Rex says
Everyday utility math — the kind you'd otherwise pull up four browser tabs for. I keep it to one clean answer.
Try a scenario
Click to load — tweak from there.Inputs
Result
Peak heat load (BTU/hr)
39,200
Season propane cost
$1,929
Propane needed (gal)
665
Season energy (MMBTU)
51.7
Equivalent kWh
15,165
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One click, a permanent link with your numbers baked in.
How to use this
- 1Enter glazing surface area (sq ft).
- 2Enter u-value of glazing.
- 3Enter target inside temp (°F).
- 4Enter design outside temp (°F).
- 5Enter heating hours per season.
- 6Enter propane price ($/gal).
- 7Read your peak heat load (btu/hr) on the right — it updates as you type.
- 8Hit Share to keep the scenario or send it to someone.
About this calculator
Estimate the heat loss through greenhouse glazing at your design temperature difference, then price the season's fuel for propane, natural gas, or electric heat.
Worked example
Using the values the calculator loads with:
Inputs
- Glazing surface area: 1400 sq ft
- U-value of glazing: 0.7
- Target inside temp: 60 °F
- Design outside temp: 20 °F
- Heating hours per season: 2400
- Propane price: 2.9 $/gal
Results
- Peak heat load (BTU/hr): 39,200
- Season propane cost: $1,929
- Propane needed (gal): 665
- Season energy (MMBTU): 51.7
- Equivalent kWh: 15,165
What each field means
Inputs
- Glazing surface area (sq ft)
- The glazing surface area used in the calculation, measured in sq ft. Starts at 1400 sq ft so you have a working example on load.
- U-value of glazing
- The u-value of glazing used in the calculation. Starts at 0.7 so you have a working example on load. Accepted range: 0.2–1.3.
- Target inside temp (°F)
- The target inside temp used in the calculation, measured in °F. Starts at 60 °F so you have a working example on load.
- Design outside temp (°F)
- The design outside temp used in the calculation, measured in °F. Starts at 20 °F so you have a working example on load.
- Heating hours per season
- The heating hours per season used in the calculation. Starts at 2400 so you have a working example on load.
- Propane price ($/gal)
- The propane price used in the calculation, measured in $/gal. Starts at 2.9 $/gal so you have a working example on load.
Results
- Peak heat load (BTU/hr)
- Returned as a whole number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Season propane cost
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Propane needed (gal)
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Season energy (MMBTU)
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Equivalent kWh
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
Why the 0.55 factor?
Peak load only occurs at the design low. Averaged across a season, actual consumption runs roughly half to 60% of continuous peak.
How much does double poly help?
It roughly halves the U-value versus single layer — usually the cheapest heating upgrade available.
Accuracy and limitations
- Estimates assume standard, average conditions — local rules, pricing, and materials vary.
- Results are rounded for readability; add a buffer before ordering, booking, or committing.
- Double-check anything with a real cost attached against a local quote.
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Greenhouse Heating Cost Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/greenhouse-heating
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/greenhouse-heating" target="_blank" rel="noopener">Greenhouse Heating Cost Calculator — RevenueLab</a> (2026).</p>
Source: [Greenhouse Heating Cost Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/greenhouse-heating) (2026).