Koi Pond Heater

Koi can live in a wide range of temperatures, from 34 to 90 degrees Fahrenheit.  However, the extreme temperature ranges aren't necessarily the best for their health and happiness.


The most harmful temperature range for Koi is from 40 to 50 degrees Fahrenheit. This is known by Koi enthusiasts as "Aeromonas Alley".  At this temperature range, Koi may be more susceptable to bacteria and parasites in the pond water.


With the Koi Pond Heating System, it is possible to pass through the "Aeromonas Alley" temperature range much more rapidly.  "Aeromonas Alley" may be skipped altogether, if you keep the pond temperature above 50 degrees Fahrenheit during fall, winter and spring.  We use energy efficient boilers on the Koi Pond Heater Systems, so operating costs are minimal.


For more information, read the FAQ.

Koi Pond Heater



External Koi Pond Heater


If your filter house isn't large enough to accommodate a boiler system or if your pond equipment isn't housed indoors, you can still use the Koi pond heater system.  We will install it a cabinet to keep it protected from the elements.


Windows to read the gauges.

All inputs and outputs come through
the bottom.

The front swings open to easily access
the components.



The Koi Pond Heating System can be used in a multitude of ways:

  • To maintain any temperature
  • To keep the pond from freezing
  • To heat the pond up for healing sick Koi


Recirculation Pump

How does it work?

Many Koi pond heaters pump water directly into the boiler.  We never pump pond water into a boiler.  Why? Debris and minerals from the pond water will build up in the boiler, reducing water flow and heater efficiency.  The boiler itself will then have to be repaired or replaced, costing time and money.  Boiler failure is the last thing you want to happen in January when the temperatures are sub-zero.

We use a closed-loop system with a heat exchanger. (It is much faster and far less costly to replace a heat exchanger than an entire boiler.)  The heat exchanger is made out of stainless steel. We do not use Copper heat exchangers (Copper is toxic to fish.)

We install the heat exchanger after the filter system.  The water passing through the unit should be as clean as possible.

The heater system installed on a bypass line.  It can be completely turned off in the summer when the water is warm, effectively doubling the life of the heat exchanger.



Simple Heater Schematic

This schematic shows how one of our simpler Koi pond heaters work.  More advanced systems include multiple heat exchangers, valves and return lines.  Click on the image to make it larger.



  1. Cold water flows towards the heat exchanger after it has passed through a filter system
  2. Valves for flow control regulate how much water goes to the heat exchanger
  3. The pond water temperature increases as it flows through the heat exchanger
  4. Boiler re-circulates glycol/water mix in a closed circuit
  5. Warm water returning to the pond



Maxi-Flow Heat Exchanger Features:

  • Constructed of high quality corrosion resistant stainless steel (AISI316) or Titanium
  • Rolled formed to shape and then precision welded
  • Specially designed built in flow restrictor to assure maximum heat exchange
  • Designed to minimize pressure loss in the heating system
  • Leak tested to assure that they are totally functional
  • Compact in size and require a minimum installation space - light weight
  • Significant energy savings
  • Available for all types of swimming pools, spas and hot tubs
  • Equipped with stainless steel holding brackets
Heat Exchanger



Koi pond heating systems are shippable!

We've taken a complete heater system and made it fit in within a standard sized pallet, so now we can ship them anywhere.  We pre-assemble as much of the unit as possible.  When we ship the heater system, the only work needed when it arrives is mounting the unit to a wall, hooking up the water input/output, attaching the gas line and connecting the electric.  See the pictures below.




For more information, email us at info@koiacres.com.