N.Design Studio

Pond heating

Heating your pond

In Great Britain we have to put up with with some long cold winters, and even during a normal summer the pond temperatures only reach 70 degrees Farenheit for short periods as we do have cool evenings. For this reason many Koi Keepers in this country have fitted a heater to their ponds.
For many years the most popular heater used in this country was swimming pool heaters made by a Canadian company, but these have now lost popularity as those previously used did not have stainless steel heat exchangers and there has been some concern amongst koi keepers that the copper and other non ferrous materials in the heat exchangers could leak into the pond water and cause serious problems with the fish.
Several members in South Wales have decided to use domestic gas boilers and a stainless steel heat exchanger.
A typical layout for this is shown below, and this page gives a general description of the components we use in Great Britain.
[Heater line drawing]

The description below gives a break down of these components and a description of each of the items used. In other countries you will obviously have different items and manufacturers.

 

[Keith's heater]BOILER

This photo is the general layout of one of these systems. The boiler is shown without the external casing, but the gas board say the casing must be fitted when the boiler is in use.
It can be any type of boiler, and either wall mounted or free standing, and it can have a balanced flue or a standard flue.
In the UK most people find it cheaper to use gas, but the boiler could also be oil fired. It is better to use the standard type of boiler instead of a combi boiler or similar.

A boiler with a cast iron heater exchanger is preferable, and do not go for a boiler with a low water content.
 

heat exchangerHEAT EXCHANGER

The stainless steel heater exchanger is the type used for heating swimming pools, and they are available in several sizes. The governing fact regarding the size required is usually the maximum pumping rate of the pumped pond water as stated by the manufacturers. For a pond of 5,000 gallons most dealers seem to recommend the 170,000 btu size. This has a maximum pond pump rate of 2,460 gals/hour.
For larger ponds there is a 230,000 btu model, and this is rated at 3,300 gals/hour. A pond of say 12,000 gallons would use a unit that is rated at 450,000 btu.

Expansion chamberEXPANSION CHAMBER

With a normal household system there is a small header tank in the attic which pressurises the system. It has to be at least one metre above the top of the boiler, and in a frost free position. This is not always possible in these systems and if there is not room for a header tank then an expansion chamber is used, and this keeps the system pressurised. The photograph shows the actual red expansion chamber, and also the kit which contains the pressure guage & safety valve, the flexible hose, and the fixing kit.

System pumpSYSTEM PUMP

A domestic central heating circulator is required to pump the heated water aroun the system, and through the heat exchanger. A popular choice is Grundfoss UPS 15/60, but there are many similar types on the market that could be used. On the lowest of the three settings which is all that is required, the pump delivers 200 gals/min and consumes 45 watts per hour.
Valves are positioned each side of the pump for easy maintenance.
 

ThermostatTHERMOSTAT

The thermostat is used to control the boiler, and so keep the temperature at the required temperature in the same way as a room thermostat keeps your home at the required temperature. The sensing bulb for the thermostat is positioned in the pocket built into the heat exchanger.


ThermostatThroughout the country there seems to be various ideas as to which is the best type of thermostat. It is necessary to have one that keeps the temperature within close limits, but does not mean that the boiler is always starting and stopping on its own internal thermostat.
Many members use a digital thermostat and there are several available now from large koi dealers.
The other popular thermostat used in the U.K. is the Honewell 675A controller. I use this one myself but many koi-keepers find this is not accurate enough, although it keeps my pond within one degree centigrade.

Boiler housingBOILER HOUSING

If you have an outhouse or other building close to the pond then the boiler can be housed there, but if there is nothing suitable then it will be necessary to construct a purpose built housing to protect it from the weather.
The photograph shown on the left is the one that Keith has built for his system. The top cover can be completely removed for easy access, and the open slatted louvre doors give good ventilation.
Other similar systems are also featured here.

See also how the heating system on a 6,000 gallon pond has been replaced using a gas central heating boiler.
This page gives a general idea of the system we have used in our club for heating our ponds, and in may be useful for other koi-keepers who live in colder climates.
FAQ Frequently asked questions about this system.
 

WARNING. Care must be taken when building a system such as this unless you are conversant with this type of work. If you are not qualified to do the wiring yourself then consult an electrician. In Great Britain it is a criminal offence to connect the gas system yourself, and this must be done by a CORGI registered fitter. If you are doing this in any other country then do get expert advice and make sure that all the installation and work confirms to local regulations.