Two different types of power
Cooling capacity describes how much heat a unit can remove. Electrical input describes the electricity it uses. A unit with 3.5 kW of cooling capacity does not therefore automatically draw 3.5 kW of electricity.
| BTU/h | Approximate kW |
|---|---|
| 7,000 | 2.05 |
| 9,000 | 2.64 |
| 10,000 | 2.93 |
| 12,000 | 3.52 |
| 14,000 | 4.10 |
Convert the units
1 kW of cooling is approximately 3,412 BTU/h. A 12,000 BTU/h rating therefore means roughly 3.52 kW of cooling capacity. Product names often shorten this to “BTU”; our calculations use the rate, BTU/h.
Floor area is only the starting point
Ceiling height, sun exposure, insulation, glazing and indoor heat sources all affect the load. Our calculator uses an educational assumption of 30–50 W per cubic metre, followed by a sunlight factor. It is not a sizing standard or a professional heat-load assessment.
Compare like with like
Check the test method and conditions in the technical documents. A nominal rating does not represent every loss in a real installation, including those around the window and exhaust duct. Extra rated capacity does not reliably fix poor exhaust routing.
Keep the data-sheet quantities separate
Record cooling capacity in kW or BTU/h separately from electrical input in W or kW. The first helps explore heat load; the second feeds the kWh calculation. Their ratio depends on operating point and test method. A single nominal figure should not become a promise of annual running costs.
Worked example: a 75 m³ room
A 30 m² room with a 2.5 m ceiling contains 75 m³. At the intermediate model assumption of 40 W/m³, the result is 3,000 W: 3 kW or 10,236 BTU/h. A sunlight factor of 1.2 raises that to 3.6 kW, approximately 12,283 BTU/h. This represents a changed assumption, not a measurement of your home.
Understand the sensitivity range
The displayed ±20% varies the result around your input assumptions. It is not a probability of success and was not calibrated against a sample of homes. Hose losses, infiltration, building thermal mass and people are not modelled individually. A low starting estimate therefore does not prove that a unit will be adequate during intense heat.
When to seek a fuller assessment
Attics, mezzanines, extensive glazing or commercial use can exceed the scope of a quick estimate. Collect a floor plan, orientation, occupancy schedule and heat-source information before speaking to a specialist. Do not simply add separate bedrooms together: airflow paths and doors may be the main constraint.
Turn the guidance into a room plan · 1
Enter volume and sunlight, then compare a cautious estimate with cooling capacity. This helps with shortlisting but does not guarantee a particular indoor temperature.
Turn the guidance into a room plan · 2
Calculation example, not a product measurement: 20 m² × 2.5 m × 40 W/m³ gives 2 kW. The check’s 20% allowance takes it to 2.4 kW. Sunlight, insulation and ceiling height change this result.
Turn the guidance into a room plan · 3
Do not transfer that figure to the electricity calculator. Cooling at 3.5 kW does not mean drawing 3.5 kW of electricity. You need the exact variant’s electrical input.
Sources and methodology
These sources explain the technical context. They do not validate FREATH ONE or our calculator assumptions.
U.S. Department of Energy — Portable Air ConditionersOFEN / BFE — Étiquette-énergie / Energieetikette