Gardening Tools and Calculators

Free Greenhouse and Gardening Calculation Tools: Share this With You're Friends!

This page contains essential online tools for greenhouse gardening, especially the shopping and research stages of the garden process.

  1. Greenhouse Area Calculator
  2. Greenhouse BTU Calculator
  3. Greenhouse EFM Calculator

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Tool #: 1 - Greenhouse BTUs Heat Calculator Tool

BTU Heating Calculations Explained

The greenhouse BTU calculator was formulated to determine the heating needs of greenhouses, in one easy step!

  • This calculator is designed to calculate and give an estimate of the BTU (British Thermal Unit) greenhouses heat requirements.
  • Simply enter the area to be heated and select the climate adjustments.
  • This is to be used for a general guideline only.

Greenhouse Area 
  • The total square feet of exposed surface area of your greenhouse not including the floor (This is not length * width).
  • To find out the area your greenhouse, click here.

Coldest Outside Temperature 
  • You will want to enter the lowest temperature expected for your area. 
  • Not sure? You can click here for the USDA plant hardiness zones which provide an average annual temperature rating for areas within the United States.

Maximum Inside Temperature 
  • This is the highest temperature you want to maintain in your greenhouse.

Heat Loss Value 
  • Check the table at the bottom of the page to find the heat loss value for the covering used on your greenhouse.
  • Some values may vary with manufacturer.
  • If you know the R-value of your covering, you can convert it to a heat loss value using this formula:
  • Heat loss value = 1 / R-value.

Resulting Minimum BTU 
  • This is the minimum BTU output your heater should have. Most heaters use a BTU input rating.
  • BTU Output = (Heater Efficiency) * (BTU input).
  This result is: Area x (Max - Min) x Heat Loss

Covering Insulation (R) Values for Polycarbonate, Polyethylene, Glass, and Fiberglass
Covering Material R Value Covering Material R Value
3 mm Glass (single layer) 0.95 4 mm Twin-wall Poly 1.43
Two layers of Glass (insulated) 2.00 6 mm Twin-wall Poly
8 mm Twin-wall Poly 1.61 4 mm Polyethylene
10mm Twin-wall Poly 1.89 6 mm Poly 0.87
16 mm Triple-wall Poly 2.50 6 mm Poly double layer (inflated) 1.43
Fiberglass / Poly (single layer) 0.83 11 mm woven Poly 0.95
R value: A unit used to measure the effectiveness of thermal insulation.

Tool #: 2 - Greenhouse Area Calculator

How to Calculate the Area of Greenhouse

The greenhouse area calculator tool is used for researching and calculating the area of a greenhouse structure or conservatory, just enter in the length, width, height, and height of sidewalls!

  • If you have any questions about using this tool or what it's purpose is, contact us and our greenhouse experts will explain how it works and the benefits of using it. 

 Length- in feet
 Width- in feet
 Height - in feet
 Height of Sidewall - in feet
Area of Greenhouse - This number is used to calculate the minimum BTU output needed for your greenhouse.

Tool #: 3 - Greenhouse EFM Calculator

The EFM greenhouse calculator is a tool to determine exhaust fan ventilation output, so you can get the perfect amount of fans and vents in your greenhouse!


Greenhouse Exhaust Fan Ventilation Calculator

 Length of Greenhouse - in feet
 Width of Greenhouse - in feet
 Height of Greenhouse - in feet
Fan CFM Needed - This is the optimal exhaust fan CFM (Cubic Feet per Minute) rating for your greenhouse. A fan this size will exchange the air in your greenhouse one rate per minute which is the recommended ventilation for most small greenhouses.
Choosing Shutters
Exhaust fans require 18 inches (324 sq. in) of air intake area per 1000 CFM to function properly.

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