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Efficient Koi Water Heating Using Your Gas Water Heater By Larry Lunsford
This article was written by Larry Lunsford and appeared in the Mid Atlantic Koi Club Newsletter. If you are not in MAKC you should join now and be a part of one of the USA's largest and BEST clubs.
Introduction:
Many Koi keepers, especially the more Koi Kichi, have ponds that they want to heat. The simplest approach is to use electric heat. Electric heat is ok for small ponds or for temporary use, but the expense can get to be too much for larger ponds or for long term use. In many parts of the country, natural gas is significantly cheaper than electricity. This article will show you how to use your gas water heater to heat your Koi pond and save some money on your electric bill.
The System:
The figure shows the parts you need and how they connect into your water heater to provide heat for your Koi pond. The system circulates water from the water heater, to a heat exchanger, and back to the water heater. Water from the heater and water from the pond never mix -they just get close enough to transfer heat. The heat exchanger can be put in a variety of places. The figure shows the heat exchanger in its own tank as a separate stage in the filter. Pond water is pumped to the heat exchange tank, flows over the heat exchange coil, and then flows into the filter. The heat exchanger should be completely submerged and in an area where there is a good flow of pond water moving across it.
Calculating Heat Requirements:
Before going further, you need to determine how much heat you want your system to provide. Gas water heaters are usually rated in BTUs per hour. One BTU is the amount of heat required to raise the temperature of 1 pound of water by I degree Fahrenheit. Typical gas water heaters are rated in the range of 30,000 to 60,000 BTUs per hour. You'll have to decide how much of your water heater's capacity you want to divert to your pond.
If you are currently using electric heat, then it is an easy matter to calculate the BTUs you need. The formula for converting watts to BTU is:
BTUs (per hour) = watts x duty cycle x 3.4118 The duty cycle is the amount of time that your electric heater is on. Example: you have a 500 watt electric heater that is on 2/3 of the time. The BTUs is 500 x .666 x 3.41~8 1137.
Another way to estimate BTU requirement is to use heat loss per day. The formula is BTUs (per hour) gallons x degrees x 8.36 (pounds of water per gallon) I 24 (hours per day)
Example: your pond is 2000 gallons and you have a heat loss of 15 degrees per day. BTUs required is 2000 x 15 x 8.36 I 24 = 10,450 BTUs per hour.
Determining how much heat your pond will require is difficult because every one is different. Once you know your BTU requirement, you can calculate the water flow needed. The formula for water flow is:
flow (gallons per hour) = BTUs (per hour) I temperature drop in exchanger I 8.36
Temperature Drop:
The temperature drop in the heat exchanger is the difference between the water temperature when it goes into the heat exchanger and its temperature when it comes out. Most water heaters will put out water that is 110 to 140 degrees. The temperature of the water when it leaves the heat exchanger will be close to the temperature of the pond. Example: you calculated your BTU requirement to be 2000 BTUs per hour; your temperature drop in the heat exchanger is 50 degrees; flow = 2000 I 501 8.36 = 4.78 gallons per hour (GPH).
The flow rates calculated above assume that your system is constantly running. If your system only runs part time, then it will have pump proportionately more water when it is running.
Constructing Your System:
To build your heating system, you will need the following materials:
Shutoff Valves (2)
Circulating Pump
Heat Exchanger
Flow Regulating Valve
Thermostat (optional)
Timer (optional)
Misc. Pipe and Fittings
The shutoff valves are used to isolate the system from the rest of the house water for servicing. The flow regulating valve is used to control the maximum flow rate of water through the system. This valve should be one of the multi-turn style so that you can precisely adjust the water flow. The heat exchanger is simply a length of pipe used to trade heat from the water from the heater to the water in the pond. You can buy a heat exchanger from companies such as Aquatic Eco Systems, or you can make your own. The heat exchanger should be made of something that can and water pressure of your water heater and is now . Suitable materials are stainless steel, titanium, plastic and aluminum. Cooper should be avoided since it is Koi and in some circumstances cooper could be dissolved into the pond water. Circulating pumps are available from plumbing supply stores. Select a pump that has adequate flow (you probably won’t need much) and is power efficient. I am using a pump from Laing that only uses 33 suitable thermostats are available from plumbing supply stores and aquaculture companies. The misc pipes and fittings need to match your existing plumbing and adapt to your heat exchanger. It’s ok to use copper here since it won’t come in contact with the pond.
The Thermostat is Optional:
If you do not use a thermostat, then you will have to control your pond temperature by adjusting the flow regulating valve or with the timer. If you do choose to use a thermostat, then you want one that can control 12OVAC and that has a suitable temperature range. It's best to place the temperature probe where the koi can't get at it. I've lost two digital thermometers to curious koi they pulled one into the pond and they pulled the probe off the other.
The timer is also optional. The timer is used to control when the pump is allowed to run (so you don't use all your hot water just before you want to take a shower). The demand on your water heater may be low enough that you do not need to block out any times. A simple timer like those used to automatically turn your lights on and off will work. You can use just a timer without a thermostat and control your pond heating by adjusting the amount of time the system runs.
Before you connect everything:
Before you connect everything to your pond and water heater, you need to do a flow rate test. The flow regulating valve is used to limit the amount of heat that the system can put in your Koi pond. It is used as a safety in case the timer or thermostat gets stuck on. Your water heater can probably provide a lot more heat than you want to put in your Koi pond. You want to make sure that you never have a mechanical failure that would harm your Koi. Set up your circulating pump, heat exchanger and flow regulating valve with a barrel of water. Measure the flow rates at several different valve settings and record the results for later use. You can determine your flow rate by measuring how long it takes to fill a bucket or jug of known size. To calculate your flow rate use the formula:
flow (GP H) = 60 x 60/time to fill bucket (in seconds) x bucket size (in gallons)
Example: It takes 2 mm 15 sec to fill a 1/2 gallon jug. The flow is 60 x 60/135 x .5 = 13.3 GPH.
You are now ready to install the system:
Hook up everything as shown. Test the system to make sure nothing leaks. Put insulation on the pipes from the water heater. Set the flow regulating valve so that it will allow a little more water through the system than you have calculated that you need, but not too much more. Watch the water temperature in the pond closely for several days until it has stabilized. Note how often the circulating pump is running. With the flow set close to the minimum, the pump should be on most of the time. Make changes in settings in slow increments. It will take a while for the temperature to stabilize after changing settings. Do not be concerned if you can't tell any difference in the temperature of the pond water before it gets to the heat exchanger vs. after flowing over the exchanger. The difference will be minute, but over many hours of continuous operation, the temperature of the pond will rise.
Filters that have not had water circulating through them for the winter should be cleaned well before turning the pump back on this spring. Cleaning will remove toxins that can develop from waste breaking down in the filter in the absence of oxygen. Once your filter is up and running, seed it with beneficial bacteria.
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