Greenhouse Heating Calculator

Calculate BTU heating requirements for a greenhouse based on glazing, dimensions, and temperature differential.

Inputs

Length

Width

Sidewall Height

Glazing Type

Inside Temperature

°F

Outside Design Temp

°F

Wind Exposure Factor

Tab to move between fields

Results

Heating Load

201,692 BTU/hr

Daily Heat Requirement4,840,609 BTU/day

Total Surface Area5,457 sq ft

Floor Area2,880 sq ft

Natural Gas48.41 therms/day

Propane52.9 gal/day

Electric Heat1,418.7 kWh/day

How to Use This Calculator

Enter your greenhouse dimensions (length, width, sidewall height in feet) and select the glazing type — double poly has the best insulation for the cost.
Enter your desired inside temperature (°F) and the coldest expected outside design temperature for your location.
Set the wind exposure factor: 1.0 for a sheltered site, 1.2 for moderate exposure, 1.5 for open/exposed locations.
Review the Heating Load (BTU/hr) — this is the peak output your heater must provide on the coldest night.
Compare Natural Gas (therms/day), Propane (gal/day), and Electric Heat (kWh/day) to choose the most economical fuel source.

How the result changes with Inside Temperature

Inside Temperature	Heating Load
45	128,349 BTU/hr
58	176,022 BTU/hr
73	231,029 BTU/hr
85	275,035 BTU/hr

What each input means

Length: Greenhouse length in feet.
Width: Greenhouse width in feet.
Sidewall Height: Height at the eave/sidewall.
Glazing Type: Covering material affects heat loss rate (U-value).
Inside Temperature: Desired greenhouse temperature.
Outside Design Temp: Coldest expected outside temperature for sizing.
Wind Exposure Factor: 1.0 for sheltered, 1.2 for moderate, 1.5 for exposed sites.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Length = 96, Width = 30, Sidewall Height = 10, Glazing Type = 3 = 7 input(s) provided
Calculate Heating Load
Heating Load
201692 = 201692
Calculate Daily Heat Requirement
Daily Heat Requirement
4840609 = 4840609
Calculate Total Surface Area
Total Surface Area
5457 = 5457

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