Homemade hot water tank from solar heating - best insulation

We are wanting to heat water with various means (solar, compost and rocket stove), and then to store it in a homemade tank to us for heating through hydronic radiators.  The question is, what is the best insulation for the tank?  The ones have have seen are a wooden box, plastic lining and polystyrene panel insulation.  I would rather not use the polystyrene for environmental reasons, but from what I have read, rockwool style insulation batts are not the best in terms of long-term quality, esp as it will be on the ground beside a pier and beam house in very damp New Zealand weather.

I have seen aircrete, but it is an expense to buy the initial equipment.  

Any other suggestions?

Can you rent the equipment, borrow from someone, or go in together to perhaps rent with someone nearby?

Perhaps a trade of goods or labor with someone that has the equipment necessary to do aircrete?

Our current 'thermal-bank' is made of old water-heaters plumbed in series. We got them free. They were already insulated and they take pressure.

If you're going to put foam in the ground, you will need that heavy stuff with the black material surface. It is an industrial product meant to last. I recently went back to some dense foam panels I had stacked on the ground and found them totally honeycombed with ants or termites.

This was verified recently when I  looked at a sprayed foam liner on a block house foundation and the inspector said code required a 2 inch gap between the foam which touched the ground and the wood of the house to prevent termites from getting into the wood.

Maybe foam sprayed with some sort of asphalt would work also.

I'm curious about the poor reports on rockwool,as it is said to be able to endure indefinite wet dry cycles.
A rainscreen should keep it dry.

This is one place where I read about the limitations of rockwool - though I know it is from a biased source:  http://www.domegaia.com/faq.html
I have read elsewhere that it will lose effectiveness when it sags in a vertical wall or as air goes through it etc.

I think in the USA that there needs to be some sort of air barrier between insulative batts and the outside.  here in New Zealand they just fit them under the house beams and run a few straps in place to hold them.  I can tell you with assurance that four years later they are all pulled out where my husband put them in.  Helped a bit by the dog and piglets going under there, but also wind and other animals.  Likewise, the bats are just laid above the ceiling between the bin beams with nothing to hold them in place.   When I went up to investigate a leak, a lot of them had been blown out of place.

We don't have to worry about termites in New Zealand, and only have a few small harmless ants.

I can't pull up any information about either individual or commerciall companies making aircrete or similar products in NZ from which I can hire equipment.  We do import panels from overseas which suggests we don't have our own factories.   I am considering buying plans to make my green dragon, and trying to get the products to make it second hand here, but then I still think we need the cement mixer thing.    

One option would be sawdust concrete, I don't know how it compares to aircrete for lightness and insulative effect.

What did you use to connect your water cyclinders?  Copper fittings is quite expensive here.

Thank you for sharing that site, I'll be pursuing it.
If there is Styrofoam waste near at hand,it could be used as aggregate in an insulative concrete.

Rockwool is pretty much fiberglass... or nuevo asbestos...

Rockwool is a hazardous material, there is no practical way to clean it up, especially from soil and installation exposes the workman, which exposes the laundry system and home. Cancer of the skin, lungs, digestive tract etc., it schwizzle sticks the nucleus of cells! Fun stuff and our homes are packed full of it, composite shingled roofs shed it constantly into air and water and it is constantly disturbed and rains almost microscopic particles indoors where it is inhaled and causes havoc in our cardio-pulmonary systems. Thanks industry!

Styrene is found in almost all human blood samples, propably from drinking vessels... coffee cups and those ridiculous party cups.

I removed all fiberglass from our cinder block and concrete home and was at the same issue with styrene as you are with your tank. We ruled out the best performer; poly spray foam because we saw extreme reports of people having to abandon their homes.

We did use styrene panels in the end as a temporary measure. The fire retardant chemicals are my main issue. They are known hormone disruptors. It is a vapor. We sealed it in its integral foil and mylar and hope for the best.

We also live in a very humid climate and have extreme temperatures, so insulation is a must.

Living in new zealand, could you use wool? It is moisture resistant, bug resistant except maybe moths, and insulates like any other batts. If you build a tight box on a riser to keep it out of the mud, cotton (or recycled denim) or wool batts could be kept well. As a positive, wool is natural, has no chemical additives and has good insulation properties even when damp.

The only problem i see with crete, air or foam mixed, is thickness. Airy or foamy concrete is still massive and conductive.

For a small project, wool is great, i doubt most people here or anywhere could afford a whole house insulated with wool. You could also skim coat it with clay or concrete to seal out bugs and mitigate moisture.

Our domestic hot water tank is a 48 gallon poly barrel (was for condiment food stuffs) and is insulated with multiple wraps of reflective double bubble. Works great minimal hazard or migration.

Check out Gary Reysa's DIY solar site: www.builtitsolar.com

Tons of stuff in there especially for DIY solar hot water heating.

Jason Durrie wrote:Check out Gary Reysa's DIY solar site: www.builtitsolar.com

Tons of stuff in there especially for DIY solar hot water heating.

Great suggestion. That is where the basic design for our water heater came from.