A Greenhouse Heating Calculator (GHC) estimates how much heat a Greenhouse or Glasshouse needs to stay at a set temperature during cold conditions. The Greenhouse Heating Calculator works by combining exposed surface area, temperature difference, and a heat loss factor tied to covering type. The main benefits of a Greenhouse heating calculator are accurate BTU output estimates, better heater sizing, and clearer heating cost planning. Common uses include winter protection, seedling propagation, and planning heater upgrades. Core components include a surface area calculator, a heat loss factor table, inside and outside temperature inputs, and a Greenhouse BTU calculator result.

How to Calculate Heat Requirements for Your Greenhouse

To calculate greenhouse heating requirements, multiply exposed surface area by the temperature difference and the heat loss value.
Formula:
BTUs per hour = Exposed surface area × (Inside Temperature − Minimum Outside Temperature) × Heat Loss Value

This calculation provides a baseline heating load for Greenhouses using Imperial (°F, ft²) or Metric (°C, m² converted to ft²) units. The result guides heater size selection and heater efficiency checks.

Step-by-Step Example:

A gable end Greenhouse has 400 sq ft (37.2 m²) of exposed surface area.
The minimum outside temperature is 10°F (−12°C).
The target inside temperature is 60°F (15.5°C).

Temperature difference = 50°F
Heat loss value = 1.10 (single-layer glass)

BTU output needed = 400 × 50 × 1.10 = 22,000 BTUs/hour

Adjustment Factors

Apply reductions to refine the estimate:

• Reduce BTUs by 30% for double glazing or inner liners.
• Reduce BTUs by 30% for a Lean To Greenhouse attached to a heated wall.
• Increase BTUs during high wind shear or exposed sites.

These adjustments improve accurate BTU calculation before equipment upgrades.

Greenhouse Heating Calculator

The Greenhouse Heating Calculator brings surface area calculators, heat loss factor parameters, and temperature inputs into one tool. The calculator supports Electric heaters, propane, natural gas, and paraffin heaters. Results help match heater efficiency to climate conditions and USDA Zone Map ranges.

Greenhouse BTU Calculator

The Greenhouse BTU calculator (GBC) outputs the minimum BTU output a Greenhouse heater must deliver.
If a heater lists BTU input, calculate output as:
BTU output = heater efficiency × BTU input

A heating engineer may use this value for precise energy estimation in larger Greenhouses.

Square surface area calculator for a standard gable end Greenhouse structure

A gable end Greenhouse includes two side walls, two gable ends, and a pitched roof.
Calculate total square feet (or square meters) of all walls and roof surfaces. Do not include the floor. This total exposed surface area feeds directly into the Greenhouse heating calculator.

Square Surface Area Calculator for a Lean To Greenhouse Structure

A Lean To Greenhouse shares one wall with an existing building.
Exclude the shared wall from exposed surface area calculations. This reduction lowers total heat loss and BTU requirements, especially in winter.

Heat loss factor parameters

Heat loss factor depends on Greenhouse covering and insulation. Lower values mean better insulation.

Greenhouse Covering Heat Loss Values (U-value):

• 4 mil polyethylene: 1.20
• 6 mil polyethylene: 1.15
• 4 mm (5/32″) twinwall polycarbonate: 0.70
• 6 mm (1/4″) twinwall polycarbonate: 0.62
• Double layer inflated poly: 0.70
• Single-layer glass: 1.13

R-value = 1 / Heat Loss Value

Twinwall polycarbonate reduces heat loss and heating costs compared to single-layer coverings.

How to use the Greenhouse Heating Calculator

1. Calculate total exposed surface area using the correct structure type.
2. Select the correct heat loss value based on covering and current insulation.
3. Enter the minimum outside temperature and desired inside temperature.
4. Review the Greenhouse BTU calculator result.
5. Match the result to a Greenhouse heater with adequate BTU output and thermostat controls.

How much heat does a Greenhouse need?

A Greenhouse needs enough heat to offset heat loss through its exposed surfaces at the coldest expected outside temperature.
The required heat depends on total square feet, outside temperature, inside temperature, and heat loss factor. The Greenhouse heating calculator converts these values into BTUs per hour.

How much does it cost to heat a Greenhouse?

The cost to heat a Greenhouse depends on BTU requirements, fuel type, heater efficiency, and energy provider rates.
Use the Greenhouse heating calculator result with electricity, propane, or natural gas pricing to estimate heating costs. Costs increase during winter and decrease with better insulation and thermal curtains.

What size Greenhouse heater do I need?

A Greenhouse heater size must meet or exceed the calculated BTU output.
Small Greenhouses may use electric fan heaters. Larger structures often require propane or natural gas systems. Oversizing wastes energy; undersizing risks crop loss.

Which Greenhouse heater is best?

Electric heaters are the safest and most controllable option for most Greenhouses.
Electric fan heaters distribute heat evenly and integrate with thermostat controls. Propane, natural gas, and paraffin heaters suit off-grid locations but require ventilation and monitoring.

What is the most efficient way to heat a Greenhouse?

Electric heaters with good insulation provide the most efficient way to heat a Greenhouse.
Efficiency improves with twinwall polycarbonate, thermal curtains, reduced wind exposure, and automated temperature regulation.