Mini split sizing Last reviewed June 30, 2026
What Size Mini Split for a Basement? BTU Guide
By the WhatSize editorial team 5 min read Standards-reviewed
Most basements up to 800 sq ft need 12,000 BTU. Large finished basements (800-1,200 sq ft) need 18,000-24,000 BTU. Basements need 15% less capacity than above-ground rooms due to stable ground temperatures.
Why Basements Need Less Capacity
Basements have a natural advantage: the surrounding earth maintains a stable temperature (50-60°F year-round in most climates). This means the mini split doesn't have to work as hard to cool the space. The ACCA Manual J standard applies a 0.85 multiplier for basement spaces.
A 1,000 sq ft basement in a central climate would need about 17,000 BTU (1,000 × 20 × 0.85), which means a 12,000-18,000 BTU mini split. This is 15-30% less than an above-ground room of the same size.
However, don't undersize for basements that aren't fully finished. Unfinished basements with exposed concrete, poor air sealing, and no insulation in the rim joist areas may actually need standard or oversized equipment.
Top picks for this size
These Amazon-available picks meet the calculated spec. For region-specific or licensed contractor-installed options, consult a local professional. See our Disclaimers.
Basement Mini Split Sizing Guide
- 400-600 sq ft basement: 12,000 BTU
- 600-900 sq ft basement: 12,000-18,000 BTU
- 900-1,200 sq ft basement: 18,000-24,000 BTU
- Unfinished basement: Use standard sizing (ignore the 0.85 discount) — open concrete and gaps leak conditioned air
Frequently asked questions
What size mini split do I need for a basement?
Yes. Mini split indoor units are only 9-12 inches deep and mount high on the wall. For basements with 7-foot ceilings, install the unit within 6 inches of the ceiling. Ceiling cassette units are also available for very low headroom.
Should I get a heat pump mini split for my basement?
Basements need heating more than cooling. A heat pump mini split provides both, and the heating is especially valuable in basements that are naturally cool. The Pioneer heat pump series works down to -13°F outdoor temperature.
How do drainage and condensate work in a basement mini split?
Unlike an upstairs unit that can rely on gravity drainage, a basement mini split needs a condensate pump to push water up and out. Many modern units have built-in pumps. If yours doesn't, you'll need an external condensate pump ($80-120).
You might also need
More mini split sizing guides
- What Size Mini Split for a Garage? Complete BTU Guide
- What Size Mini Split for 1,000 Sq Ft? BTU Calculator
- 9,000 BTU vs 12,000 BTU Mini Split: Which Size Do You Need?
- Mini Split Sizing for Florida: Complete BTU Guide
- What Size Mini Split Do I Need for a Bedroom?
- How Many BTU per Square Foot? (Mini Split Sizing Chart)
- Mini Split Sizing for Hot Climates (AZ, TX, FL, NV)
- How Many Mini Splits Per Outdoor Unit? Multi-Zone Sizing Guide
- What Size Mini Split for a Living Room? BTU Guide
Still choosing between sizes? Compare: 9,000 vs 12,000 BTU