The process in five steps
- Baseline: room volume × 300 BTU/h per m³.
- Adjustments: multiply by city, sun, insulation and window factors, plus top-floor and heat-source factors if ticked.
- Occupants: add 600 BTU/h for each person beyond the first two.
- Uncertainty: turn the point estimate into a range whose width depends on how typical the room is.
- Verdict: compare the model’s rated capacity with the range and report PASS, BORDERLINE or FAIL.
1. Cooling-load baseline
We start from an empirical formula published in TVTC training material: length × width × height × 300 BTU/h, with dimensions in metres. It is an approximate starting point used in Saudi technical training, not a building-design standard and not a substitute for an HVAC load calculation.
2. Adjustment factors
These multipliers are our own estimation model, not government values. They are deliberately modest: their job is to stop the estimate relying on floor area alone, not to simulate software such as HAP or EnergyPlus.
| Input | Option | Factor |
|---|---|---|
| City / climate | Riyadh · Jeddah | × 1.03 |
| Dammam / Khobar · Madinah | × 1.04 | |
| Makkah | × 1.05 | |
| Taif | × 0.97 | |
| Abha | × 0.93 | |
| Other city | × 1.00 (and a wider range) | |
| Sun exposure | Mostly shaded · Average · Strong direct sun | × 0.95 · × 1.00 · × 1.08 |
| Insulation | Good · Average · Poor · Unknown | × 0.92 · × 1.00 · × 1.12 · × 1.06 |
| Windows and glazing | Few / small · Average · Large / many | × 0.97 · × 1.00 · × 1.08 |
| Roof exposed / top floor | Ticked | × 1.08 |
| Kitchen or heat-generating equipment | Ticked | × 1.12 |
| Occupants | Each person beyond two | + 600 BTU/h |
3. Uncertainty range
| Situation | Range | Estimate quality |
|---|---|---|
| Typical room, city and insulation known | ± 10% | Good |
| City is “Other” or insulation is unknown | ± 13% | Medium |
| Area above 60 m², ceiling above 3.4 m, or heat-generating equipment | ± 16% | Medium |
| Area above 100 m² or ceiling above 4.2 m | ± 20% | Low |
“Quality” describes confidence in the estimate, not a certificate that any particular unit is correctly engineered. Inputs are validated: room dimensions, occupants and capacities outside realistic bounds are rejected with field-specific messages rather than silently clamped.
4. Verdict bands
| Rated capacity of the model | Verdict |
|---|---|
| Below 92% of the lower edge | FAIL · clearly undersized |
| 92%–100% of the lower edge | BORDERLINE · near the lower edge |
| Within the range | PASS · preliminary fit |
| Up to 18% above the upper edge | BORDERLINE · slightly oversized |
| More than 18% above the upper edge | FAIL · clearly oversized |
| Estimated load above 60,000 BTU/h | BORDERLINE · professional calculation needed |
The oversized vs undersized guide explains what each side of the range means in practice.
5. A complete worked example
A 4 × 5 m room with a 2.8 m ceiling in Riyadh, strong direct sun, poor insulation, large windows, a top-floor roof and three regular occupants:
| Step | Calculation | Result (BTU/h) |
|---|---|---|
| Baseline | 4 × 5 × 2.8 × 300 | 16,800 |
| Riyadh | × 1.03 | 17,304 |
| Strong sun | × 1.08 | 18,688 |
| Poor insulation | × 1.12 | 20,931 |
| Large windows | × 1.08 | 22,605 |
| Top floor | × 1.08 | 24,414 |
| Third occupant | + 600 | 25,014 |
| Range (± 10%) | 22,512–27,515 |
An 18,000 BTU/h unit is below 20,711 BTU/h (92% of the lower edge), so it fails as clearly undersized; a 24,000 BTU/h unit is a PASS. The same room with average sun, insulation and windows on a lower floor needs about 17,300 BTU/h, which is why the checker asks for conditions instead of only floor area.
Open this example in the checker
The link fills every value except the top-floor box; tick “Roof exposed to direct sun / top floor” to reproduce the table exactly.
6. Model-specification ratios
If you enter Input Power, we show ratios derived only from the capacity and power you supplied: EER = BTU/h ÷ W, and COP = (BTU/h × 0.29307) ÷ W. They help you read the specification; we do not turn them into a bill or claim an official efficiency grade. Annual energy use, if entered, is displayed exactly as copied from the model’s energy label. The spec converter uses the same arithmetic and adds plausibility checks.
7. Dehumidifier planner method
The dehumidifier planner anchors capacity to ENERGY STAR’s published bands by moisture condition and space size. For effective areas above 700 sq ft (floor area × ceiling height ÷ 8), it may raise only the lower end of the band in 5-pint steps. Running cost uses watts × compressor-on hours, or measured kWh per day if you have a smart-plug reading.
8. What we do not calculate
- Measured air leakage or actual wall and glazing U-values.
- Detailed latent humidity load, air distribution or duct design.
- Compressor performance at every outdoor temperature.
- Electricity tariffs, household bills or multi-year ownership cost—those belong to Saudi Home Energy.
Change log
- October 19, 2026: published every factor, uncertainty rule and verdict band on this page; added the spec converter and new guides on the energy label, T1/T3 ratings and fit.
Sources checked for this page
- TVTC — plumbing and electrical installations training material — empirical room-volume formula used as the baseline.
- ENERGY STAR — Dehumidifiers key efficiency criteria — efficiency context for the dehumidifier planner.
Checked on October 19, 2026. Standards change: verify current requirements in the official SASO records before relying on a threshold.