Watts 100XL-150 3/4 3/4 In Brass Self Closing Temperature And Pressure Relief Valve, 150 psi, 210 degree F, Test Lever, Extension Thermostat

The 100XL-150 is the short shank version at 1-1/8 inches, with a 3 inch copper thermostat probe extending past it into the tank. That combination is meant for tanks where the tapping sits close to the water. If your heater has deep foam insulation or a recessed tapping that needs more reach, you want an extended shank T&P instead, because a short shank forces the probe to sit shallow and the valve can trip late.

No. The 100XL-150 is a brass valve that is not lead free, so it should not be used where lead free construction is required for potable water. Most jurisdictions require lead free wetted parts on domestic hot water systems. For a potable water heater, specify the lead free equivalent in the same series.

The 100XL-150 is factory set to relieve at 150 psi and at 210 degrees F. That 150 psi setting is the high end of the 75 to 150 psi range the 100XL series covers, so it is intended for tanks with a working pressure rating that matches. If your heater's data plate lists a lower maximum working pressure, you need the lower set point version, not this one.

Its temperature steam discharge capacity is 105,000 BTU per hour. The valve's rated capacity has to equal or exceed the input rating of the water heater it protects, so this one covers heaters up to 105,000 BTU/hr input. A larger commercial heater needs a higher capacity valve.

Both. The 100XL-150 is a combination temperature and pressure relief valve: the 3 inch copper probe senses tank water temperature and dumps at 210 degrees F, and the seat relieves at 150 psi independently. A plain pressure-only relief valve will not protect a water heater, which is why code calls for a T&P on storage water heaters.

It is self closing. Once the tank pressure or temperature drops back below the set point, the valve reseats on its own rather than staying open. It also carries a test lever so a maintenance tech can manually lift and flush the seat during annual checks, which is the standard way to verify the valve has not seized.

Yes, a full size discharge line is required and none is included with the valve. The outlet is 3/4 inch female NPT, so the drain line runs in 3/4 inch pipe, never reduced, pitched down to terminate where discharge is visible and cannot scald anyone. Plan that pipe as part of the job, along with thread sealant for the 3/4 inch male NPT inlet.

The 100XL-150 is flagged USA for Buy American Act compliance, which matters on federally funded institutional and government work. The Watts part number to put on the submittal is 66100, model 100XL-150 3/4.