Economical pool heating

Hi All,

I have a 10m x 4m pool and am thinking of installing heating for it but if I do, I want to do so reasonably cost-efficiently. I don't particularly have a preference for higher installation/lower running costs or v.v. What are your experiences/recommendations please?



HI John. The pool cleaner ran at night for about 2 hours with the filtration at the same time and I think the heating and filtration ran for about 6 hours during he day. When I started it all up in May I ran the heating for 24 hours a day for about 4 days to get it up to temp (85F as the girls liked it warm). All this from memory of course as I left the house in 2000. The water was nearly always gin clear while we used the pool. I kept the chlorine level quite high and shocked and flocced it with liquid chlorine when I opened up in mid May. The only time I vacuumed the pool bottom was when I opened up and removed the winter cover when the bottom was always pretty dirty. Otherwise I just skimmed off the leaves once or twice a week with a net.

Michael, how many hours did you run the filtration for? I think most owners are familiar with the fine dust cloud on the bottom of the pool. The one where as you commence cleaning the clear water turns slightly hazy so by the time you have finished the water has lost some of it's sparkle. the same as swimmers in the pool stirring up any really fine particles

Biggest difference in my pool is there is no dust or fine particles to cause any haziness to the water. Guests remarked with all 7 of them in the pool the water remained optically clear. They own a pool in the UK and asked me to look at theirs which I have done and the improvements are substantial both in the clarity and running costs.

Sorry John Edwards, bit of a thread creep but are you any closer to deciding how to heat your pool?

Interesting post John. We don't have a pool now and I don't have records of the costs of our one in UK. I recall I deduced the pool costs by comparing the consumption in the year before we installed it and after. I think we spent at least as much on chemicals as we did on heating.

Although I had a large filter and cleaned it regularly we still got quite a bit of dust and stuff on the bottom if I didn't use the cleaner. I don't recall the name but it had a couple of hoses that swept the bottom into a basket over the sump drain and collected a lot of stuff over about 7-10 days. It cost a lot (about £1500 as I recall) and had its own pump to run it.

Good posts!

It must be spring time and we are coming out of pool hibernation.

Michael, the reason the biggest cost is for running the pool pumps is simply because the pool industry is pretty (insert your own derogatory comment) The focus of my work on pools has been to address that very issue and I have installed a number of setups or adapted old ones where pumps etc have failed with the result of at least 90% saving in electricity.

In my own case, I sold my pool robot many seasons ago as it is not required. Pool robots simply put are expensive units that are used because the flow and filtration is not up to the job. All I have used for 3 seasons for the occasional leaf or four that miss the skimmer is a pool blaster max battery vacuum and I have a fair number of trees and hedging around my pool.

You make a good point on using gas for heating via an efficient condensing boiler/heat exchanger, I will have to take a look at bottled gas prices to get a feel of the cost, if you have any figures I would like to look over them?

The latest pool heat pumps are much more impressive than the older units as they have larger heat exchanger/collectors inverter controlled variable speed motors and produce in good conditions around 7.6 COP where older units may only be 4.6 COP.

On covers, all good fitting covers reduce heat loss to some degree but in cooler times when you want to retain heat a heat retaining foam cover works best. dark colours will increase heat loss over night and solar covers need to be clear to allow maximum solar gain when the sun is out. Dark coloured solar covers only cause the top couple of inches to get warm compared to the clear ones allowing the sun to warm much more of the water at depth.

Based on my experience over 10 years in UK I would not worry too much about the cost of heating the pool. The biggest cost is the electricity for the pumps especially if you include an automatic cleaner in the set-up. In France this will depend quite a bit on whether or not you have access to town gas or use LPG or oil in which case the arguments to a heat pump are better although the capital cost is still high in France. Maybe consider importing the heat pump from UK as prices are a lot lower. UK heating demand will be much higher than in France (unless in the North) so costs for actual heating will be lower than in UK.

