Solar hot water - Pre-heater

I have a perfectly good hot water service at home so I wont be throwing it away just yet. But I think I've decided on what I'll do instead. My plan is to make a pre-heater to heat the water that goes into my hot water service, so less energy is required to get my water up to temperature.

I already have a working understanding of heat exchange principles, so I'll leverage my new knowledge and attempt to apply it to pre-heating my hot water inlet. By doing so I'll avoid having to make a solar collector that is capable of taking mains (in in my house mains-like) water pressure.

Currently my hot water service takes delivery of its water at around 13 deg C and then uses fossil fuel to heat it to something like 65 deg C. If I can collect some heat and store it in an insulated container, I should be able to make a simple heat exchange device to transfer that heat to the inlet water of my hot water service. If I can spare my hot water service the trouble of even a few degrees It will have been worth it. But I'm hoping to contribute more like half the energy required to make my showers hot. If I can do that I can feel a bit more confident that I can make a replacement hot water service when my existing one gives up one day.

I guess that means my official target for my inlet water temperature is a 26 deg C increase from 13 deg C to 39 deg C.

That should be easy enough in summer but it's moving towards mid-winter here so I will be very pleased if I can get even close.


  1. Sounds good, have you checked how much heat solar set-ups put back into the atmosphere?

  2. Love the things you get up to. Have you looked at the Alternative Technology Association? I'm sure they'd enjoy your blog.

    1. I was just searching for something online and was sent here. But the result was that I noticed I seemed grumpy when I replied to your comment as well as Von's. So sorry, and thanks for the kind words :)

  3. Do solar setups put heat back into the atmosphere?
    As far as I can tell they just move heat around.

    Any reflected light would have to be calculated against what would have happened if the setup wasn't there. I have no idea how to go about calculating that but I cant imagine it would be as environmentally damaging as say, my house.

    I suspect any less fossil fuel I burn can only be a good thing. I'm building this out of stuff that would end up as landfill so the carbon footprint of the project is the same as it was before the project.

  4. re: Alternative Technology Association

    I'll have a look.

  5. Von, I just re-read my reply.

    I sounded grumpy.

    I'm not grumpy :)


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