Heat Pump Room Sizing Calculator
Whole-house calculators give you one number for the whole building, but installers need one per room. Add each room with its size and insulation level to get a heating load and recommended unit size for every room. Nothing uploaded.
Results
| Room | BTU/hr | kW | Recommended unit |
|---|---|---|---|
| Total | - | - | - |
Notes
Estimates are based on simple area, insulation, ceiling height, and window-area inputs. Actual heat pump sizing should also account for climate zone, air leakage, and manual J-style load calculations for a final installation decision.
Heat Pump Load Estimation Per Room
How Base Load Changes With Insulation
A room's heating load depends on how fast heat escapes through walls, ceilings, and windows. Well-insulated modern homes lose about 20 BTU per hour per square foot of floor area. Average older homes lose 30, and poorly insulated spaces lose 40. You then add window loss (50 BTU per sqft of glazing) and adjust for taller ceilings.
Standard Unit Sizes and Oversizing
Ductless mini-splits come in fixed sizes: 9,000, 12,000, 18,000, 24,000 BTU/hr and up. This calculator picks the smallest standard size that covers your calculated load. Slight oversizing (moving up one step) is acceptable and helps with dehumidification, but undersizing causes the unit to run constantly and wastes energy.
FAQ
What is a reasonable estimate for heating load per room?
Base load depends heavily on insulation. A well-insulated room needs about 20 BTU/sqft, average insulation needs 30, and poorly insulated rooms need 40. You also add extra load for windows and adjust for ceiling height. This calculator combines all factors to give a custom load per room.
Why do you need to size each room separately?
Ductless mini-splits put one compact indoor unit in each room or zone. The outdoor compressor can handle multiple zones, but each zone needs its own capacity. A large living room might need 24,000 BTU/hr while a small bedroom only needs 12,000, so you can't use one size for the whole house.
How do I know if a 12,000 or 18,000 unit is right?
This calculator recommends the smallest standard unit size that covers the room's calculated load. Oversizing slightly (one step up) is okay and gives better dehumidification, but undersizing causes the unit to run continuously and waste energy. The calculator's recommendation is the safe minimum.