I currently have a water boiler where the inlet water is about 6C (43F) while in my country the average temperature is 15C.

I want to use the outdoor temperature just warm the water instead of heating it before it reaches my boiler. 50-100L storage would be enough for me. I was thinking of just having a tank with an inlet or outlet. I still want to keep the original pressure.

Is this possible to make yourself or are there any complete solutions to buy? I google but could not find anything. My budget is probably around €200/$200.

  • 1
    What's the minimum temperature? The 'complete solution' to this is a ground source heat pump system, which isn't subject to frost in winter.
    – Tetsujin
    Commented Sep 11, 2022 at 7:34
  • Try googling "solar hot water". Available in every country, mandatory in some! Supplement with an electric immersion heater in the solar storage tank, or with your own boiler.
    – jay613
    Commented Sep 11, 2022 at 15:25
  • please ensure you have a solution when the outside temp is below 0
    – Tiger Guy
    Commented Sep 11, 2022 at 16:06

3 Answers 3


This is a standard solution with solar water heating, to use a pre-heat tank to then supply a gas, electric or oil boiler that then has to work less.

The inlet temperature limits for the boiler needs to be checked, some will do this with no issue and some boilers are designed to "pass-through" if the water is already sufficiently hot.

There are tanks designed for this so purchase a tank which will then not have any issues meeting building codes, water codes and insurance requirements.

  • This. Because a coil of anything by itself offers no storage, a tank by itself offers poor heating. Once you combine them, make them out of materials that meet building code, and add overheat and overpressure protection. ... IMO you arrive at this Answer. Solar water heating with storage plus supplemental heating either in the storage tank or in the house. IT's cheap, commercially available, and safe.
    – jay613
    Commented Sep 11, 2022 at 15:22

You need a pressure vessel large enough to hold your water, it might be best to start with a scrap metal dealer before becoming a boilermaker.

I immagine you could strip the insulation from a reguals hot-water storage-heater tank and use that.


There are cheepr more efective solutions.

Buy a coil of drip irigation hose (1/2 inch) 100 foot long.

Then without uncoiling it place in a sunny spot and connect to outdoor valve (for garden hose).

Connect the other end to your boiler, where you install a T juction with two valves so you can switch as needed.

The pressure will be the same as your water lines.

The temperature will surprise you, on a sunny day it will exceed the outside temperature.

  • 1
    And then cut the bottoms off empty clear plastic drinks bottles and thread them on the pipe - cheap easy insulation as it stops wind losses and contact with the ground.
    – Solar Mike
    Commented Sep 11, 2022 at 8:50
  • This is probably the best solution for the low price range. It will be manual in that the sun will take close to an hour to heat the water each time.
    – crip659
    Commented Sep 11, 2022 at 10:22
  • 3
    Drip irrigation hose is not potable water rated, normally. It also has a relatively low pressure rating. Use black poly pipe that IS potable water rated.
    – Ecnerwal
    Commented Sep 11, 2022 at 12:03
  • I think a home's water supply needs something more robust than this. Irrigation hose, rubber hose parts, chopped up soda bottles. All it needs is a rusty old washing machine and a flux capacitor. :)
    – jay613
    Commented Sep 11, 2022 at 15:04
  • @jay613 it was a solution (temporary, first step, easy to implement) and was first done afaik in Australia where it was used to provide a sinkful of hot water for washing up, or bathing a kid. My mum used to put a metal bath full of water in the greenhouse in the summer and I would get a nice warm bath in the evening and that was in the UK...
    – Solar Mike
    Commented Sep 11, 2022 at 15:46

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.