Some tanks on the market lack insulation on the bottom. If you want to get an idea how this affects heat loss just observe what happens to a puddle of water at the bottom of such a tank. It boils!
Our tanks have a fully insulated the bottom as well as the tops and sides to minimize heat loss and reduce fuel usage. We use 3 inches of insulation on the bottom and 6 inches on the sides and top.
We then install a metal plate over the entire bottom to cover the insulation and protect it from damage.
Several years ago we created a spreadsheet to compare the heat losses for our TAV30 tank with the heat losses of a similar Gencor tank. The Gencor tank has a much greater heat loss because it has no insulation on its bottom and only 4 inches on its sides and top.
So heat loss for the Gencor tank is 129 million Btu/year greater than ours.
Consequently, it takes almost 1,000 more gallons of No. 2 fuel to heat the Gencor tank every year than it takes to heat our tank. Think of what that adds up to over a period of 20 years. The difference is stunning!