Sizing a ductless mini-split head per zone

Ductless systems are sized zone by zone: each head serves one room directly, so there is no duct loss and no shared load — compute a load per zone, then pick the nominal rung at or above it.

Three room boxes on the left — Living at 11,000, Bedroom at 5,200, and Bonus room at 8,400 BTU per hour of zone load — each with an arrow to a matched indoor head of 12k, 6k, and 9k. On the right, a ladder of nominal capacity rungs from 6,000 up to 36,000 BTU per hour, with the picked rungs highlighted as the first one at or above each zone load. — Source: ACCA Manual J per-zone loads; manufacturer nominal capacities

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Three room boxes on the left — Living at 11,000, Bedroom at 5,200, and Bonus room at 8,400 BTU per hour of zone load — each with an arrow to a matched indoor head of 12k, 6k, and 9k. On the right, a ladder of nominal capacity rungs from 6,000 up to 36,000 BTU per hour, with the picked rungs highlighted as the first one at or above each zone load.

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