOSE VALVE. Water should stop flowing completely prior to connecting the drain piping to the valve.

SINCE THE SEISCO HEATER DOES NOT UTILIZE A STORAGE TANK, THE USE OF A T&P RELIEF VALVE IS NOT REQUIRED BY MANY NATIONAL STANDARDS, INCLUDING UL STANDARD 499. Seisco heaters are designed with control logic as well as elctro-mechanical high limit thermostat switches for over-temperature protection. With these built-in safety features, the use of a T&P Relief Valve is not required.


Marcel :):smiley:

So it is more that there is no stored water than it is that it is a “water heater”. Thanks guys.