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Running and Heating a Swimming Pool in NZ

Along with our house in Miranda came a swimming pool, looks really nice in the estate agents photos, but with just two adults and no kids it is not very practicable. Given the choice we would have opted for a spa poll, much cheaper all round.

But we have got a pool, so apart from draining it and having a sunken barbecue area, I need to keep the water clean etc. In the garage of our house was a pool cover that had never been used, so out that came and put into service. The disadvantage of a pool cover is that it hides the water and so the aesthetics are reduced, but chlorine consumption and chemical use drops dramatically and the pool will retain its temperature especially over night. In fact in NZ a pool without a pool cover is not a goer unless you enjoy cold water.

The pool is 8* 3.3 * 1.3 (avg. depth) metres giving a pool capacity of around 36000 litres ( 1 Cubic metre = 1000 litres). The chlorine is generated by converting salt, i.e. a salty pool.

The running costs

First the theoretical costs of electricity to keep the pool up to scratch. The recommendations for running the pool are 8 hours per day in summer and 4 hours per day in winter or when not in use. I did a check on the pools power usage and it worked out at 2 kw per hour, therefore in summer, that's 16 KWH per day, 480 KWH per 30 day month, cost NZ$120 per month with electricity at 25cents per KWH before discounts 2012/2013.

There is no way I am going to pay out that sort of money for a white elephant, even though we have a 3Kw solar system feeding back into the grid, it would use up more than our average generation per month in summer.

I have found with a little experimentation and the pool cover on, that I can get away with about 1 hour to 1. 30 mins. per day and still keep the chlorine level up, if needed, I shock dose of 3ppm with a liquid chlorine, which you are supposed to do anyway, especially before we get a visit from the relatives and there offspring. I do run the pump when the pool is being used. Please note, even running the pump for such a short time, the water is lovely and clear, the pool sides are clean and I only vacuum once a month and no not need a pool robot cleaner. This may not be true if loads of kids are in and out all day.

In winter I switched off the pump system, as did the previous owners of the house. Last summer (2012) our first here, the circulation pump was noisy, but bearable. When the time to start up the system in September 2012, the pump had seized up, so switching off in winter is probably a bad idea. The pump is now replaced with a 1HP down from 1.5HP, so the running costs are a little lower, about 1.5 Kw per hour. I will set the time clock for about 15 mins. per day in winter. I do not worry about chemicals and water clarity in winter, it only takes a water clearing chemical a few hours to sparkle up the water and the chemicals with all need dosing up after winter.

A salt water generator creates sodium hydroxide as a disinfectant, i.e. the active ingredient in household bleach. Therefore one can use bleach to super chlorinate your pool. It can work out cheaper than getting liquid chlor from your supplier, just do the sums. Bleach is 4.2% sodium hydroxide, most liquid chlors are 13% so you need 3 times the amount. Beware of Budget brand bleach, this is just 2.1%!

Heating the pool for New Zealand temperatures

In our first summer here, I went in the pool twice. The memshab went in more often, but she is better insulated than me. I suffer with a common English complaint of being “nesh”. This is an English Midlands expression meaning that you feel the cold! The summer of 2012 was the worst we have had in years, the result of a La Nina. The La Nina gave Aus. floods in place of bushfires. So 2012 was not the best years for pool swimming. Opening up the pool cover and replacing when the sun went in I managed to get the pool to a balmy 25 C. I am still not sure whether the pool heats up quicker with the pool cover on or not.

I decided, that if this bloody pool was to be used by me, heating was required. So first some calculations, please feel free to skip, if you have not fallen asleep by now!

It takes 4180 joules (watt second) to raise 1 litre of water 1 degree C

or 0.001161 KWH for the same.

The pool has a capacity of 36000 litres so requires 42.15 KWH to raise the pool 1 degree C.

So you need a lot of energy to first heat the pool and then keep it warm, even with a pool cover you will loose about 1.5 C per night.

There are three main ways of heating in NZ, electric heat pump, gas and solar.

Heating a pool with a heat pump

Pool heating with a heat pump costs, assuming a COP of 4 (1 KWH of electricity gives 4 KWH of heat), that's 6.25 cents per KWH, therefore NZ$2.62 per degree of temperature rise in my pool. Plus Plus you have to run the circulation pump to circulate the warm water, so another 25 to 50 cents per hour that the heating is running. I understand that if you are already running the circulation pump, these costs are not extra.

