Calculate Greenhouse Heating Demand
Enter your greenhouse dimensions, temperatures, covering type, airflow assumptions, and safety margin to estimate hourly heating demand.
Formula Used
Temperature difference: ΔT = Inside temperature − Outdoor temperature
Conduction loss: Conduction BTU/hr = Surface area × U-value × ΔT
Air infiltration loss: Infiltration BTU/hr = 0.018 × Greenhouse volume × Air changes per hour × ΔT
Ground loss: Ground BTU/hr = Floor area × Ground loss factor × ΔT
Gross heat load: (Conduction + Infiltration + Ground) × Climate exposure multiplier
Net design load: (Gross heat load − Solar credit) × (1 + Safety factor)
Required heater input: Design load ÷ Heater efficiency
This layout estimates steady-state heating demand. Actual needs can vary with crop density, thermal curtains, internal mass, bench layout, and transient weather swings.
How to Use This Calculator
- Enter the greenhouse length, width, sidewall height, and roof rise in feet.
- Set your target inside temperature and the winter outdoor design temperature.
- Choose the glazing or cover type that best matches the structure.
- Estimate hourly air changes based on leaks, vents, and door activity.
- Add optional ground loss, solar credit, safety factor, and heater efficiency.
- Click Calculate Heating Load to show results above the form.
- Review the heat loss breakdown and heater size guidance.
- Use the CSV and PDF buttons to save your result summary.
Example Data Table
| Length (ft) | Width (ft) | Sidewall Height (ft) | Roof Rise (ft) | Inside Temp (°F) | Outside Temp (°F) | Cover Type | ACH |
|---|---|---|---|---|---|---|---|
| 30 | 18 | 8 | 4 | 60 | 20 | Double Poly Film | 1.5 |
| 48 | 24 | 10 | 5 | 65 | 10 | 8mm Polycarbonate | 1.2 |
| 72 | 30 | 12 | 6 | 55 | 5 | Single Glass | 2.0 |
Heating Load Graph
The graph shows how required heater input changes as outdoor temperature shifts. Calculate once to populate the chart.
FAQs
1. What does this calculator estimate?
It estimates greenhouse heating demand in BTU per hour using structure size, covering performance, temperature difference, infiltration, and extra design margin.
2. Why does glazing type matter so much?
Glazing changes the U-value, which controls conductive heat loss. Better-insulated coverings reduce BTU needs and can significantly shrink heater size.
3. What is a good air change assumption?
Tighter houses may operate near 1.0 ACH, while drafty structures can exceed 2.0 ACH. Use a conservative value when uncertain.
4. Should I include a safety factor?
Yes. A safety factor helps cover wind spikes, imperfect sealing, heater cycling, and unusual cold events. Many growers use 10% to 20%.
5. Does this replace a professional heating design?
No. It is a planning calculator for quick sizing and comparison. Commercial projects may need detailed engineering and equipment selection.
6. Why is heater input higher than design heat load?
The heater must deliver enough usable heat after efficiency losses. Lower combustion or transfer efficiency increases the required input rating.
7. Can I subtract daytime solar gain?
Yes. The solar heat credit field lets you reduce the net load. Keep winter nighttime scenarios separate because solar gains disappear.
8. Which units does this calculator use?
Dimensions use feet, temperature uses degrees Fahrenheit, and heating demand is reported in BTU per hour, kilowatts, and tons equivalent.