Plan
Greenhouse & cold frame planner
Size your vents, glazing, and thermal mass — then get a forecast-driven open/close schedule so nothing cooks or freezes.
Your structure
Polycarbonate or glass freestanding house, roof + side vents.
Floor area
96 sq ft
Total vent area
19.2 sq ft
20% of floor
Roof / high vents
11.5 sq ft
60% of total, up high
Low side intakes
7.7 sq ft
40% of total, near the ground
If you vent with a fan instead
Air volume is about 538 cu ft, so a summer exhaust fan should move 538 CFM (one full air change per minute). In cool weather, 134 CFM is enough.
Pair any exhaust fan with an intake opening of at least 0.7 sq ft or it will just stall against its own pressure.
Notes for a hobby greenhouse (glazed)
- Roof vents do the work — aim for at least 15–20% of floor area in roof vents.
- Add low side intakes so cool air enters below and exits high (chimney effect).
Automatic vent openers
Match lift capacity to the weight of the vent or lid.
Small wax-cylinder opener
Cold frame lids and small side louvers
up to 15 lb
opens 68–75°F
Standard wax opener
Most hobby greenhouse roof vents
up to 30 lb
opens 68–75°F
Heavy-duty dual-spring opener
Glass roof vents, heavy frames
up to 50 lb
opens 70–80°F
Thermostat + 12V linear actuator
Roll-up sides, big louvers, exhaust shutters
up to 200 lb
opens adjustable