How-to Guide
How to Heat and Ventilate a Greenhouse in Winter
The short answer
Heating and ventilation work together in a winter greenhouse. Heat keeps the crop above its minimum temperature; a hobby greenhouse in a cold-winter climate generally needs auxiliary (supplemental) heat because passive sun alone won't hold temperatures on the coldest nights. Ventilation and air circulation keep that heat evenly distributed so you don't get warm and cold pockets that stress plants.
For circulation while heating, run small fans sized so their airflow capacity is about one quarter of the greenhouse's air volume — enough to keep temperatures uniform without dumping heat. Design choices help too: insulating the north wall keeps daytime heat from escaping at night, and passive-solar 'deep winter' designs capture and store solar heat to cut the heating load.
Heating
- In cold-winter climates a hobby greenhouse generally needs auxiliary heat — passive solar alone won't hold minimum temperatures on the coldest days.
- Insulate the north wall to keep daytime-generated heat from escaping and to buffer against cold night temperatures.
- Passive-solar 'deep winter' greenhouse designs store solar heat (in soil/rock thermal mass) to reduce heating needs.
Ventilation and air circulation
- While heating in winter, keep air circulating so temperatures stay uniform throughout the greenhouse.
- Small circulation fans with an air-moving capacity equal to about one-quarter of the greenhouse's air volume are sufficient.
- Heating and ventilation systems are both vital to holding proper temperatures for crops.
→ Match your target minimum temperature to the crops you're overwintering, then size heating and circulation to hold it evenly.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- Clemson HGIC — Hobby Greenhouses — Keep air circulating while heating so temperatures stay uniform; small fans sized to ~one-quarter of greenhouse air volume; heating and ventilation both vital.
- University of Minnesota Extension — Deep winter greenhouses — Passive-solar deep-winter design captures and stores solar heat in thermal mass; insulated north wall retains daytime heat overnight.
- Oregon State University Extension — Does a greenhouse need auxiliary heat in winter? — Cold-climate greenhouses generally need supplemental (auxiliary) heat in winter to hold crop temperatures.