Is it cheaper to run a mini split or central AC?

Mini split or central AC: the short answer

A mini split is usually cheaper to run than central AC. It has no ductwork to leak cool air, and you only run the heads in the rooms you're using. Central air can match it when the ducts sit inside the heated part of the house, are sealed, and the whole house needs cooling at once.

The U.S. Department of Energy puts duct losses at more than 30% of the energy used for heating and cooling in some homes, mostly where the ducts run through an attic, a crawl space or an unheated garage. A ductless system doesn't have that loss to begin with.

The other half of the saving is habit. Most Duluth homes need cooling for a few weeks in July and August, often only in an upstairs bedroom. Running one 9,000 or 12,000 BTU head there costs far less than starting a whole-house system to cool rooms nobody is in.

When central air costs less

Central air comes out ahead in a few cases:

If your ducts are leaky or run through a cold attic, fixing them is part of the comparison. Sealing and insulating ducts can close much of the gap without changing systems.

How efficiency ratings compare

Cooling efficiency is rated in SEER2: the higher the number, the less power for the same cooling. Ductless heat pumps are commonly rated higher than central air conditioners of the same size. That rating is measured on the equipment, though, not on your house. A high-SEER2 central system feeding leaky ducts can use more power than its label suggests.

Compare the rating, then ask where the cold air goes after it leaves the unit.

What changes in Duluth and Superior

Our cooling season is short. The average July high at the Duluth airport is about 79°, so AC here is about a handful of humid stretches, not months of running. That favors the cheaper-to-install, cheaper-to-run option for the rooms that get hot.