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Garage Mini-Split Calculator
A 22 x 22 ft garage with average insulation, normal sun, one person and 1,500 W of tools running needs about 17,800 BTU per hour of cooling, which rounds up to an 18,000 BTU mini-split. Every watt of tool power becomes 3.412 BTU per hour of heat inside the room, so a shop full of motors needs more than an empty garage of the same size.
Mini-split BTUUpdates as you type
17,800 BTU per hour load: shop an 18,000 BTU mini-split
- Envelope and sun
- 12,100 BTU/h (25 BTU/h per sq ft x insulation x sun)
- People
- 600 BTU/h (600 each)
- Tools
- 5,118 BTU/h (3.412 per watt)
- Total cooling load
- 17,818 BTU/h
- Nearest standard size up
- 18,000 BTU/h
The 25 BTU/h per sq ft base, the insulation and sun factors and 600 BTU/h per person are conventions, not code values. A contractor load calculation is the right answer for a big purchase. Check the unit voltage: some DIY units run on 115V, others need a 220-240V circuit.
Mini-splits and moisture control
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Why tools count as a heat source
Every watt of electricity a motor draws ends up as heat in the room, 3.412 BTU per hour per watt. A running dust collector, compressor and welder can add 5,000 to 10,000 BTU an hour to the cooling load, on top of the sun on the roof and the people inside. That is why an empty garage and a working shop of the same size get different mini-splits.
What to check before buying
- Voltage: some DIY 12,000 BTU units run on 115V, others need 208-240V and a disconnect.
- Line set length: a long run to the outdoor unit reduces capacity.
- Heating: a heat pump heats too, but its output falls in deep cold: check the low-temperature rating of the unit you buy.
For the heating side by itself use the heater calculator.
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- Layout and what fits
- Space left with a car
- Workshop amps and subpanel
- 240V circuit sizing
- 240V outlet install cost
- Voltage drop and cords
- Compressor CFM
- Dust collector and duct size
- Garage heater BTU
- Shop lighting
- Air filtration ACH
- Workbench height and depth
- Workbench size for a garage
- Mobile base sizing
- Shop budget planner
Frequently asked questions
What size mini-split for a 2 car garage?
A 22 x 22 ft garage with average insulation and a person working with 1,500 W of tools needs about 17,800 BTU per hour of cooling, which rounds up to an 18,000 BTU unit. A 24,000 BTU unit fits a sunny, uninsulated bay.
Can a mini-split heat a garage too?
Yes, a heat pump mini-split heats and cools, but heating output falls as outdoor temperature drops. Check the manufacturer's low-temperature capacity.
Do I need to size up for the overhead door?
A mini-split cannot keep up with an open door. Size for a closed bay and plan to close the door while it runs.
This page is researched guidance, not professional electrical, engineering or safety advice. Circuits, loads and clearances depend on your house, your service and your town: have a licensed electrician confirm any wiring, and check local code and each manufacturer's manual before you act.
