How Much Heat for a Small 10×8 Greenhouse at 0°F Outside?
Calculate how many BTUs are needed to keep a small 10×8 hobby greenhouse at 45°F on a 0°F night.
How to use this tool
- Enter the greenhouse interior dimensions in feet.
- Enter your target minimum inside temperature and the coldest expected outside temperature.
- Select the glazing type (material covering the greenhouse).
- The result shows surface area, temperature difference, and required heater BTU/hr output.
Small hobby greenhouses still need properly sized heaters for cold climates — calculate your BTU requirement here.
Frequently asked questions
- How do I calculate greenhouse heating requirements?
- Multiply the greenhouse surface area × temperature difference (inside minus outside) × the glazing U-value. This gives BTU/hr required. Always add 20–25% as a safety margin.
- What temperature should I maintain in a greenhouse?
- For frost protection only, maintain 34–40°F. For cool-season crops (lettuce, kale), 45–55°F. For tomatoes and peppers, 60–70°F nights. Higher targets need significantly more heating.