Greenhouse Heating Cost Calculator

Estimate peak heat loss, a practical heater capacity, fuel use, and operating cost for a gable greenhouse or a structure with known envelope measurements.

Calculations run locally in your browser. Use representative night or overcast temperatures; no input is sent or stored.

Greenhouse and Heating Inputs

Changing units converts the values already entered.

Currency changes formatting only; enter your local price.

1. Greenhouse geometry
ft
ft
ft
degrees

Envelope area excludes the floor. For hoop, lean-to, gutter-connected, or irregular houses, use known area and volume.

2. Heat-loss assumptions

Presets are planning values; use the full assembly rating when available.

Btu/h·ft²·°F
ACH
3. Temperature and heating period
°F
°F
hours
days

Cost assumes the entered temperature difference persists during every heated hour. Use a design low for heater sizing or an average cold-period temperature for budgeting.

4. Fuel and heater
/kWh
%
%

Efficiency converts purchased fuel into delivered heat. Price excludes fixed charges, taxes, demand charges, and delivery fees.

Keyboard shortcut: Ctrl/⌘ + Enter to calculate.

Heating Estimate

Enter the greenhouse, weather, and heating assumptions, then calculate.

Advertisement

Formula and Assumptions

The calculator estimates steady-state heat loss during a cold, dark period. It adds transmission through the covering, infiltration from air leakage, and optional foundation-edge loss:

Qtotal = (U × A × ΔT) + (0.02 × V × ACH × ΔT) + (F × P × ΔT)

In U.S. units, heat loss is in Btu/h, U is Btu/(h·ft²·°F), A is above-ground envelope area, V is greenhouse volume, ACH is air changes per hour, F is the perimeter factor, P is ground perimeter, and ΔT is indoor minus outdoor temperature. Metric inputs are converted internally and results are displayed in both kW and the selected unit system.

Purchased fuel = delivered heat ÷ heater efficiency ÷ fuel heat content. Planning heat contents are 3,412.142 Btu/kWh, 100,000 Btu/therm of natural gas, 91,452 Btu/US gal of propane, and 138,500 Btu/US gal of No. 2 heating oil. Supplier values can vary, especially by fuel composition and whether a rating uses higher or lower heating value.

How to Use This Greenhouse Heater Calculator

  1. Choose geometry: enter gable-house dimensions, or switch to known envelope area and volume for a hoop house or irregular structure.
  2. Set covering and leakage: select planning presets, then replace them with manufacturer U-factor and measured or audited ACH when available.
  3. Choose temperatures: use a local winter design temperature for heater sizing or a representative average temperature for cost planning.
  4. Enter operating time: specify heated hours per day and days in the budget period.
  5. Enter fuel details: use the delivered price and a realistic seasonal efficiency, then review load, fuel, and cost.

Worked Example: 20 × 48 ft Double-Poly Greenhouse

A 20 × 48 ft gable greenhouse with 8 ft eaves and a 26.5° roof has about 2,261 ft² of above-ground covering and 10,073 ft³ of volume. At 60°F indoors and 20°F outdoors, U 0.70, 0.75 ACH, and an insulated perimeter edge, the estimate is roughly 71,500 Btu/h (21.0 kW) before a sizing margin.

If electric resistance heat runs 12 hours per day at $0.16/kWh, the steady-temperature estimate is about $40 per heating day. Actual use is normally lower during milder hours and may be higher in wind or where warm air distribution is poor.

Ways to Reduce Greenhouse Heating Cost

Seal air leaks

Repair torn film, weather-strip doors, close fan shutters, and seal gaps at the base. Infiltration can be a large share of the load.

Add a second layer

Inflated double polyethylene can substantially reduce transmission compared with a single film layer.

Use thermal curtains

A properly installed night curtain reduces the effective heat-loss area and creates another insulating air space.

Heat the crop zone

Root-zone or under-bench heat may allow a lower air setpoint for suitable crops, but requires crop-specific management.

Maintain the heater

Combustion tuning, clean heat exchangers, unobstructed flues, and even air circulation help preserve delivered efficiency.

Compare setpoints

Run several indoor temperatures. Heat loss changes directly with the indoor-outdoor temperature difference.

Methodology and Sources

Updated: July 31, 2026. Formulas and planning ranges follow cooperative-extension greenhouse engineering references.

Greenhouse Heating FAQs

How is greenhouse heat loss calculated?

The calculator adds heat transmitted through the above-ground envelope, heat lost through air infiltration, and optional foundation-perimeter loss. Transmission equals U-factor × area × indoor-outdoor temperature difference.

What U-factor should I use for greenhouse glazing?

Use a manufacturer rating for the complete assembly when possible. Typical planning values include about 1.15 Btu/(h·ft²·°F) for single polyethylene film and 0.70 for separated double polyethylene film.

What does ACH mean?

ACH is air changes per hour. New double-film houses are often estimated around 0.5–1.0 ACH; older leaky houses may reach 2–4 ACH. Wind and maintenance affect the real value.

Does the suggested capacity size the heater?

It applies your sizing margin to this calculated steady-state load. Confirm final equipment against local design weather, wind, distribution losses, redundancy needs, fuel supply, ventilation, and manufacturer instructions.

Does this include solar heat gain?

No. It represents night or overcast conditions. Solar gain and heat stored in soil, plants, water, and masonry are excluded.

Why can the actual bill differ?

Weather changes hourly. Solar gain, thermal curtains, equipment cycling, wind, heater condition, ventilation, distribution losses, and tariff structure all affect actual use.

Can I use metric units?

Yes. Metric mode uses metres, square metres, cubic metres, Celsius, and W/(m²·K). Natural gas uses kWh and liquid fuels use litres.

Are my inputs stored?

No. Calculations stay in your browser.

Safety and Planning Limit

This calculator is a budgeting and preliminary sizing aid, not an HVAC, combustion, electrical, structural, or fire-safety design. Greenhouse heaters must be installed with required clearances, ventilation, flues, fuel controls, electrical protection, and carbon-monoxide safeguards. Have final equipment and installation reviewed by qualified local professionals and follow applicable codes and manufacturer instructions.

Explore more tools