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My installation of a heat pump water heater

My installation of a heat pump water heaterTo save money, and save energy, I embarked upon the installation of a hot water heat pump system.  This energy saving water heater should cut our electric bill, at least the part that is for hot water and dehumidification, quite a bit.  Heating the hot water with a heat pump is an ideal solution for our basement.  Our basement almost always needs dehumidification, so for years, in three homes now, we have run a dehumidifier.  Dehumidifiers do cost quite a bit of money to run.  And heating hot water with electricity costs even more.  We both like to take long showers, but meanwhile the electric meter is going tick tick!  A heat pump hot water heater is just a dehumidifier split in half.  A dehumidifier has a coil to cool incoming air and make water condense on the cool coil.  Then the cool air is funneled back through the necessary hot coil reheating the air back to room temperature (actually a little hotter).  A hot water heat pump acts as a dehumidifier, and an air conditioner, and the hot coil is used to heat your hot water.  Wow, perfect for the Spring, Summer, and Fall; in the winter, well, you have to make adjustments.  Regardless of the season it still saves money, especially if you've already installed a heat pump to heat and air condition your house.

Please do not forget, across the nation they are starting to deregulate electric utilities.  GOOD LUCK with your bills when they do!  One reason I am going heat pump crazy.

Alternative configurations

If we only had installed an air conditioning system in our home we might have been able to add a "de-superheater" to heat our hot water more economically.  But to me, number one, this is a far more complicated solution.  I like simple sub-systems in my home that are relatively decoupled.  This free standing "heat pump" acting as a water heater, air conditioner, and dehumidifier provides me we a completely independent, low operating cost, water heating system without complicating the heat pump used to heat, and air condition, the rest of the house.  KISS!  (Please see my whole house heat pump installation article).

Heat pump water heaters review

I looked at several vendors of equipment, and I wanted to take advantage of the $300 energy tax credit you are entitled too. (Sorry not after 2007!).  I chose a Nyletherm unit.  A unit that I would say has a medium cost.  There is a cheaper, and less complicated, solution on the market but I had some concerns.  One concern is galvanic corrosion.  You typically are adding parts to an existing water heater, these parts must be carefully chosen so they do not produce corrosion.  I wrote Air Tap and never received any confirmation regarding potential corrosion issues.  Nyletherm has been around long enough that I was not too concerned.

air scavenging hot water outlet tubeThere is another problem with the Air Tap unit, at least with our old hot water tank.  The 30 gallon heater we had was a side supply unit and I believe it would not have functioned with the Air Tap's concept.  Also 30 gallons is on the small side.  These side supply units have, what I would call, a air scavenging hot water outlet tube.  To the right you can see this tube which is normally inside your side piped water heater.  This tube would be very close to the top of the water heater thereby removing almost all the trapped air.  These heaters are usually used in tight, space saving, locations.  The Air Tap unit requires that you insert copper tubing in your hot water heater's outlet pipe.  I can virtually guarantee I would not have been able to install the Air Tap heat pump copper heating coil into this tube successfully.  Finally Air Tap has changed hands as well.


Yet another advantage of doing this installation, at this time, was the likely need for a new water heater.  I have no complaints about our last water heater.  It was a 30 gallon Rheem Warrior unit and it serviced us well, remarkably well.  This unit was built for manufactured homes and I am sure it was meant to be low cost.  It only had a one year warranty and it was now eight years old.  Surprisingly with only 30 gallons of storage we really never had any problems with hot water shortages.  But one drawback of a heat pump water heater is recovery time.  The time it takes to reheat your hot water supply is longer!  The solution to this is a bigger hot water tank.  I chose and installed a new hot water heater with a 50 gallon capacity, and technically a 60 gallon hot water supply capacity.  Since the water heater starts reheating the incoming water almost as soon as you draw off hot water, the unit is capable of heating an extra 10 gallons before you run out.  50 gallons is a good bit of hot water.  Our new 50 gallon unit from Home Depot is marketed under the GE name, but, it is also a Rheem unit!  For the Nyletherm heat pump unit we could have even gone with an 80 gallon tank.  For some reason the Air Tap unit only recommended a fifty gallon tank.

So a major part of the "preparation" for the heat pump in our home was installing a completely new water heater.  You really should consider replacing an old hot water heater as preventative maintenance for your home.  Look in the picture above at the over pressure, over temperature, protective valve.  See all the crap that came out of it!  I am not even sure what it is.  You are supposed to exercise this valve occasionally, but it can be difficult if your original installer did an incomplete job.  You just do not want a hot water heater to fail, and, they will always fail while you are on vacation!  Everything in your basement could be ruined.  If you were away for a week, your well pump or water would run for that long too!  The damages could easily pay for a new water heater several times over.  They are  pretty easy to install and you can do a better job than many contractors by providing all the appropriate failure protection drainage piping.

Finally you can also add provisions in your system to facilitate maintenance of your new hot water heat pump. 

Unpacking and inspecting my new water heater.


The hole package The parts laid out
More parts detail The hot water heat pump unit

Top left is the unit as delivered by truck.  It is heavy!  And there are quite a few parts.  The parts kit is really quite complete and should facilitate most installations well.  Shown upper right is all the parts including the optional duct adapters and condensate pump.  Plenty of PEX tubing is provided as well as insulation for the tubing.  This is a 220 volt condensate pump and the kit provides a junction box (with fuses believe or not) to install to support the condensate pump.  I swapped the 220 volt pump with an identical 120 volt unit that was with my air whole house air conditioner/heat pump.  The HVAC system really should have come with a 220 volt pump.  I liked using a separate 120 outlet for the condensate pump for the hot water heat pump.  I may use this pump to handle hot water failure overflow also, giving my a redundant power supply should a water heater failure open the 220 volt breaker.  Finally, lower right, you see the Nyletherm unit itself.  The air inlet filter is in front.  There are plugs which would allow you to "plumb" the unit from either side.  I had not noted the potential use of these plugs until after I had installed the unit.  The manual does not mention these plugs as far as I can remember.

