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Ultimate Electric Hot Water Heater Setup

I installed my first Rheem HP50 Hybrid Heat Pump water heater in 2009, and that first unit has been fantastic for my clients.  I’ve tried several models over the last 6 years (including one that’s no longer made), but the biggest downfall of these Heat Pump units is their capacity.  You really want to run your unit in Heat Pump Only mode for maximum savings and the heat pump takes a while to refresh a drained tank.  I estimate a typical 50 gallon unit has about 30 minutes of showering before it’s drained and that can be tight if you need back-to-back showers, or especially if you fill a tub then want to shower in the next hour.

Let me show you how I used the newest Rheem model in a novel way to solve this capacity issue.

I just completed a Lake House for clients who are nearing retirement.  Most of the time it’s just two people in the house, but since it’s a lake front house they get a huge influx of visitors on the summer weekends.  One normal tank wasn’t going to cut it for those weekends with guests.  Here’s my solution for an Ultimate Hot Water setup!

Two Rheem electric units. One Heat Pump & one super insulated tank for storage.

1  Rheem Hybrid Heat Pump 50 Gallon Electric


1 Rheem Marathon 50 Gallon Electric

= 100 gallons of standing hot water plus both units have electric resistance backups if you really had a big need for hot water and didn’t want to wait for the heat pump to cycle!

Here’s the setup:  The Heat Pump water heater is first to get the water from the outside.  It is set for Heat Pump Only Mode.

Hybrid Heat Pump unit is set to Heat Pump only mode for Maximum efficiency.

Then, the Rheem Marathon 50 Gallon tank is next in line.  It’s basically being used as a storage tank.  I really like the Marathon unit because it’s a super-insulated “Yeti Cooler” due to it’s 2.5″ of Polyurethane foam.  The Marathon is so well insulated it only loses 5 deg F over a 24 hour period!  The Marathon is getting 120 water from the Hybrid Heat Pump Water Heater so it will rar

The Heat Pump water heater outputs cold & dehumidified air so we used a Panasonic fan mounted behind it to move this cold air into the Laundry room behind this mechanical room.  The black tanks on the left are a Reverse Osmosis system to filter lake water.


Why this works:

1. The Rheem Hybrid unit when operating on Heat Pump only mode is super efficient.  It has an EF rating of 2.4, which means it’s 240% more efficient than a standard resistance electric heater!  But the down side is that the recovery time isn’t particularly fast.  That’s where the Marathon tank is necessary.  We now basically have a 100 gallon Heat Pump water heater that has 2 backup electric resistance elements!

2.  This combo also means that we don’t have to run a costly gas line (or maintain a propane tank), plus we don’t need to poke a hole in our roof for the vent!  Both of these mean less penetrations in my envelope and a reduction in the possibility of air or water leaks.

3.  The byproduct of the running the Heat Pump water heater is cool / dehumidified air!  We installed a pass through vent to the laundry room behind, then used a 50 cfm Panasonic vent fan with a 24 hour timer to periodically move the cold air out of this closet into our house (this closet is inside the thermal envelope).

4.  Redundancy!  I love that we have some redundancy in our system.  If one unit fails, the other can do the water heating until it gets serviced.  This is always a plus when you are a builder who is striving for an impeccable service reputation.

I wish you the Best in your #BUILD!

-Matt Risinger

Risinger Homes in Austin, TX

Visit my Blog at www.MattRisinger.com

Risinger Homes is a custom builder and whole house remodeling contractor that specializes in Architect driven and fine craftsmanship work. We utilize an in-house carpentry staff and the latest building science research to build dramatically more efficient, healthy and durable homes.

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