Solar Hot Water

I recently finished the first phase of my solar hot water project and now get most of my domestic hot water from the sun.  Good times!

I followed the plan from BuildItSolar $1000 Solar Water Heater, modified to suit my situation and needs.

I wanted to do radiant floor heating on my ground floor so I have about 3 times the square footage of collector and a larger storage tank.


I built one panel almost exactly like the one from BuildItSolar, then while searching for keep copper pipe on craigslist (tip: do a search then click the rss icon in your url bar, which adds a rss feed of the search results to your feed reader or email client, at which point you see all the new results as they come in) and I found someone selling an old school set of commercial collectors.  There were three, 3’x8′, metal and glass collectors, model Colt Inc. C-141C (only identification on them) that were being used to heat an old hot tub.  Anyway the seller claimed they worked fine and didn’t leak – so at $200 bucks it was a good deal for me.  The three 3×8 panels give 72 sf and the 4×8 I built gives 32 sf, so I nominally have 104 sf of collector area.

Mounting the Collector

The collector is mounted on my carport roof.  4 pads of pressure treated 2×6 where put onto the roof with roofing compound and appropriately long lag bolts into the supporting beams of the roof.  A 4×4 was run from one end to the other as the base.  For my home built collector with it’s wooden frame I just used gate hinges to attach it to the 4×4 (replacing one of the screws with a lag bolt for extra support) The commercial collectors came on a piece of angle bar with some hinges that we managed to get to work with some slight fiddling.  I didn’t actually solder the three commercial collectors together, instead I spaced them apart by 8 inches and used hotwater discharge hose and hose clamps between them (with a little silicon caulk between the hose and the metal) so that if the collectors did have issues, or if I need to re-roof or do work up there it will be much easier to move the collectors. (Thus far it is working fine, zero leaks, but I’ll see how they hold up)  To raise the collectors up and down we came up with a cool solution of using 4 scaffold jacks with swivel bases.  The top end of the collectors are attached to a 4×4, and from there on each a scaffold jack has it’s base lag bolted to the 4×4 and the screw portion hangs down.  On the mounting pad another scaffold jack is attached with the screw portion pointing up – a piece of appropriately heavy pipe is put between them.  Each scaffold jack gives 18″ worth of movement, so total there is three feet worth of extension and all you have to do is turn the adjustment screws.  Worked out quite well and is easy to move up and down (though you have alternate legs every few inches of adjustment so as to not get things to cockeyed)



The tank is similar to the BuiltItSolar $1k tank, but a bit larger and I doubled up the 2x4s both top and bottom.  Used nail plates and several large nails through them.  For the lid I have tank liner, then 2″ insulation (which extends out over the 2×4) then 1/2″ plywood.  When I put in the tank insulation I made sure that it stuck up ever so slightly above the top of the tank, with the idea that that lid would rest on that – then I used long coated deck screws to tighten the lid down onto the tank, which seemed to cinch everything together nice and tight.  For the piping going into the tank I had it go between the lid and the tank edge insulation – I marked where it would be going through on the lid edge, then took off the lid and smashed the insulation down with a hammer, which just gave the piping enough space to fit in there (with the appropriate use of clamps and deck screws) so it seems like a real tight fit.  Nominally the exterior is 56″ x 48″ and this leads to a total of 213 gallons of storage capacity.  I also put 3″ foam I had laying around on the top of the lid and some of the left over 2″ foam around the sides of the tank.


The main heat exchanger is a 300′ loop of 1″ PEX, connected to the water system with CPVC for abut 6 feet of valves and elbows then to the copper line with sharkbite.  I did it that way to minimize install time as working with CPVC is really extremely easy vs trying to solder under the house up next to the joists and vents, etc.  I initially had the tie in come down from the ceiling and go in / out of the tank, but I noticed that at least on the outlet site I was leaking heat up the pipe pretty far, so I changed it so the tie in comes down from the ceiling to below the waterline in the tank then backup, this seems to prevent any convection from sending heat up the pipes.  I used a Wilo Star S 21BFX pump which seems to work well on the middle pump setting.  (The system has fairly high head as the collectors are on the carport roof and pump and tank are under my house) I used CPVC for the runs to and from the collector, again for the ease of use.  The outlet from the collector has about 15 feet of copper on it though.  I transition from copper to the CPVC using discharge hose and pipe clamps so that there will be some flexibility in the system when I change the angle.




