Standard uninsulated garage doors leak air and radiate heat. Block walls may have no insulation. Calculators assume poor insulation unless you have upgraded the shell.
A 400 sq ft two-car garage workshop may calculate 12,000–18,000 BTU with poor insulation — 18,000 BTU is common before you insulate. After insulating doors and walls, recalculate — you may drop to 12,000 BTU.
Workshop heat gains beyond sq ft
Size for peak use when machines run and doors stay closed — not empty garage volume alone.
Welding, compressors, and dust collection motors add heat
South-facing garage doors act like radiators in afternoon sun
Epoxy curing and paint booths need ventilation — exhaust air replaces cooled air
Occasional use vs daily use: modulating inverter helps part-time shops
Install and electrical notes
Mount indoor head away from dust-heavy zones — filters clog faster in workshops. Mount outdoor condenser where lawn equipment will not hit it.
Many 12k–18k BTU units need 220V. Run dedicated circuit before closing drywall if finishing the garage. Permit and code rules apply — this is planning info, not electrical advice.
Frequently asked questions
What size mini-split for a 24×24 garage?
576 sq ft uninsulated calculates high — often 18,000 BTU or more. Insulate the door and walls first, then expect 12,000–18,000 BTU. Enter dimensions with poor insulation selected.
Should I insulate the garage door before installing AC?
Strongly yes — panel kits and bottom seals cut load dramatically. Cooling an uninsulated metal door garage is expensive and never comfortable.
Is a mini-split safe in a dusty woodworking shop?
Keep filters maintained and consider air filtration in the shop zone. Mini-splits do not bring in fresh air — ventilation is separate from cooling load planning.
HVAC Calculators provides estimates for planning only — not professional HVAC engineering or installation advice. Verify sizing with a licensed contractor before purchasing equipment. Read disclaimer