Plant engineering calculator · Updated 17 September 2026
Boiler Standby & Cycling Loss Calculator — Idle Energy, Cycling & Annual Cost
Screen both idle standby loss and repeated start/stop cycling in one canonical boiler-loss workflow. Keep measured/OEM loss data explicit instead of hiding it behind generic assumptions.
Inputs
Live results
- Standby loss 75.00 kW
- Annual standby energy 225000 kWh
- Annual cycling energy 66000 kWh
- Combined avoidable energy 291000 kWh
- Annual standby cost 180000
- Annual cycling cost 52800
- Combined annual cost 232800
Formula and method
Standby kW = rated fuel input × standby-loss fraction. Standby energy = standby kW × idle hours. Cycling energy = cycles/day × extra fuel/cycle × operating days. Combined cost = (standby + cycling energy) × fuel-energy price.
Worked example
A 5 MW fuel-input boiler at 1.5% standby loss exposes 75 kW while idle. Adding 8 cycles/day at 25 kWh extra fuel per cycle for 330 days reveals the separate cycling penalty instead of burying it inside standby loss.
When this is useful
Use it when comparing current controls with wider turndown, lead/lag staging, thermal storage, or a smaller summer boiler. Run measured scenarios before and after control changes.
Assumptions and limits
- Use measured/OEM standby loss where available; standby percentage is not a universal boiler constant.
- Extra fuel per cycle should come from trend data, burner/OEM data or a defensible site estimate. Purge, warm-up, shell and distribution losses vary by plant.
Frequently asked questions
Is cycling loss the same as standby loss?
No. Standby loss occurs while equipment is idle/hot; cycling loss is the incremental fuel associated with repeated shutdown, purge, warm-up and restart events.
Should I create a separate boiler cycling calculator?
No. These intents overlap heavily, so this page keeps one canonical owner and compares both loss mechanisms without creating a duplicate URL.