Cost: Approx $9000 incl. GST and Installation

Using Gas to heat a pool

I have done a little research into gas heating of a pool and come up with this blurb form a seller:

“A Pool that is heated on demand meets the needs of today's pool owner who seeks convenience and comfort in a busy life style. No-one wants to swim in a cold pool, but no-one wants to leave their pool heated when they are not using it either. Gas heating is the fastest way to heat a large volume of water; a correctly sized heater will put 12 degrees of heat into your swimming pool in a 24 hour period. This means the pool can be heated just for the school holidays, or even just for a weekend at surprising low cost. Unlike electric heating, a gas heater will continue to put the same amount of energy into your water regardless of the outside temperature. Ideal for those who want to use their pool whenever they want to, not just in the summer months. “Source:

Most NZ houses are not connected to gas and so LPG would be used for heating a pool, the current cost seems to be about 13 cents per KWH see:

The main advantage of using gas or electric to heat the pool is that you can use it all year round, I say advantage but even when we had a spa pool it only got used in the warmer months, those few yards to the bedroom from the pool always seem a long way!

Cost of heater: $7000 to $15000 incl. GST plus installation

Solar swimming pool heating

You have probably guessed that I have gone for solar heating. I have done a bit of research on various types, odd ones were discounted because I would have to run the circulation pump whilst there was a chance of the sun being out, which means all day again, one because I didn't like the politics of the country of origin, and so ended up with a local contractor who would adapt the system to my needs. To get around the all day running of the circulation pump, the intake pipe was run surface to the pool (to get around showing the pipe, I could have dug up some paving stones, but it was not a real problem) and the return was by of 2 of the 4 water inlets in the pool. The pipes took a tortuous route along by the fence up over the bedroom roof to the main roof area. The pool area is 28 metres squared, so is the solar collector area.

Does it work?

Yes, very well, the system was installed mid Oct. 2012, and the next day was nice and sunny, the pool went from 16C to 21C in the day, then dropped 1.5C overnight. This equates to input of 210 KWH equivalent, not bad.

The contractor set the switch off temperature to 31C, me thinking, that might be achievable in Jan/Feb, but no it got up there during late November. I have set the max. temp. now to 34C, I realise that's a bit warm, when the recommended for swimming is 26 to 27C, but it gives a buffer for cooler rainy days, anyway 27C still causes a sharp intake of breath when I venture in. 30C plus is a temp. one can idle about in. The chemical usage does not seem to be any higher so long as you keep the pool cover on, I have even found I do not need stabiliser, as that's required to offset UV.

So solar is free, well not quite, the system requires a 0.75HP pump, so about 15 cents per hour to run, (single phase motors are not that efficient).

Update March 25 2013: This summer has gone on and on, but apart from the lack of rain, temps. are around normal and the pool is still above 30 (just}. We dipped down to 28 following our 20 mms of rain, but bounced back again. That means we have been using the pool over six different months (not the same as six months use).

Update April 14 2013: Pool got to 30 today.

Update May 3 2013: April 15 was the last day we used the pool. The drought broke and we had a week of wettish weather. The pool has dropped to 22/23 and is too cold for me. I have left the solar on for 3 hours per day as just as an exercise, but this is really a waste of power.

Cost:$7200 all incl.

Contractor used:

Rick Flood

Pool Solar Heating Specialist Ltd

33 Landing Drive, Albany 0632

Mob 021-772-534 a/h 09-448-2522

Comparative costs of heating our pool

So I loose 1.5 degrees Centigrade over night in summer with the pool cover on, so how much to heat 36000 litres 1.5 C. Energy required is approx. 63 KWH

Electric Heat Pump (25 cents per KWH) 63 * 6.25 cents (COP 4) = NZ$3.93 per day, plus cost of running circulation pump.

Natural gas (10 cents per KWH) 63 * 10 = NZ$6.3 per day, plus cost of running circulation pump. (I took an average of some quoted prices please check accuracy.)

LPG (13 cents per KWH) 63 * 13 =NZ$8.19 per day plus circulation pump

Solar (assume pump running for 2.5 to 4 hours at 15 cents per hour, depending on suns strength) = 37.5 to 60 cents

A Must Have for your pool

A wireless pool temperature gauge. I searched for one in NZ and got nowhere, so Amazon it was. Amazon had a choice of 7 different models, but only 2 would ship to NZ. The one I bought works fine but would not receive through the wall, so the receiver is mounted adjacent to the window.

Note NZ post's Youshop gets around the problem of not having an US address, I now use it all the time.

The thermometer shown above failed, the transmission range got shorter (with new batteries), until it was no use. I bought this to replace the original one. Seems better built, much greater range, long term ???


I let the circulating pump and salt generator come on for 15 mins a day during the winter. This managed to keep the pool water clear.

Late Oct. 2013: I switched the controller on in early Oct. The pool got to the mid 20's by the 15th and has maintained between 24 and 27 for the rest of the month. I have been in a few times, but it really is a little cool for me.

Mid November, the pool is up to 34. The pool was used until mid April 2014, temperature kept above 30, then same as 2013, mid April, the drought broke and that was it until next October

Floatron swimming pool purifier

If you are thinking of using one of these for your pool, check out the price on before buying here (The NZ price seems a ripoff).

The NZ price is between 620 and 800 dollars NZ, using NZ Youshop, you could get one delivered to your door for around 370 NZ

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