Permaflex looks like a promising tank liner. I'm also interested in hearing about some 'real-world' experience with it.

Why not go with XPS or other non-hygroscopic foam for the insulation? You wouldn't need to build a 2nd frame to hold the insulation and you avoid possible issues with water condensation in the cellulose.

Also, how will you be insulating the top and bottom of the tank?

Thanks for the write-up. I like seeing someone else's thought processes on a project like this.

Tim

any of the foams are going to be much more expensive for the same r value. also depending on the temperature you're going to run the tank at you may need to go polyiso as the others melt at a lot closer to solar hot water temps.

Since my tank will be in ground foam was the only option. I think I could get away with any of the foamboards but I found used polyiso on for real cheap and bought a bunch.

Strider is exactly right. The cellulose is quite a bit cheaper than rigid foam, and low cost is the reason why I'm using it. The frame will costvery little and be quite simple.

Directly under the 4x8 sheet of plywood for the tank, I'll be using multiple sheets of rigid foam. I know the first layer will be polyiso to take the heat, after that I'll go with whatever is cheaper which will probably be polystyrene.

The top will be similar to the bottom with at least one piece of rigid foam. I'm not exactly sure how the rest will be. I'm thinking I might make a frame and fill it with cellulose too, but we'll see.

can polystyrene handle the weight of the tank? I'm not sure but isn't that the white stuff with little beads? It compresses really easy compared to the pink or blue stuff which we put under slabs all the time.

They're actually both polystyrene. Expanded polystryene (eps) is the beady stuff, extruded polystryrene (xps) is the blue/pink foam. I'd be using xps. I forget the R value of EPS, but XPS is a fair amount better.

Have you considered using a freezer as the container?

Used freezers are a great (free) metal box with a nice white finished look, have decent insulation to start, and a hinged sealing lid.

The freezer can be enhanced by lining the inside with 1" rigid foam, and a one-piece EDPM liner, glued up above the water line, and a floating pool-blanket to reduce air convection loss.

Size can easily be in the 150-200 gallon range, which is fine for solar preheat. If your floor is cement, you could stack two, and have passive thermo-syphon heat the top tank.

There are liquid transport "totes" that hold 500 gallons, have a metal cage frame with a platic liner, and can be picked up cheap.

The only concern I have with a freezer is the plastics they use in them. I'm not sure what they use and how they'd hold up to very hot water. Same goes for the totes.

Trouble with those is that they don't fit through doors!

I had sort of the same issue working on my home graywater laundry to toilet system - I was limited by the accessway to my crawlspace.

With a "Built" water container, parts can be carried down through narrow basement stairs and assembled in place.

How's this coming along?

I haven't had any time to work on it. :)

I did measure out the area that it'll be going and I think its going to have to be a bit smaller than I had hoped. We'll see though.