Pool heat pump running cost NZ: what each extra week of season costs
Nobody in New Zealand heats a swimming pool all year. What pool owners actually buy is season length - a few more weeks at each end of summer when the water is usable rather than merely present. That reframes the running-cost question entirely: not "what does it cost per month" but "what does another fortnight of swimming cost".
On a typical 1.8 kW pool heat pump running 6 hours a day, plus the filtration pump that has to run alongside it, the answer is about $46 a week.
Buying season by the week
An unheated New Zealand pool is comfortable for roughly twelve weeks around the peak of summer. Everything beyond that is heating you are paying for:
| Season | Weeks swimming | Weeks heated | Heating cost |
|---|---|---|---|
| Unheated - peak summer only | 12 | 0 | - |
| November to March | 18 | 6 | $275 |
| October to April | 26 | 14 | $642 |
| September to May | 34 | 22 | $1,009 |
Presented that way the decision becomes a normal household one: is another two months of swimming worth roughly $367? For a family that swims most days, easily. For a pool used at weekends, less obviously.
One caveat on the shoulders of the season: the further from summer you push, the harder the heat pump works for each degree, because it is drawing heat from cooler air and losing heat to a cooler night. Late-season weeks cost more than the flat weekly figure implies.
Why the heat pump is not the expensive part
A pool heat pump is the most efficient heat pump in a typical New Zealand home, and by a wide margin. A house heat pump has to lift air to 20°C in a Canterbury frost - a big temperature difference, and its coefficient of performance suffers accordingly. A pool heat pump is lifting water a few degrees, in spring, from air that is already mild. Under those conditions it commonly achieves a COP of five or more.
The practical consequence: the same heating done with a resistive element would cost around $596 a month instead of $119. If you have an old element-based pool heater, replacing it is one of the clearest efficiency wins available anywhere in a house.
The cover matters more than the heater
An uncovered pool loses most of its heat by evaporation off the surface. Every litre that evaporates carries away a large amount of energy, and it happens continuously, day and night, whether or not anyone is swimming.
A floating cover essentially stops that. Owners routinely find it halves their heating cost, and it has no running cost of its own - which makes it a better investment than any upgrade to the heater itself.
If you are being quoted for a pool heat pump right now, the sequence that saves the most money is: fit the cover first, run a season, then size the heater to whatever heating you still need. Sizing a heat pump for an uncovered pool means buying capacity to replace heat you could simply have stopped losing.
Run it in the daytime
Almost everything else on this site points towards shifting load to overnight. Pool heating is the exception, and for a good reason: the heat pump extracts warmth from the outside air, so its efficiency tracks the air temperature. Run at 2am in October it is working against the coldest air of the day.
- Heat pump: daytime, ideally through the warmest part of the afternoon.
- Filtration pump: shiftable. This one can go overnight if your plan has a cheaper night rate - see when power is cheapest in NZ. It just has to run enough hours in total to turn the water over.
- Do not run the heat pump without the filtration pump. It needs flow through it to work at all, which is why the two figures on this page belong together.
Sizing and siting
- Undersizing costs more, not less. A unit too small for the pool runs continuously and never quite gets there, which is the worst of both worlds.
- Give it airflow. It needs a clear volume of air to draw from and somewhere to exhaust the cooled air. Boxed into a corner, it recycles its own cold output.
- Shelter the pool from wind. Wind across an uncovered surface accelerates evaporation dramatically. A fence or hedge on the prevailing side reduces heating demand permanently.
To model your own pool and season against your rate, open the calculator. If you have a spa rather than a pool, the economics are quite different - a spa is held hot year-round, and that page covers it.