The cost of materials for the 500 gallon thermal storage tank:
|Plywood sides and bottom||4X8 ft sheets of 3/4 inch exterior plywood||4||$72|
|2X4 Framing||2X4 framing (about 10 8 ft studs)||10||$30|
|EPDM liner||40 mil EPDM 14 ft from a 12 ft wide roll
(with some left over for other projects)
|Glue, screws, nails, tension tie, ..||$20|
|Total for uninsulated tank (2)||$240|
(add this amount for each R10
worth of insulation)
|Insulation per R10||136 sqft||$136(1)|
Interesting to note that by the time you get up to R20 insulation, the insulation costs more than the tank.
(1) This is the cost of rigid foam board insulation per R10. If you want R20 double this, R30 triple it. Lower R values could be used for a tank located inside, or in milder climates. Higher R values for outdoor tanks in cold climates.
If you have the space, and the tank lives in an environment that will permit it, the cost of insulation can be reduced by using batt style insulation around the sides of the tank rather than rigid foam board.
(2) This same list of materials would make a tank up 730 gallons, just by making the sides 4 ft high instead of 3ft high to make use of the full sheets of plywood.