Installing the Hot Water Heat Pump

It looked a bit intimidating at first, but it really turned out not to be too difficult to do.  For me complicating things was installing a whole new water heater.  Here I choose flexible copper couplings and added a hot water outlet valve, which should never be turned off at the same time as the cold water inlet valve when the water heater is energized (turned on).  When I installed the 50 gallon water heater it took forever to drain the house pipes, so there would be no water present while soldering (sweating) in all the fittings.  With two valves the heater can be replaced quickly.  Yes I will have to do this again in 15 or 20 years (if I am still around).

My installation steps

I broke the project down into a few major steps.

  1. Install and test the 50 gallon water heater for two weeks.
  2. Physically mount the hot water heat pump.
  3. Rewire the water heater and heat pump and test in "Bypass Mode"
  4. Install the plumbing between water heater and heat pump.
  5. Install the condensate pump.
  6. I had to install safety drainage for the water heater tank itself.


I used Tapcon screws to mount wooden blocks on top of my basement's insulation as a mounting surface for the bracket provided by Nyletherm.  I am able to set my entire heat pump down on a chair even after installation, if need be, for easy service.  I will ultimately be drywalling this wall and will be able to set the Nyletherm unit aside during this process.

When you mount the unit make sure you plan what you intend to do with the cool exhaust, and intake air (if anything).  I have some exotic plans to make a garden vegetable cooler using a heat exchanger etc.  Make sure there is clearance for the plumbing coming out of the side of the unit.  I did not leave enough clearance and had to remount the unit.


Nyletherm's wiring diagram is really a schematic.  To me a wiring diagram should closely (very closely) represent the physical layout of the terminals and connections involved.  Nyletherm's drawings are proper schematics that certainly show the correct electrical wiring but not the actual physical layout of the terminals involved.  Read their manual carefully and you will have no problems.  I chose to install a junction box on the wall rather than on the tank.  Again this sort of decouples the installation.

Also I had a bit of trouble fishing the required extra wire into the hot water tank itself, but it was doable, it just took a while.

The electrical installation also replaces both thermostats in the water heater.  This adds an over temperature safety cutoff to the lower thermostat which now controls the heat pump.  This makes a lot of sense in that the Nyletherm unit could conceivably overheat the tank (I doubt it).  With this design the lower water heater element is available as a convenient backup should the Nyletherm unit need service.  The Nyletherm unit has a standby switch which disables the heat pump and restores operation of the lower hot water heater element.  Also, if need be, it is trivial to electrically remove the Nyletherm unit from the system by moving one wire in the circuit.


hot water heater, a big wrench is needed to remove the drain tube.Be forewarned,  the water heater tank manufacturers really torque in the drain pipe.  Mine was very tight.  I needed a big wrench and some patient turning of the fitting to remove it.  I used Teflon tape on all the brass and galvanized fittings provided by Nyletherm.  I am delicate with my torque, so I ended up re-torquing a the fittings so there were no leaks.  Remember you can remove the valve handles if you have to.  Try to leave room so you can easily re-torque your fittings.  My water heater is in a tub which is elevated by concrete cap blocks.  This facilitates drainage if there are any failures in the water heater.

If you have a floor drain

This can be a great place for the condensate to go.  The hot water heat pump constantly produces condensate.  Many basement floor drains have "water traps" provided to prevent inflow and outflow of air (and perhaps radon) through the floor drain.  These floor drain traps need an almost continuous source of water or they DO NOT WORK!  The condensate is perfect for this.

Commissioning (Start Up)

I had already run the system in bypass mode, so once the plumbing was complete and flushed all I had to do was turn the unit to operational mode.  I was a little surprised, but it seems anytime after you cycle the circuit breaker to the system the Nyletherm unit seems to go through what I would guess is a defrost cycle running only the fan.  Only when there is demand from the thermostat, and this defrost cycle is complete, will the unit start heating.  If you have not allowed the lower element of the tank heater to preheat the water, the water running to the Nyletherm unit will be cold for a while and slowly come up to full temperature finally satisfying the lower thermostat on the water tank.

Our house has temperature balanced, and temperature limited, valves in the showers.  This allows for a slightly hotter safe setting of the water heater thermostats.  I am still not sure I understand the Nyletherm recommendation of having the upper element thermostat 5 degrees higher than the lower thermostat which now controls the heat pump.  Perhaps this is a quick recovery "comfort" setting, providing a little extra hot water, if there is excessive hot water usage.

Operational Problems

I only have one.  The variable speed fan in the unit must have a lose winding.  It makes an annoying hum when running; a hum that is louder than the well insulated compressor itself.  The compressor's sound is quite well muffled.  I cannot hear the pump at all, just the fan really, which is surprising.  I will be asking Nyletherm if the they will send my a new fan.

Other considerations

A tee in the outlet line plumbed to a valve then to the hot water outlet of the tank.  This would allow flushing air out of the Nyletherm just by turning one valve periodically.  This additional line requires insulation as well.


Well we have been taking showers, washing clothes, running the dishwasher, etc, everything's working fine, plenty of hot water.  I will let you know about the electric energy savings.  During this entire project I did drain and refill, and even reheated, my water heater three times, wasting quite a bit of electricity I am sure.  But I broke the project into pieces so I did not try to do too much at once.

I hope this helps you choose a heat pump water heater and hopefully it will facilitate your installation as well.  As I remember more details I will try to update this article.










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