Bestway Flowclear 4kw Pool Heater - Any Advice?

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  Keplaffintech on 16/10/2025 - 16:21

  How big is your pool? 4kw might not even be able to keep a typical pool up to temp.

  • 

    team teri on 16/10/2025 - 17:13

    It is fairly small, it's one of the oval Bestway above ground pools.

    But thanks for asking, that forces me to I stop being lazy and actually do the numbers.

    16,000 litres, that's 16 million millilitres. To warm up 1 millilitre of water by 1 degree takes 1 calorie, or 4.2J. To warm up the whole pool by 1 degree then takes 4.2*16M = 67MJ.

    4kW, that's 4000W. Times 3600 seconds in an hour, that's 14.4 MWs = 14.4 MJ.

    Dividing 67 by 14.4: A little under 5 hours of runtime to warm the pool by 1 degree.

    Sounds like it would work. Run the thing 8 hours a day from surplus solar, get ~1.5 degrees higher pool temp. Do that every day and the effect will be cumulative. Some of that extra warmth will be lost due to higher heat losses from a steeper temperature gradient. Those losses will be very variable depending on air temperature and wind speeds. But still, enough extra energy input to make a significant difference early and late in the season.

    Btw: not trying to be annoying by spelling out my calculations. Just hoping someone double checks and finds any mistakes I might have made :-)

    • 

      Keplaffintech on 16/10/2025 - 19:10

      You have to also consider heat loss. That's a big sucker of energy. There are some good online calculators that will do the math for you.

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  Stealtho on 16/10/2025 - 18:20

  Our pool is 28c now, was 30c few days last week, Nth NSW. IMO if it’s not warm/hot weather don’t really feel like swimming enough to heat it.

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  Ocker on 16/10/2025 - 18:21

  Buy a pool cover as well as that wlll retain the water heat

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    team teri on 16/10/2025 - 18:38

    I got that already, and it works quite well. One of the blue bubble covers, heats water right underneath it up a lot. By combining with well timed pump run-times to mix in the hot water from the top with the cold water at the bottom, I get a nice gradient after a few sunny days in a row.

    The main problem in the last few weeks: once the cover is off, the warming stops dead. Over night the pool cools off, and it takes several hours to get that back. That means I only really enjoy using the pool in the afternoons - but with the sea breeze coming in, that makes getting out a fairly cold experience.

    If this heater allows me to take the cover off in the mornings, with a similar water temperature that I now only see in the late afternoon, that would add lots of good pool days to the early season. :-)

  • 

    Stealtho on 16/10/2025 - 19:29

    PITA those things are

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  Ocker on 16/10/2025 - 18:57

  I am located in suburban Melbourne
  Our in-ground pool is 8mx4m and we have a solar heating system for the pool, comprising of rubber panels on the garage roof.
  The solar normally raises the pool temperature by about 6c and I put the pool cover on at night.
  During the peak season or (say) late October-late March the pool will stay at a constant 30c
  The solar heater has a 1hp pump, which runs at about 1kWh for which I pay 20c per kWh., When needed the pump runs for only a couple of hours a day.

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  Shame on 16/10/2025 - 19:09

  26C is my preferred temp but each to their own.

  If you have kW to spare then other uses might be to mine bitcoin, dehumidify your house or air filter your house. Reasons…
  - I don't believe in bitcoin but if you have spare kW then why not?
  - Air filtration is great if you have hay fever and the reduction in dust helps with cleaning,
  - Dehumidification prevents mould growth- my bathroom has awful air flow and the only thing that worked was putting a dehumidifier in the bathroom and running it for 2 hours per day. I wonder if putting a dehumidifier in the roof would help prevent any roof leaks from rotting timber before I discovered it?

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  Stealtho on 16/10/2025 - 19:31

  I like 28c, 30 is good in mornings but not when gets hotter.

  • 

    team teri on 16/10/2025 - 21:39

    For a moment there I thought you'd given me an idea for a new product.

    Alas, it already exists. A unit that can cool as well as heat.

    Not in my budget unfortunately…

  • 

    HelpMeiCantSee on 17/10/2025 - 19:59

    Pfft. 60kL @33 deg is where it’s at! October through april :)

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  dtoovey on 19/10/2025 - 18:02

  I bought an older version Bestway with 3kW with an english plug. Converted to Oz power. Man it sucks juice and heating is very slow. Expect to run it night and day for 3-4 days to add 4-5 degrees. I have a 5x3 m above ground intex with pool cover. Reckon heat gets lost through pool walls if outside air temp too cold. Have you considered a heat pump? The bestway i have needs pairing with a pump. I needed to add a diverter so i can take water from an outlet and either run it through the heater/roof pads to the pool or just through the heater. I think mine cost $300 but that was likely 6 years ago and "grey" import having the british plug.

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    team teri on 19/10/2025 - 23:36

    Sounds like you have one of the resistive ones like this. The price you paid sounds like it could be.

    Yes, that one would use almost 3 times the electricity for only 60% of the heat output. The one I'm basing this post on is a heat pump.