We used to heat our pool from Mid May to mid-end September. I used a standard domestic condensing gas boiler with a heat exchanger and monitored the flow and return temperatures of the primary circuit closely as well as having an accurate thermostat on the secondary (pool water) circuit) which controlled the temperature to within about 0.5C. When you are heating this volume of water a small change equates to quite a lot of heat energy (i.e. joules or calories). At that time condensing boilers were just appearing on the domestic market,of course all domestic boilers are condensing now. I used a 70 BThU/Hr (20.5KwH)boiler to heat a pool slightly larger than your (12M x 5M) and it was fine apart from on very cold nights when it could only just cope. Most pool heaters are grossly over-specified (the one reccomended for our pool was 40KwH and of poor quality and inefficient. Using a domestic boiler with a good heat exchanger and accurate temperature control is a bit more expensive initially (in 1985 my system cost about £1500 against just under £1,000 for the "standard" US made pool boiler (both on parts only basis as I did the installation myself). It cost about 25% + more to run the pumps than the boiler. Don't forget that as the pool temperature increases the cost of chemicals will also rise as chlorine is broken down much faster as pool temp rises.

A good floating cover is essential as it will not only trap a lot of heat into the pool during sunny weather but will greatly reduce heat losses from the pool (evaporation is the greatest cause of heat loss from an open pool)

We reviewed a great many options and finally went with the air to water heat pump. Installed ourselves last year, was quite straightforward. Had to balance the wattage of the pump with the available electric supply so we went slightly small for our size of pool (same as yours.) Sorry but can't find a record of what size we installed and it's all wrapped up for the winter. Meant we had to accept it would need to run longer than a higher wattage one would to get same affect on water temperature.

Main advantage was the control. Heat pump means we can boost the pool temperature when we need to (that's when it's chilly/cloudy and cheaper solar systems don't work so well. When it's sunny our pool get's nice and warm anyway.

We find that if we run it overnight with air temperatures around 10° to 12° it lifts the water temp by around 2° to 3°. Using it every now and again when a cool day or rainfall chilled the pool we were able to swim right to the end of September and could have carried on except we were back in UK for some work. Becomes less efficient as air temperature drops, but night temperatures below 10°normally mean chillier days and no-one is clamouring for a swim anyway.

This year's investment will be a new pool cover to further improve heat retention overnight. The one we have came with the house when we bought it and is definitely past its best now.

Thanks John, much appreciated.

This is a tricky one, hopefully some others will give their input to but there are a fair number of variables.

If you go for a solar heating system then there are evacuated tubes which are really efficient, they use these for hot water in Antarctica

With evacuated tubes you can heat your pool and when not in use, say mid winter use the system for under floor heating. The only real downsides are in summer when the pool is up to temperature you have to find something to do with the available hot water so you obviously can heat your hot water tank but then what.

You need a fair amount of space for the tube arrays as well.

Forget rubber mats they just leak after a while.

There are various other polypropylene solar collectors which pump the pool water through them all quite simple but again you need quite an area to put them in (roughly 50% of the pools surface area) and they will cause some restriction in the water flow possibly increasing your electricity consumption as well. This depends on what height the panels are at. A friend of mine has his on the roof which is quite high so he increases the variable speed pump when the heating is required and that uses an additional 1275 watts per hour, another has them at ground level so no real issues there.

Then there is the air to water heat pump, these will work at the turn of the key whereas the above solar is only really effective when it warm outside and the sun is shining . Different for Evacuated tubes, they can work when it's cold but bright outside.

The heat pumps are like a fridge working in reverse, for a smaller amount of electricity say 2.5Kw you get a heat output of 10-12.5Kw as they use a fridge type setup to grab the warm air through a compressor into a heat exchanger to heat the water. Depending on the model some can work down to a temperature of -5 c although the performance will drop off drastically to maybe 5Kw as it gets colder. These pumps also have a smaller area required to site them but they are noisier than solar. It should be possible when not heating your pool to utilise the heat pump for underfloor heating as well but careful attention needs to be placed in the flow rate as pools generally use a high flow rate. The flow through the heat pump has only a minimal restriction on the pump so these can also be used on an ultra efficient Eco pool filtration/pump setup.

Not forgetting of course the need for a good cover to retain the heat you have in the pool. Insulating floor and walls of the pool structure is often overlooked and treated with a Gallic shrug but it works and can save 50% of the heating requirements of an insulated pool.