Larry Lunsford

If you've kept Koi for at least a year, you know how hard winter can be. Cold winter water slows down their activity and feeding. Fluctuating spring temperatures are rough on our living jewels. You can avoid these problems by heating your pond. Maybe you have already considered heating your pond, but you don't want to deal with the expense or difficulties of setting up some of the systems you have seen.

Here's a heating system that's inexpensive to buy and simple to install. The system consists of: water heater, pump, thermostat, valve, and heat pipe.

My home is heated by a radiant hot water system. I was able use my existing natural gas fired boiler as a heat source for my pond. This saved me from buying the most expensive part of the system. If your home water heater isn't big enough to handle the extra load, you can buy a second water heater for less than the cost of some of the pond heating systems.

I'm using a 100' coil of plastic pipe to transfer heat from my boiler to the pond. I simply put the pipe coil in my pond. You could also put the pipe in some area of your filter if you don't like looking at it in your pond. Use pipe intended for high pressure hot water. I got 100' of PEX pipe for less than $25.

Use a circulating pump (the kind for home radiator systems) to circulate hot water through the heating coil.

I'm using the thermostat from Aquatic Eco-Systems VT500 aquarium heater. The thermostat on this heater is separate from the heating element and it can be used to switch any 120VAC device up to 500W. Instead of using the thermostat to turn a heating element on and off, I'm using it to control the flow of hot water.

Most systems switch the circulating pump on and off to control heat. I've set up my system a little differently. I leave the circulating pump running constantly. To control the flow of heat, I switch a lawn sprinkler valve on and off. I also have a small pipe and needle valve that bypasses the sprinkler valve. The bypass allows a small flow of hot water at all times. I did this to reduce the possibility of freezing pipes between the house and pond.

If you use a lawn sprinkler valve, be sure to put it on the cold side. It's not designed to handle hot water.

Here's a breakdown of the parts and cost: manual shutoff valves 2 @ $4, circulating pump $75, thermostat $55, heat pipe $25, sprinkler valve $15, transformer for sprinkler valve $15, misc fittings and pipe $25, total cost is less than $220. If you've looked at commercial systems, you may be wondering what I've left out to make a system for a fraction of the cost. Here's the differences:

Commercial: Weather proof housing, circulate pond water through heater requiring expensive stainless steel components, made just for ponds in low volumes which results in high cost, large capacity, neatly packaged.

Do-It-Yourself: Taps into home hot water (totally eliminating cost of heater) or uses second home water heater (much cheaper than pond specific heater), does not circulate pond water through heater (no need for stainless steel or problems of clogging from algae and pond debris), you have to handle more details of installation.

Here's some comparisons of energy sources (examples assume 100,000 BTU per day needed to keep pond warm):

Even with the huge rate increase for natural gas that occurred over the winter of 2000 - 2001, natural gas is still far cheaper than other energy options.

For the ultimate conditions for your Koi, keep the water at 72° F to 75° F year round (Koi are people too). Of course, this is an expensive approach to pond heating. To keep heating costs low, you can adopt a more conservative approach. The most common approach is to just heat during winter months. Another approach is to use heat to just take the bite out of winter cold and to moderate spring and fall temperature fluctuations. With this approach, you would use a little heat in the middle of winter to keep the water in the upper 40's to mid 50's. You would also use heat to keep cold spells in spring and fall from causing too large of temperature drops. Whichever approach you choose, your Koi will benefit from the warm water.