Glossary · Energy, bills & ratings
Full-load hours (equivalent full-load hours)
Also called: EFLH
The number of hours a heating or cooling system would have to run flat out to deliver a whole season's heating or cooling.
What it means
Real equipment cycles on and off and often runs below full output, so energy calculators turn a season's demand into an equivalent number of hours at full capacity. NRCan's air conditioner cost formula does this with cooling degree-days: 24 × cooling degree-days ÷ (summer design temperature − 18°C). Multiply the full-load hours by the unit's capacity and divide by its efficiency to estimate the energy it uses.
Why it matters in an audit
It's how a calculator turns your local climate into a yearly kWh estimate for an air conditioner or heat pump: the more full-load hours, the more a high-efficiency unit saves.
Typical numbers
Reference values with their sources. Your energy advisor’s report gives the figure for your own house.
| What | Value | Source |
|---|---|---|
| NRCan cooling formula (base 18°C) | Full-load hours = 24 × cooling degree-days ÷ (summer outdoor design temperature − 18) | natural-resources.canada.ca ↗ |
| Worked example | 200 cooling degree-days and a 30°C design temperature: 24 × 200 ÷ 12 = 400 full-load hours | Arithmetic |