Heat load by glazing type, floor area, and temp delta — plus propane gallons per month.
Heat load
ΔT = 35°F
8,750 BTU/hr
Recommended heater size
1.25× heat load for headroom
10,938 BTU/hr
Wall surface
floor × 2.5 (gambrel approximation)
500 sq ft
Propane (continuous)
1 gal propane = 91,000 BTU
69 gal / month
This sizes worst-case peak heat load at the coldest outdoor temp you design for. Real fuel burn is less — the heater cycles off whenever temps rise above design minimums. Use the monthly propane figure as a ceiling, not an average.
Every layer of plastic roughly halves heat loss. Twin-wall polycarbonate pays back in fuel savings in one or two seasons in cold climates.
BTU/hr = U × wall_sqft × (indoor − outdoor)
wall_sqft = floor_sqft × 2.5
propane_gal/month = (BTU/hr × 720) ÷ 91,000
Seed Starting Calendar
Work back from your last frost date to the right day to sow indoors, transplant, and direct-seed.
Planting Density
How many plants fit a row or bed? Enter spacing and area; get plant count and seed order quantity.
Irrigation Needs
Gallons per plant per day by crop, climate, and system efficiency — with weekly water cost.