I used a Thermal Leak Detector to check how the tank was doing thermally (seemed good and at $34 bucks those are handy to have around.)

For tank monitoring I have a La Crosse weather station, for which you can by an optional wireless sensor which includes a probe that will do up to 140 degrees F.   I dropped that in the tank and now I can tell you exactly what the tank temp is up in my office (114.6 after several partially cloudy and cloudy days.) I actually have my tank set to 150F, so it just stops at 140, but it’s good enough for me, as most of the time I use enough of the tank heat to keep it under 140.


The system seems to ‘flap’ a bit, where it will turn on to heat for a few minutes, then turn off, then a few minutes later turn on again.  If I had to guess I would say it has to do with sensor placement at the collector side, but I haven’t had a chance to play around with it yet.

There is a slight plastic smell to the water from the shower, seems to be slowly fading over time but it was a little annoying to me (my wife didn’t seem to notice)  I don’t know if that is the 300′ PEX, or the short run of CPVC and CPVC glue.


Still have the radiant heat flooring to put in.  I have all the pieces for that, just need to find some time this summer to do it.  I guess my one slight concern is the pump I have for it is a cheap iron circulation pump, and I was wondering if that will cause any problems other than just not lasting super long.  Guess I should hit up the internet and work that out.

5 thoughts on “Solar Hot Water

  1. Hi,

    Have you done any of the radiant infloor heating by solar yet? I am undertaking a huge project, and wanted some advice on your setup. Any pitfalls to watch out for, etc.

    I am planning to build a similar system with eight 4’x8′ collectors w/PEX pipe to heat water during the day; optimized for winter solar radiation, pleaced on my roof.
    It will have four; very heavily insulated, 500 gallon holding tanks for water, in the basement. Each tank will have a 300′ coil of 1″ PEX for my heat exchanger, giving me the equvalent of a 40 gallon hot water tank. The heated water from the tanks will also directly feed to my radiant infloor heating lines. There will be two, hotwater on demand unit also plumbed in. One to heat the tanks on cloudy days, the other to heat the DHW if neccesary.

    Thanks for your input.

  2. Eric
    Good job on the construction of the parallel flow collector and on the mounting. It looks very professional. Would like to see more details on the method of mounting and the storage system. Love your comment page. How did my make it?


    • Hi John, I added a couple more photos of the mounting, though I do have more photos as well as a number of sketches of plans for it somewhere. Been super busy.

      The comment page is part of “WordPress” which is the software I use to run the website. In general pretty good software, particularly for free. You can set up your own free blog on the website.

  3. Hi,

    I just picked up some Colt C-141c panels on Craigslist too . Did you take them apart and clean them or anything? Mine look a little cloudy so I’m wondering if that is normal or if the sealant out-gassed and formed a film on the inner surface that I should try to clean off… I’m thinking of coming off my collectors with PEX once I go through the roof since it’s rated at 200F. That pipe clamp connection between panels sounds like a great idea too.


    • Heya, I actually took the glass off one panel to look at it, not sure if I have any photos around of that but I’ll look. The cloudy seemed to be a bit just how the glass was, I can take a look at my mounted panels and see if I can tell anything but it seems like is just how they are. That said it wasn’t very hard to take the glass off. I stripped the old caulking and put in a new bead of black silicon when I put it back together – that is probably the hardest part since the original bead was probably done with a machine and is very clean. My attempted wasn’t quite so clean but seemed to work.

      I think if you do PEX to the collector you need to make sure it is totally blocked from UV or it deteriorates pretty fast (from what I remember reading) so you might want to search the web for PEX and UV and see what you would have to do. Also if you haven’t worked with PEX before it can be a real hassle to go around tight corners since it is hard to bend. I’ve only used it for my tank heat exchanger with 1″ PEX and it was challenge to bend for the inlet / outlet. Obviously that might not matter at all in your situation, just something to think about.

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