What size mini-split do I need for a 24x30 insulated garage in Moncton NB?

For a well-insulated 24x30 garage in Moncton, you're looking at a mini-split in the 18,000 to 24,000 BTU (1.5 to 2 ton) range, though the right size depends on several factors specific to your build and how you plan to use the space.

Why Sizing Matters More Than You'd Think

A 24x30 garage is 720 square feet — larger than many NB apartments. The naive approach is to multiply square footage by a rule-of-thumb BTU factor, but that method was designed for conditioned living space, not a garage in a climate that swings from -25°C in February to +30°C in August. Undersizing means the unit struggles on the coldest days and never reaches your target temperature. Oversizing means the unit short-cycles, doesn't dehumidify properly, and costs more upfront than necessary.

Moncton sits in the 4,800-5,000 heating degree day range, which is a serious heating load. Your mini-split needs to handle sustained cold snaps, not just average winter temperatures. This is where cold-climate mini-splits become essential — standard mini-splits lose efficiency and capacity rapidly below -10°C, while cold-climate models (Mitsubishi Hyper Heat, Daikin Fit, Bosch, LG Artcool) maintain meaningful heating output down to -25°C or colder. In Moncton, a standard mini-split is not sufficient as a primary heat source — you need a cold-climate rated unit.

The Key Variables That Affect Your Sizing

Insulation quality is the biggest factor. A properly insulated 24x30 garage in NB means R-20 walls (2x6 framing with batt insulation), R-40 to R-50 ceiling, and an insulated concrete slab or at minimum a well-sealed floor. If your garage has R-12 walls and minimal ceiling insulation, your heat loss is dramatically higher and you'll need more BTUs. If you're using closed-cell spray foam on the walls and ceiling, you could potentially get away with the lower end of the range.

Garage door insulation matters enormously. Two garage doors on a 24x30 represent a significant percentage of your total wall area. Uninsulated steel doors (R-2 to R-4) are essentially holes in your building envelope. Insulated doors rated R-16 or higher make a measurable difference in your heating and cooling load — and they're worth the upgrade if you're going to the trouble of conditioning the space.

Intended use affects your target temperature. If you want 15°C for basic vehicle protection and occasional use, your load is lower than if you want a comfortable 20°C workshop where you spend hours at a time. Size for your actual use case.

Ceiling height is often overlooked. A standard 10-foot garage ceiling gives you 7,200 cubic feet of volume to condition. If you have a 12-foot ceiling or a bonus room above with an open stairwell, your volume increases substantially.

Practical Sizing Guidance

For a well-insulated 24x30 garage in Moncton with standard 10-foot ceilings, insulated doors, and R-20 walls:

A 24,000 BTU (2-ton) cold-climate mini-split is the most common recommendation and gives you comfortable headroom for the coldest Moncton days. If your insulation is exceptional (spray foam, R-30+ walls, R-50 ceiling, R-16+ doors), an 18,000 BTU unit may be sufficient and will cost less to purchase and operate.

For electrical, a 24,000 BTU mini-split typically requires a dedicated 240V, 20-30 amp circuit. This needs to be planned with your electrician and permitted — don't assume your existing garage panel has capacity.

NB-Specific Considerations

Mini-splits in NB garages handle both heating and cooling, which is genuinely useful — Moncton summers get humid and warm, and a garage workshop in July without cooling is uncomfortable. The dehumidification function in cooling mode also helps manage the moisture that snow-covered vehicles dump into your garage in winter.

Have a licensed HVAC contractor perform a proper Manual J heat load calculation before purchasing. The calculation accounts for your specific insulation values, window area, door area, air leakage, and local design temperatures. It takes about an hour and removes the guesswork entirely. Installing the wrong size unit is an expensive mistake in a $1,500-$4,000 piece of equipment.

You can find HVAC contractors through the New Brunswick Construction Network at newbrunswickconstructionnetwork.com — and if you need help finding a garage builder to handle the full insulated garage build, New Brunswick Garages can match you with local contractors for free.