You can connect a propane tank of nearly any size to your household hot water heater as long as you satisfy three conditions: You need to install a pressure regulator between the tank and hot water heater, ensure that the hot water heater is equipped for propane rather than natural gas, and maintain the correct safe distance between the tank and the hot water heater.
The sizes of some fittings might vary with the needs of your water heater control box. Some gas appliances come with kits that include some of the fittings you'll need. Improve safety and simplify the task by having the hardware store cut and thread your pipes. Set the propane tank on a low, flat platform made of bricks or cinder blocks, so that it is stable and level.
The propane tank needs to be at least 10 feet from the water heater.
Some municipalities might require a greater distance, so check local regulations in case you need more than 10 feet. The propane tank should not be under an awning or other shelter that could retain vented gas from the propane tank.
Dig a inch-deep trench between the water heater and the propane tank. Some municipalities might require a greater depth, so check local regulations. Smear plumber's paste on the threading at both ends of the foot pipe and screw elbows onto each.
Make sure that both the installed elbows face in the same direction when completely screwed on. Hand tighten and use a pipe wrench on each side of the union to tighten it one more turn.
Hand tighten and use a pipe wrench on each side of the union to tighten them one more turn. Repeat at the other end of the foot pipe. Place the assembly in the trench with the two pipes at either end pointed up. Place a piece of tape over the open pipes to ensure that no dirt or debris falls into the pipes as you complete the installation.
Take the tape off before you screw on additional pieces. Place plumber's paste on the threaded pipe nearest to the water heater and screw the shutoff valve onto that.
Hand tighten and use a pipe wrench on each side of the union to tighten the union one more turn. Smear plumber's paste onto the threaded side of a male pipe-to-flare adapter and screw that into the top of the gas valve.