Tools you might need next
Calculate optimal seed spacing, plants per row, and rows per bed for vegetable garden planning and efficient seed placement.
Convert NPK fertilizer ratios and calculate precise application rates per square foot for lawns, gardens, and raised beds.
Calculate cubic feet and cubic yards of soil mix needed to fill your raised garden beds from length, width, and fill depth.
Loss depends on surface area, U-value of glazing, and temperature difference between inside and outside.
BTU/hr ≈ U × area × ΔTAir leaks and frequent door openings add load. Vented poly houses lose more heat than double-wall polycarbonate.
Add 10% to 25% margin so the heater can recover after a cold snap or windy night.
Updated: July 2026
Compare heat load at 45°F inside when outside drops to 15°F in USDA zone 5.
See how better glazing cuts BTU needs and heater cost over a season.
Model lower night temperatures to right-size heaters for frost protection only.
Design for the lowest expected night temperature plus wind, not the monthly average.
Open fields and ridge-top sites increase infiltration loss. Add margin or use windbreaks.
Size a heater before cold nights arrive. Enter greenhouse dimensions, insulation, and temperature targets to estimate heat loss and required BTU output.