Adding heat to a greenhouse opens up year-round growing for warm-season crops, but it also adds cost, complexity, and maintenance. An unheated greenhouse is simpler and cheaper to run, but limits what you can grow in winter. Here’s how to decide what’s right for your situation.
| Factor | Heated Greenhouse | Unheated Greenhouse |
|---|---|---|
| Winter crops | Full range: tomatoes, peppers, herbs, tropicals | Cold-hardy only: greens, root veg, overwintering |
| Season extension | Year-round growing (all 12 months) | 3–4 season growing (spring–late fall) |
| Seed starting | Start seeds as early as January | Start seeds March–April (weather dependent) |
| Operating cost | Moderate to high (energy costs) | Minimal (no energy costs for heating) |
| Setup complexity | Heater + thermostat + monitoring | Simple: structure + ventilation only |
| Risk of crop loss | Lower (controlled environment) | Higher in extreme cold snaps |
| Equipment needed | Heater, thermostat, backup power plan | Thermal mass, row covers, cold frames |
| Ideal for | Year-round producers, tropical growers, market farms | Season extenders, hobby growers, budget-conscious |
If you want to grow tomatoes in January, start seeds in midwinter, keep tropical plants alive through northern winters, or produce for a market year-round, you need heat. The investment pays for itself through extended production seasons, earlier harvests, and higher-value crops. A well-insulated twin-wall polycarbonate greenhouse with a thermostat-controlled electric heater can maintain 50–60°F through most winters in moderate climates at reasonable cost.
Heating costs scale with insulation quality, greenhouse size, climate severity, and target temperature. A well-insulated 8×12 greenhouse in USDA Zone 6–7, maintaining 50°F overnight with a 1,500W electric heater, typically adds a moderate amount to your monthly electric bill during the coldest months. Poorly insulated or oversized structures cost proportionally more.
An unheated greenhouse still provides enormous value. It extends your growing season by 2–4 months on each end, protects from frost, wind, and hail, and creates a sheltered environment for hardening off transplants. Cold-hardy crops like lettuce, spinach, kale, mache, and claytonia actually grow better in the cool, protected greenhouse environment than outdoors.
Going unheated eliminates energy costs, simplifies maintenance, removes fire risk from heaters, and reduces the overall investment. Thermal mass (water barrels, stone floors) and row covers inside the greenhouse provide enough frost protection for cold-hardy crops in most climates.
Many experienced growers use a zone-heating strategy: the greenhouse itself stays unheated, but seedling heat mats provide bottom warmth for seed starting, and a small heater protects a partitioned section during the coldest nights. This captures most of the benefit of heating at a fraction of the cost.
Another hybrid: heat the greenhouse actively only during the seed-starting season (January–April), then let it run unheated through the mild months. This approach provides year-round utility without year-round heating bills.
Start unheated and add heat as your needs (and budget) dictate. An unheated greenhouse provides tremendous value on its own. Most growers who eventually add heating wish they’d insulated better before buying the heater—so invest in insulation first. See our guides on heating efficiency and insulation.