Determine the size of the storage tank for the purposes of exposed square footage. This is crucial for the determination of heat flow out of the tank. For instance, if the storage tank is 12 feet high and has a diameter of 8 feet, then the circumference is PI (3.1416) x diameter and the surface area is the circumference multiplied by the height. This is calculated by 3.1416 x 8 x 12 or 302 square feet.

Determine the heat transfer rate through the tank metal. This can be located on a table such as one found in the references. For instance, if the tank is insulated, exposed and has a liquid inside at a temperature of 90 degrees Fahrenheit, then the heat transfer rate (α) is 0.4 Btu/hr ft^2 F.

Determine the ambient (atmospheric) temperature the storage tank will be exposed to. For instance, assume it is winter and the temperature drops to 30 degrees F.

Calculate the heat loss from the storage tank using the formula Q = α x A x dt, where Q is the heat loss in Btu/hr, α is the heat transfer rate in Btu/hr ft^2 F, A is the surface area in square feet and dt is the temperature difference of the tank fluid and ambient temperature. This is calculated to be 0.4 x 302 x (90-30) or 7,248 Btu/hr of heat loss.