What Is a Desuperheater?
A desuperheater is a small heat exchanger inside a geothermal heat pump that
grabs waste heat off the hot refrigerant line and sends it to your water heater. It makes hot water nearly
free while the system is already running for heating or cooling.
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It is the most underrated part of a geothermal system, and almost nobody around here brings it up. Most
homeowners with geothermal do not know their unit can heat their water, and a lot of them already own the
hardware to do it.
Where the free hot water comes from
When a heat pump is running, the refrigerant leaving the compressor is much hotter than it needs to be
for the job it is about to do. That extra heat, the superheat, normally gets thrown away. A desuperheater
is a second heat exchanger that intercepts some of it and moves it into your domestic hot water instead.
The important part: you are not running the compressor for the water. It is already running for your
heating or cooling. The hot water is a byproduct of work you were paying for anyway.
The best time for it is the middle of an Oklahoma summer. The system is running hard in cooling, it is
producing plenty of waste heat, and it would otherwise be dumping all of that into the ground. Instead a
chunk of it goes into your tank.
What it does not do, said plainly
A desuperheater is not a water heater. It supplements one. When your geothermal system is not running
much, in the mild stretches of spring and fall, it is not producing much surplus heat either, so your
regular water heater picks the load back up. Anyone telling you a desuperheater eliminates water heating
costs year round is overselling it.
What it does is take a real bite out of one of the larger loads in your house, for free, during the
months your system runs the most. That is worth having, and it is worth having installed correctly.
What it does to your wallet
The dollar version
Water heating is one of the biggest energy loads in a typical home, behind heating and cooling. A
desuperheater shifts part of that load onto heat you had already paid to move. There is no new compressor,
no new fuel, and no new monthly cost.
Many geothermal units, including the ClimateMaster GeoElite equipment I install most, come with the
desuperheater built in or available from the factory. In a lot of houses the unit already has it and it was
simply never connected. That is a comparatively small job with a permanent payoff.
The full installation detail, the dedicated geothermal water heating option, and the Oklahoma utility
rebate angle live on my
geothermal water heater and desuperheater
page.
What I check on an existing desuperheater
Whether it is connected at all, which is the first surprise on plenty of service calls. Then the pump,
the piping direction, the insulation on the lines, and whether the water heater’s own settings are fighting
it. A desuperheater plumbed backwards or left uninsulated quietly gives back most of what it earns.
It is one of the items in my Geothermal Diagnostic, $348 flat. That is a full performance audit: loop
pressure, refrigerant charge, desuperheater, controls, and heat exchanger, with a written report and a
quote before I leave. No credit, no refund, no money back.
Questions I get about this
Does a desuperheater really give you free hot water?
Nearly free, while the system is running. You are capturing heat you already paid to move, so there is no additional fuel and no additional compressor time. In the mild months when the system runs less, your normal water heater carries more of the load.
Does my geothermal unit already have a desuperheater?
Quite possibly. Many geothermal heat pumps ship with one built in or as a factory option, and I regularly find units where it was never connected to the water heater. It is worth checking before you buy anything.
Can a desuperheater be added to an existing geothermal system?
Often yes, depending on the unit. If the hardware is there, it is a matter of doing the water heater side and the piping correctly. If it is not, there are still options. Details are on my geothermal water heating page.
Will a desuperheater work in the winter too?
It works whenever the compressor is running, including heating season. It produces the most in cooling season, when the system is rejecting the most heat and would otherwise send all of it into the ground.
Is a desuperheater worth it in Oklahoma?
In a house with long cooling seasons, which is every house in this state, yes. The summers here are exactly the conditions where a desuperheater earns the most, because the system is running hard for months.
Keep going:
Want me to check whether yours is even hooked up?
If you already have geothermal, there is a real chance the desuperheater is sitting there unconnected. I will find out, along with everything else on the system, in the $348 Geothermal Diagnostic, and you get the written report before I leave.
Dave Hartzell, Hartzell's Heat & Air, 602 S Main St, Kingfisher, Oklahoma. Master HVAC License, NATE Certified, IGSHPA Accredited, ClimateMaster GeoElite. New system estimates are free anywhere in Oklahoma. Diagnosing an existing geothermal system is my $348 flat Geothermal Diagnostic, no credit and no refund, with a written report before I leave.