The BTU/h value shown here is a theoretical number. There are often circumstances under which a cellar design may require a larger unit due to variables not accounted for in the formula. For example, these variables could be building materials (such as glass, stone, concrete, etc.) which do not offer the insulation capacity required to maintain the optimal cellar environment. We recommend purchasing a unit with a larger capacity to compensate for these unaccounted-for variables. An undersized unit can lead to premature failure and will most likely prevent the cellar from reaching your desired temperature.