Wine cellar BTU calculator

How this calculation works

Heat enters a cellar four ways, and the total of all four is what the cooling unit has to remove every hour:

• Conduction through walls, ceiling and floor — surface area × U-value × temperature difference. Doubling insulation roughly halves this term, which is why the insulation question matters more than the brand of unit.
• Glass — a thin, poorly insulating surface, plus direct solar gain that can dwarf everything else on a west-facing window.
• Internal loads — people at about 400 BTU/h each, and lights. LED strips are close to negligible; a bank of incandescent spots is not.
• Door openings — air exchange each time someone walks in. Modelled here as a flat 10%.

We then add a 15% safety margin, because real rooms have thermal bridges, gaps and imperfect assumptions. Finally we derate for ambient: a unit rated at 90°F loses roughly a tenth of its rated capacity for each 10°F above that, so a 105°F garage needs meaningfully more nameplate capacity than the same room in a cool basement.

What this model does not do

It assumes steady state. When you first load 300 bottles at 70°F into a 55°F cellar, the cooling unit faces a large one-time pull-down load — allow 24-48 hours, and don't panic-size the unit for it. It also assumes no active moisture control: humidity management is a separate question, covered in temperature and humidity.

For anything above about 2 tons (24,000 BTU/h), or any build using refrigerant lines, get a refrigeration engineer to sign off on the design. The arithmetic here tells you what to ask them, not what to skip.