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How To Build a Off Grid Solar Hot Water Heater


This is a Solar hot water Batch Type pre-heater that pre-heats the water for my hot water tank inside the house. Cost $45.00 to build. I made it out of garage sale and Goodwill items and scrap wood I had laying around. It has been heating water up to 140 degrees and circulates thru the tank by natural flow no pump needed as it is lower than the main tank.




This is what it looked like when I finished. I added extra insulation and foamed all the cracks.

Step 2: Parts and pieces

This is a fresh water tank from an old camper trailer that was given to me. This project can be scaled up or down to suit your needs.

Step 3:


A piece of old peg board, A sheet of masonite would have worked better but this is what I had.

Step 4:

Cut frames and sides from scrap plywood. This is not the true curve but it is what I had for material.


Step 5:

3 pieces of .50 cent glass. Foil backed styrofoam board ends scrap from a garage remodel.

Step 6:

Tank painted .96 cent Wall Mart black. 99 cent space blanket glued to the peg board.

Step 7:

Box with glass added. Not attached yet, time to start plumbing.

Step 8:

I ran the hoses inside some old PVC, wrapped in strips of old foam bed pads for insulation. I put 2 valves in case I have to drain the outside system if it gets too cold this winter.

Step 9:

Built a box around the fittings, with an access hole to reach shut-offs. I’m making a small garden box under pipes.

Step 10:

Added another 1/2 inch of foil backed insulation and painted to match skirting. Sealed all the cracks with silacone sealant.

Step 11:

Cover for back of tank. I plumbed in a temp. meter from a car that tells me the temp. of the water in the top of the tank. I can see it and an outside temp. from in the house.

Step 12:

110 degrees at 9:30 AM. Not bad for a junk yard heater!

Step 13:

This is a new system I have been working on, It heats a 40 gallon tank under the bathroom floor that radiates heat thru the floor all night. So far it has been working great, it has warmed the tank to 120 degrees on a nice day. I will post a new instructable on this one later, when I have a few stats on it. I will be draining the system and filling with R.V. antifreeze soon.

Step 14:

Here is a rough drawing of how I plumbed it but most applications are different depending on the tank etc. always use pressure hose and have a pressure relief valve. Sorry about the drawing I’ll try it again later.

Step 15: winter testing

Snowy morning in Washington. Made it to 110 before noon. Outside temperature got up to 55. It reached 130 in the hottest part of the day. I think the reflection off the snow helped raise the temp. today. The last picture is all my experiments. In front is a small solar panel I made out of 20 broken garden lights. I will start an instructable on it next week to enter that contest for the laser cutter. Next is a solar water panel that heats a 50 gal tank under the bathroom floor and radiates heat out all night. Behind that is this instructable, behind that is my solar oven.
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