Mini Split Sizing Calculator

Inputs

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Conditioned room or zone area served by the indoor head.
ft²
Average room height. Load is normalized to an 8 ft room and scaled by volume.
in
Rough cooling BTU/h per square foot at a 20 F indoor-outdoor design temperature difference before modifiers.
Btu/h*ft2 @20F
Rough heating BTU/h per square foot at a 70 F indoor-outdoor design temperature difference before modifiers.
Btu/h*ft2 @70F
Outdoor summer design temperature minus indoor cooling setpoint.
°F
Indoor heating setpoint minus outdoor winter design temperature.
°F
Cooling modifier for solar exposure and glass area.
Envelope modifier for insulation, air leakage, windows and room adjacency.
Adds a small cooling allowance for occupants beyond the first person.
Computers, appliances or process load in the room. Added to cooling load only.
W
Capacity margin applied after the larger of cooling or heating load.
%
Approximate supply airflow used for the CFM sanity check. Actual ductless indoor-head airflow comes from manufacturer data.
cfm/ton

Results

Default result
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Design cooling load (q_c)
9,862 Btu/h
Pass

area load with average sun, average envelope, occupant and equipment gains

Also computed

Design heating load (q_h) Pass 12,250 Btu/h

area heat-loss screen with average envelope

Required capacity with margin (q_req) 13,470 Btu/h

larger of cooling and heating load after sizing margin

Suggested nominal size (q_nom) Pass 15,000 Btu/h

next common ductless nominal size at or above the screened requirement

Nominal cooling tons (TR) 1.25 ton

nominal BTU/h divided by 12,000

Airflow screen (Q_air) 437.5 cfm

nominal tons times the entered CFM/ton screen

Nominal utilization (U) Pass 89.8 %

screened load fits inside the suggested nominal size

Method notes 3 notes
  • This is a first-pass room or zone screen, not a certified Manual J load calculation or Manual S equipment selection.
  • Formula basis: area x load factor x height factor x design delta-T ratio x envelope modifiers, plus cooling-only internal gains.
  • Final ductless selection must check latent load, window data, infiltration, room-by-room diversity, indoor-head throw/noise, manufacturer low-temperature heating capacity, connected-capacity limits, line length, charge and local code.

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