DIY Backyard Greenhouse Aquaponics Project - Solar Heater

DIY Backyard Greenhouse Aquaponics Project – Solar Heater

As I talked about in my series on the DIY Backyard Greenhouse Aquaponics Project, I wanted to add a solar water heater to the fish tank.

Like the venturi aerator build, this was a very easy inexpensive project, and didn’t take much time to complete.

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I knew I needed a way to heat my water during the winter.

Most people just use electric or gas heaters, which can cost quite a bit during a cold winter, but I wanted a less expensive option.

I thought there had to be a way to do solar water heating for an aquaponics system.

Looking on the Internet I didn’t find a lot of good info on a robust DIY system.

I found a few YT videos on this, but they weren’t using it outside during the winter, only during spring startup.

Winter operation was my concern, and nothing I found really dealt with the freezing problems.

Solar water heater

Aquaponics solar water heat fish tank overall

Then I found the Build It Solar site, which has tons of great free DIY info on solar projects.

They have a drainback-style domestic solar water heater project that didn’t use antifreeze (glycol), and had a simple control mechanism.

Drainback is important where you are using water directly without antifreeze and may have freezing temperatures, which we are and will have.

This system they show you how to build is comparable to commercial systems costing 4 to 6 times as much.

I’ve worked for a solar company and installed a closed-loop glycol hot water system with separate heat-exchanger tank.

So I knew how much of a pain it is to work on. The DIY system Build It Solar created is much simpler, cheaper, and easier to install.

For my application, here’s the construction overview:

  1. Run a length of PEX-AL-PEX or copper line back and forth through a shallow box faced with glass or polycarbonate – called a collector
  2. Spray paint everything inside the box flat black (except glass)
  3. Tee off the pump supply water through it
  4. Adjust the flow valve until the water coming back is warm enough

For a house water heating, there’s a few more controls than that, but not much.

Overhead aquaponics solar heater pipe

In the future I will build it properly with the collector box and glazing, but I’m project-ed out right now.

So for the mean time, I have uncoiled 1/2″ irrigation tubing set inside at the front of the greenhouse.

This is not nearly as efficient as it would be in the glazed box method. But it was still able to heat water on a sunny day.

I also don’t like using this poly pipe for hot water. For now about 65°F it’s not a huge concern, but I’m not sure what will leach out when the water gets really hot.

Update: I put the pipe overhead to allow a better drainback and solar exposure. Then I realized that the pump wasn’t pushing the water up that high. Oops!

So I moved it down in front of the greenhouse, running it back and forth to allow maximum sun exposure.

This worked better, and the water was able to pass through to warm correctly.

Parts list

Here’s the parts list, which is PVC unless otherwise noted:

  • 1″ Tee with threaded center port
  • 1″ to 1/2″ threaded reduced bushing
  • 3 x 1/2″ close nipple
  • 2 x 1/2″ threaded ball valve
  • 1/2″ threaded Tee
  • 1/2″ irrigation tubing adapter, male threaded to barb

The construction generally goes in order of this list.

Like in the venturi aerator construction, I bought most of my PVC fittings from Supply House. Though I have no affiliation with them, the prices and shipping have been good.

What I also liked is not having to go the store and search for the parts (or worse, ask the non-existent employees).

They had the lowest price for most of the fittings I was looking for (by less than half), as well as having fittings in-stock not normally found in big box stores.

For example, a 1″ ball valve that’s $5.36 at HD is $1.65 from Supply House. They also carry a 1-1/2″ to 1″ slip reducer for the Affnan-style siphon top and a 1-1/4″ barb to 1″ threaded adapter for my pump hose.

Buying these oddball fittings online was the only option, because no one in town has them.

The total for these parts from Supply House was $6.78 as of 3/18, though not included are the irrigation fitting and tubing I already had.

Construction and controls

Aquaponics solar water heater fish tank tee and flow valveNote: Make sure to use pipe tape on any threaded parts to seal against leaks and get the threads screwed in well. I also suggest dry-fitting everything first without glue. This keeps “oops” from happening quite so often.

I tapped off the pump flow with a 1″ tee, which flows through the top bar of the “Tee”.

Into the threaded port of the tee went the reducer bushing, followed by the 1/2″ close nipple and 1/2″ ball valve.

Next I screwed the second close nipple into the ball valve, then the 1/2″ threaded tee.

Aquaponics solar water heater fish tank drain valve and output

Out the bottom of that tee threads the third close nipple, then the third ball valve.

Into the last port of tee I installed the irrigation tubing adapter. Over this fitting goes the irrigation tubing, secure by a stainless hose clamp.

This system is controlled with the two 1/2″ ball valves. One allows flow through the system, and the other drains the line when the system is off.

They are supposed to be used as though interlocked, in that they are never both on or off at once.

Operation & performance

I turn the solar heater on in the morning then shut it off at night to avoid the danger of freezing.

For the limited time it’s been in use, I’ve seen it heat my fish tank water (just under 500 gallons) between 5 and 10°F on a sunny day.

I think this is quite good, especially considering the cost. Unfortunately it doesn’t heat very well when it’s overcast.

I would like to have temperature sensors and control the whole system with an Ardiuno or other programmable chip (Raspberry Pi, etc).

This would save me from having to manually turn the system on in the morning and off at night. It would also heat better by only pumping water when it’s warmer in the collector than the fish tank.

But that will have to wait for another day. I’ll update this page if/when the collector and control system is built.


This is a super-fast, cheap (less than $7) and easy project that could save you lots of money in heating your aquaponics fish tank water.



OK, that’s all folks! Do you have any questions or comments about aquaponics, sustainable homesteading, permaculture design or anything else? Ask your question down below and let’s talk! You can also use the contact form, or email me at info at thepermaculture dot life.

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