The Rheem ProTerra hybrid heat pump water heater

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My gas-fired tank water heater (or boiler) developed a leak in 2021 and had to be replaced. After trying out an oversized gas tankless water heater for a couple of months, I decided to install a 50 gallon Rheem ProTerra hybrid heat pump water heater. It’s amazing how the heat pump, a small fan blowing over recirculating refrigerant, can heat water to 120ºF while cooling down the surrounding area. The hybrid part of this water heater means that it can fall back to using electrical heating elements to keep up with demand.

Its main advantages are:

But, I also understand now why these water heaters aren’t more common:

Anode rod

A common complaint about this water heater is a sulfur smell from its water as its stock magnesium anode rod corrodes. Anode rods are crucial to extending the life of a tank water heater, but they need to be replaced about every two years because they’re sacrificial and designed to deteriorate before the lining of the tank. One fix is to chlorinate the incoming water, but this still leaves me with the biannual rod replacement.

To avoid the potential for smelly water and hassle of replacing an anode rod down the road, I bought a Corro-Protec powered anode rod. The rod itself is a lot smaller than a conventional anode rod and needs electrical connections to the rod and the tank, to act as a ground. This was by far the most complicated part of the install and it’s unclear if it was worth it.

The anode rod is located inside the heat pump chamber on the water heater, so the top cover plate needs to be removed to access it. The stock anode rod has a 1 1/16“ bolt that’s surrounded by a plastic cover, probably to protect the insulation around the tank. This plastic cover needs to be removed to make it possible to fit a socket around the bolt and let it turn freely. Some people use a Dremel tool to cut away the plastic, but this can be messy. The best way to do this is to use a small plastic spudger to lift up the edges of the plastic and then grab it with linesman pliers. I was able to twist the plastic out of the hole after 15 minutes of yanking and spinning.

The cavity into the unit is about a foot deep so the socket needs an extension bar to reach the bolt. Even with a 15“ ratcheting breaker bar, I couldn’t budge the bolt. I rented a 18V cordless impact driver later on and was able to dislodge it fairly easily. I put some teflon tape on the new anode rod and tightened it down with the ratchet.

The cavity where the anode rod is located is air-tight for efficiency, so I had to drill a ½“ hole in the top cover plate to run the wire. The sides of the hole will be sharp, so it’s a good idea to put a plastic bushing or masking tape to prevent fraying the cord. For a ground connection, I used the green screw that’s used to ground the unit with the incoming circuit.

PEX plumbing

Copper, CPVC, and cross-linked polyethylene (PEX) piping are the current state-of-the-art for making plumbing connections for potable water. Properly soldering copper pipe connections can take months of practice, leave a mess, and fixes the water heater in place. CPVC is another option that’s easier to install, but is also messy and relatively rigid. Because drywall has to be installed behind this unit after it’s been inspected, I opted to use flexible PEX pipes. The PEX-B composition is said to leach less chemicals into the water, but no PEX pipe should be used where it could be exposed to the sun or UV light sources. PEX is also much less expensive than copper piping.

There are three typical ways to make connections between PEX lines:

The connections to the water heater use Sharkbite because of how easy it was install and all of the connections are outside of the wall, so they can be monitored. The fittings alone were about $10 each, and we needed about half-a-dozen elbows to accommodate the hot and cold water connections.

Drain pan

It’s unclear if a drain pan is necessary with the unit installed on a concrete slab, but a lightweight plastic pan helps scoot the unit around during installation.