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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Here’s links to a collection of more blog posts about WATER HEATERS:
• Are water heaters required to be raised off the floor?
• Can a Temperature and Pressure Relief (TPR or T&P) valve be mounted to discharge horizontally?
• Where are gas water heaters not allowed to be installed?
• Is the minimum size water heater inlet pipe 1/2" or 3/4" according to the building code?
• Can you use a light switch for a water heater disconnect?
• How can I tell if a water heater is HUD-approved for mobile/manufactured homes?
• Can you wire a 240-volt water heater with 120 volts?
• Is it alright to have a shut-off valve on both the hot and cold water pipes at a water heater?
• What is the minimum clearance to doors and windows for an outdoor tankless gas water heater?
• What is required clearance for access and working space in front of an electric water heater?
• Why is the water heater older than the house?
• Does a water heater need a shut-off valve?
• Why should a tankless water heater have an isolator/service valve kit installed?
• When was a gas water heater first required to be elevated 18 inches above a garage floor?
• Can the temperature and pressure relief (TPR) valve discharge pipe for a mobile/manufactured home water heater terminate under the home?
• What is the purpose of a thermostatic mixing valve above a water heater?
• Does a tankless gas water heater still work with no electricity during a power outage?
• Why do water heaters have a sacrificial anode?
• What is the difference between a manufactured/mobile home water heater and a regular water heater?
• When is a water heater drain pan required?
• Why is there water in my water heater drain pan?
• What does it mean when a water heater Temperature/Pressure Relief (TPR) discharge pipe is "trapped"?
• Can I leave a gas water heater in place when remodeling a garage into a family room or bedroom?
• Where do I find the water heater in a mobile home?
• Does a tankless water heater in an attic require a drain pan?
• Does an electric water heater require a disconnect?
• Is a catch pan and drain piping required for a replacement water heater?
• What is the difference between a single element and dual element electric water heater?
• What is an FVIR water heater?
• What is a heat pump water heater?
• What is a dielectric union?
• What's that powdery crust on the pipe connections at the water heater?
• What are the most common installation mistakes with water heater replacement?
• Why is my water heater making strange (rumbling, gurgling, knocking or banging) noises?
• What can I do to make my water heater last longer?
• How can I determine the age of a water heater if the serial number is missing or decoding it is impossible?
• How does a hydronic heating system work?
• What is the difference between a regular water heater and a direct vent water heater?
• What is the difference between a regular water heater and a power vent water heater?
• What is backdrafting at a gas water heater?
• How do I determine if a water heater is gas or electric?
• What does it mean when a gas appliance (water heater, furnace, or range) has been "red tagged"?
• What's the valve with the flip-up handle on the water heater for?
• Why is an older water heater an insurance problem?
Visit our WATER HEATERS page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.