Heating your pond with the home central heating system.
Although a stand alone boiler specifically to heat your pond is without doubt the best method, it is possible to heat your pond from your home central heating system. A boiler with spare capacity (oversized for the house) is bonus, but not absolutely necessary as will be described later.
A diagram below shows the general layout, although this may change with different boilers. First it must be understood that the boiler must remain switched on at all times, so the pond can call for heat as and when is necessary. There are a couple of methods to achieve this, one is to leave the heating on at all times and control room temperatures with radiators thermostats (this is the simplest method). The other is to rewire the boiler control (electrician necessary) so that the boiler remains live even when switched of by the time clock. This is how my own is setup and required moving one wire only on the connection panel (though this may change with different models).
The point at which you 'Tee' off of the boiler is important, reasons for this are that many boilers have a zone valve fitted, that will give priority to the domestic hot water supply for the taps. (a zone valve is a motorized valve that opens and shuts the supply as demanded. Operated by the control panel). The Tee off point should be before any zone valve fitted within the boiler. If the point marked 1 on the diagram is used it is often unnecessary to fit an extra circulation pump to the pond heating, though it is then necessary to wire the pump to a permanent live connection in the control panel. If position 2 is chosen, it will then be necessary to fit another circulation pump on the pond line, this pump would be wired to the same connection within the digistat as the pond zone valve and positioned in the area marked 3.
A zone valve is required on the pond heating circuit, this is opened and closed by the digistat. When the pond sensor reads that the pond water requires heating it powers the zone valve and opens the hot water flow, which then circulates through the heat exchanger and warms the pond water.
It is some times easier to break into the central heating system somewhere within the house away from the boiler. If this route is taken always 'Tee' into a 22mm pipe if at all possible and make your pipe run to the pond in 22mm, this reduces friction within the pipe. This said it is possible to use 15mm pipe, but if long pipe runs are in order flow will be restricted. If breaking into the pipe work from the house and not the boiler it is necessary to fit radiator thermostats and leave the central heating switched on at all time. Pipe runs are often under the floor boards, two pipes running along side each other, one is the feed pipe, the other is the return. Remember the feed is taken from the hottest pipe and returned to the cooler one.
If your home central heating boiler is only large enough to run the radiators within your home, it is possible to still utilized the boiler to heat your pond. The connections are just as above, but if a timer is used on the digistat it can be operated when your home does not require the use of the boiler, for example; if your life style is such that you wake at 6.00am and go to work at 8.00am, arrive home at 5.30pm and go to bed at 11.00pm, you could set the timer to come on at 8.15am till 5.00pm, off till 11.15pm and on till 5.30am. More than enough heating time and you are still warm while at home. In a worse case scenario, the heating could be on over night, with good insulation and pond covers and still maintain pond temperature.
Insulation is the key to successful pond heating and every pipe should be well lagged. If your house is a long way from the pond always run the heating pipe work to the pond, never unless very close pond pipe work to the boiler. It is far easier to lag 22mm copper or plastic pipe with domestically available pipe lagging than to have to lag long runs of 1 1/2" or 2" PVC pipes.
If you have a long run down the garden to the pond, the best method of insulation is to dig a channel say 200mm wide and 500mm deep. Build a series of plywood boxes 200mm x 200mm x sheet length. Lay the boxes in the bottom of the trench and run the pipe work through the center, keeping the two pipes apart. Fill the boxes with polystyrene packing chips and then screw a lid on, then back fill with soil. If you insulate well, long runs of pipe work are not a problem.
