Tune airflow for healthy plants without bill shock. Enter fan specs, runtime, and your rate. Get daily, monthly, and yearly costs in seconds now.
Use this sample to sanity-check your inputs and expected output shape.
| Scenario | Fans | Running watts | Hours/day | Months | Rate | Estimated annual cost |
|---|---|---|---|---|---|---|
| Circulation, thermostat cycling | 2 | 120 W | 10 | 8 | $0.20/kWh | ~ $46.85 |
| Exhaust, daily summer use | 1 | 300 W | 12 | 4 | $0.22/kWh | ~ $115.63 |
| Nursery, year-round circulation | 4 | 85 W | 16 | 12 | $0.18/kWh | ~ $357.70 |
1) Convert fan power to watts
2) Compute daily energy (kWh) per fan
3) Apply schedule and seasonal adjustments
4) Energy and cost
Fan labels often list a maximum draw, while real consumption depends on static pressure, speed setting, and motor condition. Use measured watts when possible, or estimate from voltage, amps, and power factor. Small errors in watts become meaningful over long runtimes, especially in multi-fan houses. A 20 W difference on four fans running 12 hours daily adds about 350 kWh per year before seasonal scaling.
Greenhouse fans rarely run at a constant duty cycle. Thermostats, humidistats, and variable-speed controls create cycling that can cut energy use without sacrificing plant health. The season intensity input models cycling by scaling annual usage, while active months reflect the true growing-season window. If you operate only on workdays, select a weekly schedule instead of assuming daily operation.
Many bills include tiered rates, taxes, or time-of-use pricing. Enter a blended rate for a quick estimate, or run separate scenarios for day and night schedules. If demand charges apply, energy cost is not the whole story, but kWh remains the baseline for comparing fans, controls, and setpoints. For audits, align the rate period with your billing cycle to reduce material reporting errors.
Oversized fans, restrictive louvers, dirty shutters, and blocked inlets raise pressure and increase electrical draw. Cleaning, belt alignment, and maintaining bearings can reduce watts and improve airflow. Consider high-efficiency motors or EC fans where applicable, and verify that airflow targets are met with the lowest practical power. Sealing obvious leaks can reduce run time by reaching temperature and humidity targets faster. Recheck watts after each maintenance quickly.
Export results to CSV or PDF and keep a log for each zone, including crop stage, weather band, and control setpoints. A monthly comparison can reveal drifting power consumption, control faults, or opportunities for schedule refinement. Use this calculator as a repeatable method to justify upgrades with transparent assumptions and documented savings.
Q1: Should I use watts or volts and amps?
Use watts if you have a reliable measured value. If you only have volts and amps, include a realistic power factor to avoid overestimating motor energy.
Q2: What is a good power factor if I do not know it?
Many small motor loads are around 0.85 to 0.95. Using 0.90 is a practical default for planning, then refine with a meter reading later.
Q3: How do I model thermostat cycling?
Keep active hours realistic, then reduce season intensity to reflect cycling, such as 60 to 80 percent. This captures partial-load behavior without needing minute-by-minute data.
Q4: Why include standby watts?
Timers, controllers, and smart relays can draw power even when the fan is off. Over a year, small standby loads can add up, especially across many circuits.
Q5: Can this estimate multiple fan types?
Yes. Run one calculation per fan type or zone, export each result, and combine the annual kWh and cost in a spreadsheet for whole-facility totals.
Q6: What if my rate changes seasonally?
Run separate scenarios using your seasonal rates and months, then add the costs. This provides a clearer budget than using one average rate for the entire year.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.