Mini Split Sizing Calculator

Estimate a one-zone cooling load, compare nominal mini split sizes and check your own design cooling and heating loads.

Quick estimate

Plan a mini split for one zone

Start with a room or zone area. The area rate is an illustrative planning assumption; a proper design load and equipment match require Manual J and Manual S.

Project and measurements

Results update automatically as inputs change.

Calculation result

One-zone cooling load
—

View key breakdown

Detailed results and planning tools

View calculations, report and comparisons

Calculation breakdown

These values reflect the editable inputs and assumptions above.

QuantityValue

Calculation report

Includes formulas, entered assumptions, limitations and sources.

Enter valid inputs to create a report.

Compare scenarios

Keep up to three alternatives to compare measured values and assumptions.

Quick answer#

Estimate a one-zone cooling load, compare nominal mini split sizes and check your own design cooling and heating loads. The result updates as you edit inputs. Choose a contextual example to populate visible fields, then replace the example with your actual measurements or professional design values.

Formula and calculation method#

The illustrative load is conditioned zone area × the editable load rate. A supplied cooling design load replaces that illustration. Nominal catalog sizes are a comparison, not a product recommendation.

US customary and metric inputs use one internal SI calculation path. Each displayed quantity is converted after the calculation. Presets only fill editable inputs; no undocumented material, performance or cost adjustment is made.

Worked example#

A 300 ft² zone at an illustrative 20 BTU/h per ft² yields 6,000 BTU/h. Enter an actual design load when available; check manufacturer capacity at the design conditions.

Open the calculator above, select the matching example and review every dimension or rate before using the result. The PDF report includes your entered values and documented limits.

Selecting inputs and project assumptions#

The input units change together when you switch measurement systems. A project preset is a starting point, not an instruction to buy a product or select a construction assembly. Local materials, engineering plans and supplier quotations have priority over illustrative defaults.

Cost inputs, if available, use only the numbers you provide. The currency selector changes the label and does not fetch exchange rates or regional prices. The calculation report identifies its formula, input assumptions and sources.

Assumptions and limitations#

An area factor does not account for climate, insulation, windows, leakage, internal gains, humidity or equipment modulation. This is not a Manual J load calculation or Manual S selection, and a nominal size is not delivered capacity.

Use this result for preliminary planning. Measure the actual project, obtain the required design or specification, confirm available product sizes and tolerances, and verify purchases with the supplier or contractor. A calculation cannot inspect site conditions or guarantee a finished quantity.

Sources and methodology#

  • ACCA Manual J — reference for the relevant method, standards or units; no source certifies these illustrative presets.
  • ACCA Manual S — reference for the relevant method, standards or units; no source certifies these illustrative presets.
  • U.S. DOE on HVAC sizing — reference for the relevant method, standards or units; no source certifies these illustrative presets.

Sources support the stated method and context. Any editable preset or illustrated cost is an Efficienco example, not a quotation, standard-prescribed value or endorsement by the linked organization.

Frequently asked questions

Does square footage alone size a mini split?No. The area estimate is only an editable planning example. Use a room-by-room Manual J design load and Manual S equipment selection before purchasing.
What does the cooling design load override do?It replaces the area-based planning figure in the displayed load and nominal-size comparison.
Can I enter a heating load?Yes. If you also enter the unit’s delivered heating capacity at design outdoor temperature, the tool shows a capacity gap.
Are the 15, 20 and 25 rates official sizing rules?No. They are clearly labeled illustrations for exploring sensitivity, not ACCA or DOE load factors.
Does nominal BTU/h equal real output?No. Delivered capacity depends on the unit and design conditions; compare manufacturer performance data.
Can one zone represent an entire home?No. Multiple rooms and zones may require separate loads, distribution planning and equipment selection.