Since doing the concrete work, I had to redesign the tank to fit the new area. It is now based off a 4'x6' sheet of plywood base. The new tank will hold around 500 gallons. Due to the shorter length it will loose a bit less heat, but not a ton. The main benefit is that I'll be able to insulate the tank to around R40-50. The combination of the two should bring the heat loss down from around 4k btu/day down to 2.4k btu/day. The new shorter design also reduces the maximum stress on the plywood down to a peak of 866 PSI which is about 1/5th the maximum rating of plywood (4500 psi). This should account for any imperfections in the wood, aging of the wood, any effects of thermal cycling, etc which might weaken the tank over time.
