Mini-split for a garage

A 12-24k class mini-split heat pump runs about $3,000–$7,000 installed, against about $750–$1,700 for a plain 240V resistance heater sized to the same garage. In a sealed 2-car garage in Chicago, the heat pump's lower running cost usually closes that gap inside 5 years — and unlike the resistance heater, it also cools.

The real seasonal COP, not the nameplate number

A mini-split's rated output is set at a 47°F outdoor temperature — not a Chicago January night. As the outdoor temperature drops, both its capacity and its coefficient of performance (COP, heat delivered per unit of electricity) fall. At this garage's 3.3 °FSFrom a manual or spec sheetEXAMPLE_A_STATION.h99 (ASHRAE 99% design dry-bulb)Report a problem design temperature, a standard-class unit rated for 24,000 BTU/hSFrom a manual or spec sheethp_12_24k_230 top of class, 47degF AHRI ratingReport a problem can only deliver about 13,900 BTU/hCComputed by our engineheatPumpCapacity('standard', h99, 24000) — lib/planner/seasonal.tsReport a problem at a COP of about 1.7CComputed by our engineheatPumpCop('standard', h99)Report a problem. A cold-climate/hyper-heat model holds up better — about 18,700 BTU/hCComputed by our engineheatPumpCapacity('cold_climate', h99, 24000)Report a problem at the same outdoor temperature.

Bin-integrated over a whole heating season in this sealed garage (qDesign about 18,400 BTU/hCComputed by our engineplan() on ceilingIns:R30, tightness:tightReport a problem, grade B), a standard-class unit averages a season-wide COP of about 2.5CComputed by our engineheatPumpSeasonal('standard', ...) — lib/planner/seasonal.tsReport a problem; cold-climate averages about 2.7CComputed by our engineheatPumpSeasonal('cold_climate', ...)Report a problem. Both numbers already include the resistance backup that kicks in whenever the compressor can't keep up — that's normal, not a malfunction.

On the coldest nights, a standard-class unit still only covers about 76 %CComputed by our enginecapAtDesign / sealed qSizeReport a problem of this sealed garage's design load; cold-climate gets to about 102 %CComputed by our enginecapAtDesignCold / sealed qSizeReport a problem. Either way, check the manufacturer's low-ambient capacity curve against your own design temperature before assuming the nameplate BTU number is what you'll actually get in January.

5-year cost: heat pump vs. a plain resistance heater

Same sealed garage, same seasonal load, two ways to cover it — a 12-24k mini-split heat pump, or a right-sized 7.5 kW electric resistance heater:

Savings vary. Find out why in the seller's fact sheet on R-values. Higher R-values mean greater insulating power.

At the midpoint of each install range, the heat pump comes out several hundred dollars ahead over 5 years of running cost alone — before counting cooling. But installed price is the real swing factor: at the cheap end for resistance and the expensive end for the heat pump, resistance wins outright. Get an actual installer quote before treating either total as settled.

Also runs backward: cooling

The same outdoor/indoor unit reverses in summer to cool the garage — useful if it doubles as a shop, gym or hangout space in July. BayHeat's cooling load calculator isn't live yet, so this page doesn't quote a cooling BTU/h or a summer running cost; treat the cooling capability as a real feature of the equipment, not a number to plan around until that calculator ships.

Why not sealing skips this

• Why not a DIY pre-charged mini-split, 12k class (115V)? A DIY pre-charged 115V mini-split tops out around 12,000 BTU/h on a shared 120V/20A circuit — enough for a small, already-sealed 1-car bay, not this comparison's 2-car load, and it skips the licensed refrigerant charge check most manufacturers require for warranty.

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Safety: GO · PER MANUAL

Next step

Run your own garage through the planner → to see whether it's sealed enough for a mini-split to actually cover the coldest night, or whether fixing the envelope first gets you there for a lot less money.