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Rick, Construction Supervisor
Category: Plumbing
Satisfied Customers: 21377
Experience:  Licensed Master plumber with 40+ yrs. experience.
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I want to replace two hot water heaters with one in my ranch

Customer Question

Hi Mark, I want to replace two hot water heaters with one in my ranch style home with crawlspace. I have a 40gal tank in a newer addition laundry room for the main/single tank, and I will remove a natural gas lowboy heater in a crawlspace in the older part of the house. Here's my (rough) plan:
- purchase a Grundfos Pump; looking at a model with built in check valve and temperature sensor (I do not need or want a timer) My supply lines at the tank are 3/4" but I don't see where Grundfos makes a 3/4" FNPT pump, only 1/2 and 1 1/2", so I will need to install adapters.
- pump will be mounted on top of the heater at the hot water outlet, temp sensor attached to hot water line.
- I will install a 1/2" pex return line in the crawlspace and connect it to the farthest hot water supply line/fixture (connected to the hot water line, not the cold water line, correct?)
- Connect the 1/2" return line directly to the drain valve on the water heater. With this connection I do not need a check valve or expansion tank on this line, correct ??
With this system and model of pump I should see the pump kick on an off depending on the temperature sensor reading, and be able to receive hot water at all fixtures in a reasonable amount of time. I note that I am on a well and not all that concerned about losing water down the drain. Thanks,
Dave, Colorado Springs, CO
Submitted: 1 year ago.
Category: Plumbing
Expert:  Rick replied 1 year ago.

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. If my initial response doesn’t answer your question then let me know and we can

continue our conversation.

You want to install the pump on the return at the bottom of the tank not at the top of the tank. All you need is a 1/2" return line. That's why Grundfos only makes a 1/2" pump. You also want to remove the tank drain, install a 3/4" brass nipple then screw on a 3/4" X 1/2" brass TEE. Your drain goes into the end of the TEE your return into the 1/2" branch. If your pump has a built in check you don't need another one. An expansion tank is only necessary if you have problems with the temp & pressure relief valve discharging. You can install the expansion tank (if you need one) on the cold water line near the tank.

Customer: replied 1 year ago.
install the pump on the return at the bottom of the tank". Isn't it better to pull water from the top than pushing it all the way through the tank?
Expert:  Rick replied 1 year ago.

The return pump always goes on the return line at the bottom of the tank in a case like yours. You're only moving enough water to keep the water in the line hot. Why do you suppose Grundfos only makes a 1/2" return pump when every water heater has 3/4" inlet and outlet connections. Your plan can work except that you're significantly reducing the hot water flow to the fixtures by reducing to 1/2" to accommodate your pump. Stick with the config that's standard practice.