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Solar Hot Water Heating (Simple; No Pumps or Electricity Needed)

Solar Hot Water Heater For Domestic Potable Water

After a lot of thinking about how much power I wasted by heating our water with Electricity or Propane, I came to the conclusion that it’s almost silly to not use the sun in the months where it’s readily available & staying above the freezing mark, which for us in North Idaho is generally a minimum of 7 months.

I initially spent a lot of time researching the issue and found that the solar hot water heaters available on the market were both expensive ($1,000 plus... & complex, from the perspective that you had to (A) use an electric pump & controller & (B) use a heat exchanger that was separated from the water you are heating. I didn’t want this, as a thousand bucks is too much PLUS I want it simple…

So, I bought a couple of the “How To Do It Yourself” instructional programs on building a hot water heater, and tried to learn from them. Here’s what I learned, and what really works.

First off, in the manuals they generally all came up with this idea that you use a reflective surface inside of the heat exchanger box to reflect sunlight & (heat?) back towards the actual heat exchangers. This is wrong, and doesn’t work. You want to ABSORB the heat inside of the box, but never reflect it. So, the idea is to paint the inside of the box black.

My primary concern was with the idea of if I would be able to heat ENOUGH water to supply my family or if I was just going to heat a small amount of water. I wanted to make the heat exchanger as large as possible, but still make it moveable, as it had to come apart & be moved in springtime. The other thing was that I wanted it to work through thermo siphon, (NO PUMPS, Ma!) so another consideration was the elevation relative to my hot water tank (more on this later).

The premise of Solar Hot Water Heating is simple; heat water and send it to a storage tank. I wanted to “one better” the plan, so I built mine using “Thermosiphon” to move the water for FREE!!!!

Below, I’ll show you how I built it, and how it works, plumbing, and thermosiphon:

Here’s a good link on how Thermosiphon works:

Here’s how I built mine:

I bought some Slant Fin Baseboard heat radiators, the simple kind you buy in your house to radiate hot water heat ( ). I bought these used, they were inexpensive, I think I paid $15.00 or so for all I needed. Then, bought some 3/8 inch glass, and (2) 12 foot 2x6’s, and another 6 foot 2x6, all treated. Together, for the heat exchanger, I think I have about $200 or so in it.

First, I built (2) small manifolds for the Slant Fin’s. These are simple, paralleled manifolds, one for the bottom (where water comes in) and one for the top (where water leaves & flows back to the hot water (Storage) tank). I installed these in “Parallel” so that when water comes into the bottom of the exchanger, it spreads out evenly across all 6 Slant Fins. The manifold at the bottom has a 45 degree angle on it for easier hookup.

                                                                                         Feed to Solar Hot Water Heater


After I made the manifolds, I soldered together the Slant Fins (they are ¾ inch copper), and connected them to the manifolds.

I made a box out of the treated lumber that measures 11 feet long & about 30 inches across, and installed the Slant Fins & Manifolds inside. Painted them black, and then installed the glass over the front.

I installed a thermometer inside (mistake…). You don’t want to do this; it will get hot enough inside later to destroy the thermometer.

Thermo siphon-

Thermosiphon has been used by mankind for millennia, it is an OLD way of moving water without pumping it.

Hot is lighter than cold, and the same applies to water.

You hook up the BOTTOM of your hot water TANK to the bottom of the solar hot water heater, ensuring that there is a drop of at least a couple of feet between your storage (hot water tank) and the Solar Hot Water Heater.

Then, install the Solar Hot Water Heater at an angle (doesn’t have to be anywhere near perfect) that is looking at the sun. 45 degrees maybe?

Last, install a return line FROM the Solar Hot Water Heater TO the hot water tank, arriving at the hot water tank at the TOP, and having an upwards climb of at least a foot between the two devices. Make SURE that there are no “droops” in the pipe. Install a one way “flapper” valve at the input side of the hot water tank, where your return line connects to the hot water tank, and install “bleeder” valves so that you can bleed the air out of the lines when you install turn on the system. Also, ensure that the “flapper” is positioned so that the “flapper” is hanging down inside of the valve. (It matters…) Get THIS valve, as it’s Brass, can withstand the heat, and will last....

Return from Solar Hot Water Heater
Return To Tank

Now, here’s how it works:

Like I said before, cold water is HEAVIER than warm water.

The cold water leaves the hot water storage tank, and goes into the Solar Hot Water Heater at the bottom. As soon as the sun hits the Solar Hot Water Heater, it heats the inside, and FAST!!! The water inside of the Slant Fins starts heating up, and in (literally) minutes, will rise in the Slant Fins to the top, and start circulating back into the top of the hot water tank.

The cold (HEAVY water will push the lighter hot water back into the top of the tank.

Water leaving the Hot Water Tank for the Solar Hot Water Heater leaves at about 55-60 degrees & returns at 120-130 degrees. It makes more than enough water to supply hot water for a family as long as the sun is out. When it gets colder outside, as long as it isn’t freezing weather, the Solar Hot Water heater will assist in warming up the water for you.

The best part is…..NO moving parts, no failures.


Output to Solar Hot Water Heater

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