Best Greenhouse Heater for Winter

The best greenhouse heater for winter depends on greenhouse size, insulation, climate, power access, and what temperature you actually need to maintain. For a small home greenhouse, an electric heater with a fan and thermostat is usually the simplest option. For larger structures, heat loss calculations and safety become more important.

The goal is not always to make a greenhouse warm like a house. Many gardeners only need frost protection or a cool minimum temperature for seedlings and overwintered plants.

For structure costs, read Greenhouse Kit Cost: Small vs Large.

Last updated: June 6, 2026.

Quick Answer

For most small home greenhouses, choose a greenhouse-rated electric fan heater with a thermostat, tip-over protection, splash-resistant design, and enough capacity for the space. Place the thermostat near plant height. Use propane or gas heaters only with proper ventilation, manufacturer guidance, and carbon monoxide safety.

Electric vs Propane Greenhouse Heaters

For most hobby gardeners, electric heat is easiest because it avoids combustion gases. The greenhouse still needs airflow and moisture control.

How Warm Should a Greenhouse Be?

Match temperature to the crop:

Do not heat an entire greenhouse to tomato-growing temperatures if you are only overwintering hardy potted plants. The electricity or fuel cost can be much higher than expected.

Thermostat Placement

Place the thermostat:

• near plant height
• away from direct heater blast
• out of direct sun
• not touching the greenhouse wall
• near the coldest plant area if frost is the concern

A thermostat mounted near the ceiling can read warmer than the plants. A thermostat near the heater can shut off too soon.

Insulation Helps More Than Oversizing

Before buying a larger heater, reduce heat loss:

• seal obvious gaps
• use weather stripping where appropriate
• add bubble insulation designed for greenhouses
• use thermal curtains at night
• place tender plants together
• raise pots off cold floors
• use water barrels as thermal mass if space allows

Heating an unsealed greenhouse can waste money quickly.

Safety Checklist

Use this checklist before running heat:

• outdoor-rated or greenhouse-rated electrical connections
• no overloaded extension cords
• heater kept away from plastic, fabric, and leaves
• stable surface
• drip protection
• GFCI-protected circuit where appropriate
• working thermostat
• backup thermometer
• carbon monoxide detector if combustion heat is used
• ventilation for propane or gas heaters

Combustion heaters can add moisture as well as heat, which can make condensation and disease worse.

Operating Cost

Electric heat is easy to estimate:

heater watts / 1000 x hours running x electricity rate = cost

A 1,500-watt heater that runs for 6 hours uses 9 kWh. At $0.18 per kWh, that is about $1.62 for that night. Cold snaps can be much more expensive because the heater cycles longer.

FAQ

Can I use a regular space heater in a greenhouse?

Only if it is suitable for the environment and used safely. Greenhouses are damp, crowded, and often have plastic materials nearby. A greenhouse-rated unit is a safer choice.

Is propane cheaper than electric heat?

It depends on local fuel and electricity prices, greenhouse size, and ventilation losses. Propane can produce strong heat, but safety requirements are higher.

Do I need a fan with a greenhouse heater?

Usually yes. Moving air helps distribute heat and reduce cold pockets. It also helps manage humidity.

Related Reading

• How Much Electricity Do Grow Lights Use?
• Greenhouse Ventilation Mistakes
• How to Prevent Mold in a Greenhouse
• Polycarbonate vs Glass Greenhouse

Sources

• Cornell: Greenhouses for Homeowners
• UF/IFAS: Greenhouse Ventilation
• EIA: Short-Term Energy Outlook, Electricity
• University of Minnesota Extension: Starting Seeds Indoors