Would you believe a simple device costing less than $25.00 installed improperly could level your house? This device resides on your hot water heater / tank . It’s a temperature pressure relief valve (TPRV) which should be located within the top 6 inches of your hot water tank immersed in water.
To keep it simple I will only discuss hot water tanks. The main purpose of a hot water heater is to heat the domestic water and supply it to kitchens and bathrooms etc. Water heaters are potential explosion hazards if not properly installed. There are instances where hot water tanks with improperly installed safety devices have been propelled through floor and roof structures and over 100 feet into the air. Exploding 30 gallon water heater has the force of about 1 pound dynamite enough power to destroy a home and kill or injure those inside.
Because of the potential hazards, there are standards that regulate the materials, design, and installation of water heaters and their related safety devices. Certification marks from approved agencies on water heaters are required to indicate compliance with approved standards.
Most tanks are insulated steel cylinders with an enamel coating on the inner surface. They are referred to as glass-lined tanks. The lining helps prevent corrosion. Conventional residential water heaters have life expectancies that vary greatly.
Combination temperature and pressure relief (T & P Relief or TPR) valves do two things:
1) they open and release water out of the tank if the temperature exceeds 210°F (just below the boiling point), and 2) they will open if the pressure in the tank exceeds 150 psi, they start dripping(the maximum normal operating pressure for a water heater.)
The picture above is from a recent home inspection. First problem , notice the expansion tank to the right of the hot water heater. The expansion tank is installed improperly. It should be installed on the input cold water side of the tank. In this case its installed on the PRV outlet doing nothing.
Second, problem if you understand the design of the pressure relief valve you’ll notice it to is installed improperly. It is not inside the tank therefore if the water within the tank exceeds 210° the wax rod will not melt due to its location.
When installed on the end of a “T” fitting the T fitting and the piping acts as a heat sink dissipating the heat across the T fitting and the piping. This prevents the wax rod from melting and releasing the overheated water as designed. If an extended rod is used not an issue. Only way to confirm this is looking at the tag. If a 4″ rod is installed it needs replacement.
Recommend contacting a plumber and have this checked if your hot water tanks PRV looks like this.
Same issue applies here on a pressure relief valve installed improperly on a boiler. Another safety hazard is the PRV is missing the extension which should extend 6″ above the floor.
Same story, different house, taken 10.4.12, see below.
Note the tag clearly states 4″ rod. Which means the rod “is not inside the tank“. Problem waiting to happen. More interesting is a building contractor owns this home.
Relief valves must be third-party tested. The certification mark is the indicator that the valve has been tested. Temperature relief valves must be set at a maximum temperature of 210°F (99°C). The valve is designed to dissipate energy at a rate (BTU rating) equal to or greater than the energy/heat input rate (BTU rating) of the water heater. A relief valve opens in proportion to the temperature and pressure forced upon its closure disk. The higher the temperature or pressure, the greater the force, and the more the valve opens.
The valve must be set to 25 psi (172 kPa) above the system, but not over 150 psi (1035 kPa).This setting should not exceed the tank’s rated working pressure. An undersized valve would not be able to prevent pressure from exceeding the maximum capacity, and a dangerous situation could result. The result could be an explosive tank rupture accompanied by an instantaneous release of enormous thermal energy stored in superheated water inside the tank. It could propel a water heater like a rocket through multiple stories and the roof of a dwelling.
A temperature and pressure relief (T&P Relief or TPR) valve should be installed on all storage water heaters operating above atmospheric pressure. Tankless water heaters must have TPR valves installed. Water heaters without this protection can produce explosions and have been responsible for many deaths.
Boilers should be equipped with pressure-relief valves with minimum rated capacities for the equipment served. A boiler operates at a maximum water pressure of 160 psig and at a maximum water temperature of 250°F (121°C). Pressure-relief valves should be set at the maximum rating of the boiler. Discharge should be piped to drains by gravity to within 18 inches (457 mm) of the floor or to an open receptor. If no drain is provided 6 inches from the floor is recommended.
What I find most interesting is plumbers and heating technicians had to of serviced both these units over time and never noticed the pressure relief valves improperly installed.
More information can be found on ASME Section IV on boilers.
Enjoy this Mythbusters video!
