by • August 18, 2015 • Reviews, Uncategorized, Water Heating & Plumbing & ToiletsComments (13)8649

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

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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  • Ryan Crouch

    Awesome Matt!!! I’ve wondered when someone was going to do this setup. I should have known you would be the first! By the way your blog is very, very costly to read. I’m getting a Yeti tumbler based on your recommendation and as soon as the new iPhone 6s comes out in September I’m finally going to upgrade my iPhone 4 just so I can get the Flir One. Not really what for considering I’m still an RN, but it will be a fun and educational device.

    • Ha! Thanks for reading and commenting Ryan. Best, Matt

  • Samuel Mortimer

    Hi Matt – Do you have any experience within in-line DHW systems using solar thermal as one of the components? Thoughts either way? As always, love your insight.

    • I’ve not done any solar thermal yet. I often do Solar for electric generation but haven’t found a good installer for solar hot. I think it’s harder to pencil out factoring in complexity and maintenance. Especially because we have terrific rebates from Austin Energy. Matt

  • Tripp Pankey

    I like to do the same type of setup except I install the storage tank on the other side of the house close to the users so less wait. Typically the HP close to the kitchen and the storage close to the Master. This means the kitchen won’t have the full capacity of both tanks, but that’s ok.
    In a spray foam house, I like to put the HP tank in the encapsulated attic IF the attic is big enough with enough volume to support the HP. I am in a cooling dominated climate. However, heat rises and the attic stays warm enough during the winter.

    • Tripp, Great idea. I’ve not done this, but the Marathon being electric could fit in lots of spaces. No venting needed. Best, Matt

  • greenbuildingindenver

    I did something very similar to this in a 20 unit apartment building. My fear was: what if 100 gallons were used in a short time? Then the Marathon would be full of cold water, and no amount of waiting would solve the problem. Of course, a small recirc pump could solve the problem, but I’m always against complexity.
    Well my fears never materialized, and I never got the complaint. I predict that your experience will be the same. It could be that once the hot water is run for a little while, the hot water rises quickly to the top of the Marathon, and the user sees hot water long before having to use up all 50 gallons of cold in the Marathon.

    • Thanks for commenting. Always great when you hear the worst DOESN’T happen! Matt

  • Brad Bailey

    Hi Mat. I installed the Rheem HP 50 in my home a year ago and it is fantastic. This week City code came by and wants me to raise the installation onto a platform for the garage installation. This unit is so tall that I really don’t want to do that! I suspect code was written for old heaters with bottom electrical hook up to prevent garage fumes from source of ignition? The Rheem has electrical hook up on top way above the ground level. Do I ask city for a code variance or just suck it up and do a full re-install

  • Seth Tezyk

    So based on what you did here I thought of an alternative that would be great for cold water inlet temperatures (up North), but also a way to get the best of both worlds here in the Austin area. Electric tankless water heaters now are available up to 36KW (EcoSmart and Stiebel), the main problems are they require major power coming to them 150 to 180 amps, which requires at least a 300 amp service coming in and flow is decreased based on inlet water temps. Why not use a hybrid like you presented here, except using a 50 gal stainless tanked traditional hot water heater (HTP/Westinghouse) to get the water temps up to 80 degrees when high demand is needed and/or very cold inlet water temps and let the tankless bring it the rest of the way up as needed. This allows both to operate at peak efficiency, built in redundancy and where the water inlet temps are higher like here in Austin, you can go with a less powerful tankless unit that you can use with now standard 200 amp service. What are your thoughts?

    • Very interesting! I don’t have any experience with Electric Tankless however. I wonder how this would do with high demand times & cold inlet temps? Also, how expensive are the electric tankless units? Appreciate the smart comments…Matt

      • Seth Tezyk

        The electric tankless are relatively affordable with the 36 KW EcoSmart (who’s parent company just got bought out by Rheem) is currently $621.85 on Amazon and it’s MSRP is $649. The Stiebel 36 KW is currently $849 on Amazon and it’s MSRP is $1,015. From my research the EcoSmart is a best buy in that it has nice build quality, lower flow trigger point and a lifetime warranty. The Stiebel is German built and has superior build quality and a 3 year warranty. I think at this price point considering what the electric geothermal units are going for it’s definitely worth a try.

  • Chris Petrillose

    I currently have a GE geospring 50 gallon hybrid. We are finding that it is not enough for our family. What are you thoughts on using my current water heater along with 104 gallon Rheem Marathon in series like your setup?