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Does a tankless water heater require a pressure relief valve?
Saturday, June 30, 2018
Whether or not a tankless water heater is required to have a pressure relief valve depends on what the manufacturer states in the installation manual. The manual for Titan electric water heaters, for example, does not require a pressure relief valve, except if your water supply piping is plastic. Here’s an excerpt from their manual:
The Takagi gas-fired tankless water heater manual specifies a pressure relief valve on the hot water outlet. Here’s an excerpt from that manual:
So consult the manufacturer’s installation manual. Gas-fired tankless water heaters will usually require a pressure relief valve, while electric on-demand water heaters may not. The manufacturers typically only require a pressure relief valve, not the combination temperature and pressure relief valve that is necessary for tank-type water heaters.
There is also one further complication to this issue. While both the International Residential Code (IRC) and the Florida Building Code (FBC) state in one section of the Codes (M2005.1) that water heaters should be installed per manufacturer’s instructions, another section of the Codes reads as follows:
The installation manual for Rheem electric tankless water heaters tactfully resolves the issue with this statement: “Tankless water heaters are not required to be equipped with a Pressure and Temperature Relief Valve (PTRV). If the local inspector will not pass the installation without a PTRV, it should be installed on the hot water outlet side of the unit.”
That’s good advice. A structural engineer we used to work with in the Florida Keys, Paul Mitchell, suggested to us after a struggle with a county inspector at our jobsite that “Never argue with an inspector. It’s like wrestling a greased pig. You will lose...and discover that the pig likes it.”
The Titan tankless water heater in the picture at the top of the page was in a homeowner-remodeled house we inspected today, and is the inspiration for this article. The defects in the installation included:
- No required pressure relief valve at hot water side, because piping is CPVC.
- No required copper piping for first three feet from unit at both sides, as specified by manufacturer when plastic pipe is used.
- No required cold water shut-off valve.
- Unprotected NM-cable connected to water heater.
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