Heat Pump Installation Tips

The single most important factor in heat pump installation is air flow. The unit must be placed where it can draw in a steady supply of fresh air and expel the cooled exhaust air without it recirculating back into the unit. Recirculation dramatically reduces efficiency and can cause the heat pump to overheat.

Horizontal fan models draw air in from the back and expel it from the front. Vertical fan models draw air in from the sides and blow it upwards out of the top.

Avoid positioning the heat pump where the expelled air will hit a fence, wall, hedge, or overhanging roof. These obstructions can cause the cool exhaust air to recirculate back into the intake, reducing performance significantly.

Every heat pump has a minimum water flow rate specified in its technical documentation. If the flow through the unit is too low, the water inside the heat exchanger will overheat and the safety system will shut the unit down.

Check the flow rate of your pool pump against the heat pump specifications before installation. If the pool pump is not powerful enough, or if the pipe run is very long, the flow may be insufficient. Fitting a flow meter to your pipework is the most reliable way to check this. Regularly backwashing the pool filter also helps maintain adequate flow over time.

The heat pump must sit on a level, solid base. Suitable options include a concrete pad, paving slabs laid on compacted sand, or timber decking. The unit should be raised slightly off the ground to allow condensate water to drain freely.

During operation, heat pumps produce condensation water, particularly in humid conditions. If the unit sits on decking, drill drainage holes below the unit to prevent water pooling and timber rot. Some models include a condensate outlet tube — a short length of hose can be attached to direct the water away from the base area.

Mounting feet and lightweight paving slabs are available from The Wooden Pool Store if needed.

Before purchasing a heat pump, confirm that the electrical supply at your property is capable of supporting the unit's running and startup currents. These figures are listed on the product specification.

Most installations will require a dedicated cable run back to the consumer unit and a dedicated circuit breaker. Heat pumps draw a brief spike of current when the compressor starts — to accommodate this without tripping the breaker, a Type D circuit breaker is normally recommended.

All electrical work should be completed by a qualified electrician who can also calculate the correct cable size for the length of the run. A longer cable requires a thicker conductor to compensate for increased resistance.

Adding a heat pump to an existing pool circuit is straightforward. The unit has two connections: an inlet (water in) and an outlet (water out). Before ordering any fittings, check the size of your existing pipes — in the UK, 1.5" is most common; in Europe, 50 mm is standard. Do not measure the external diameter to determine pipe size; check the markings stamped on the pipe or fittings instead.

The heat pump should be the last item in the flow circuit before the water returns to the pool, with one exception: if a chlorine dosing unit is fitted, it should come after the heat pump to prevent concentrated chlorine from passing through the heat exchanger.

A bypass arrangement using three valves is strongly recommended. This allows the heat pump to be isolated for maintenance or winter draining, and also allows the water flow rate through the unit to be adjusted. The bypass is particularly useful in winter when the heat pump needs to be drained to prevent frost damage to the heat exchanger.

If an existing gas or oil boiler is in place, leave it connected. Plumb the heat pump before the boiler so that the heat pump does most of the work, with the boiler set to a lower temperature as a top-up or backup.

Heat pumps work best outdoors with unrestricted access to fresh air. However, some models can be installed inside a plant room if the exhaust air is ducted outside through the wall. Vertical fan models can use ducting to route the expelled air out through the wall; horizontal fan models can be positioned against the wall with a hole cut through to the outside.

For any indoor installation, a ventilation grille or door vent must be installed on the opposite side of the room to allow fresh air to enter at the same rate that the heat pump expels it. Without this, the unit will recirculate the same increasingly cold air and its performance will fall rapidly.

Water must never be allowed to freeze inside the heat pump, as this can crack the heat exchanger and is not covered by the manufacturer's warranty. In winter, the bypass valves should be used to drain water from the heat pump completely, or a frost thermostat should be set up to keep the pool pump circulating water whenever the air temperature drops close to freezing.

Winter covers are available for most heat pump models to provide additional protection during extended periods of cold weather.