How to Heat a Greenhouse in Winter

On this page (9 sections)

1. How to heat a greenhouse without wasting warmth
2. How much heat does your greenhouse need?
3. Which heater suits your greenhouse setup?
4. How should you set up the heater and thermostat?
5. What temperature should you set?
6. How can you reduce heater running costs?
7. How do you manage moisture while heating?
8. Which mistakes cause cold spots or unsafe heating?
9. How should you choose your greenhouse heating setup?

To work out how to heat a greenhouse, first reduce heat loss, then choose a heater that can maintain your plants' minimum temperature. Measure conditions at plant height rather than judging warmth beside the heater.

Frost protection and growing tender plants through winter are different goals. A lower temperature target needs less heat, so decide what your plants require before choosing equipment.

How to heat a greenhouse without wasting warmth

Seal unwanted drafts and shrink the heated area before adding more heating capacity. Loose panels, door gaps, and unused space all increase the work a heater must do.

Repair the structure first, then consider a suitable inner insulating layer. Keep insulation clear of heaters and follow the greenhouse maker's guidance about attachments and panel loads.

Group plants with similar needs together. An inner growing area can reduce the volume you need to warm, provided it leaves space for airflow and safe heater clearances.

For realistic cold-weather expectations, read whether greenhouses work in winter. If you're still choosing the structure, compare greenhouses suited to winter use.

How much heat does your greenhouse need?

Heat loss and the temperature gap matter more than floor area alone. Holding a greenhouse just above freezing takes less energy than keeping the same structure warm enough for tender plants.

Greenhouse height, cover material, wind exposure, and air leaks affect demand. A heater's coverage estimate cannot account for every combination, so don't choose equipment from square footage alone.

All 4 heaters below have a maximum output of 1500W. Switching between them changes controls and placement options, but doesn't give you a higher maximum electrical heating input.

If you're planning a new structure, our greenhouse size guide helps you avoid heating space you won't use. For frame and cover choices, start with backyard greenhouse types.

Which heater suits your greenhouse setup?

Choose by temperature control, moisture exposure, and placement needs once you've checked heating capacity. These models suit different setups, even though their maximum wattage is the same.

Choosing controls for heating a greenhouse

A separate thermostat helps control temperature where plants grow, rather than relying only on conditions beside the heater. Position its sensor according to the instructions and use a separate thermometer to check the result.

The VEVOR with thermostat suits growers who want an independent controller and a compact floor-mounted heater. Its steel body, carry handle, and heating and fan modes suit a sheltered growing area where you can keep the unit dry.

Skip it for splash-prone placement: its IP20 rating provides no water protection. It includes overheat protection, but you still need clear intake and outlet space rather than squeezing it between pots.

The TRUSTECH suits growers who want a digital target, 750W and 1500W heat choices, and fan-only operation. Its adjustable tilt helps direct airflow along a clear aisle rather than into nearby foliage.

Skip it if you need a thermostat setting below 40°F. The waterproof sensor probe doesn't make the heater waterproof, and its 7.5 ft cord still needs to reach a suitable outlet without an extension.

The ZIZIWIN suits growers who want a heater and digital thermostat together, with adjustable temperature and ventilation settings. At 3.5 lb, it's also a practical option if you need to reposition it between suitable growing areas.

Skip it if your buying decision depends on a specific thermostat range that you haven't confirmed. Automatic cycling can shorten runtime once the target is reached, but it won't solve excessive heat loss.

The second VEVOR suits growers who want a floor-mounted heater with fan operation and a 25° adjustable angle. Its IPX4 splash protection is a useful distinction where incidental moisture is a concern.

Skip it if you want an included independent thermostat for automatic temperature control. Splash protection doesn't permit irrigation spray or dripping condensation, and any added controller must be suitable for the heater and used as its instructions allow.

For a wider equipment comparison, see our greenhouse heaters guide. Browse the greenhouse heating and cooling category for related accessories.

How should you set up the heater and thermostat?

Prepare a dry, stable position and a suitable electrical supply before switching the heater on. Follow the model's required mounting surface and clearances rather than placing it wherever there's an empty gap.

Keep the heater clear of plastic walls, covers, leaves, stored supplies, and watering routes. Direct warm air through open space rather than onto seedlings or one group of pots.

Plug it directly into a suitable wall outlet with appropriate ground-fault protection. Don't use an extension cord or power strip, and keep the cord away from wet floors, door edges, and foot traffic.

Check the circuit's capacity alongside other connected equipment. If the supply is unsuitable or uncertain, have a qualified electrician assess it before use.

Place an air-temperature sensor near plant height, away from direct sun, cold walls, and the heater's discharge, as its instructions allow. If a controller uses a soil probe, follow its intended use rather than assuming its reading represents the surrounding air.

What temperature should you set?

Use the minimum temperature your plants need, with enough margin to account for colder spots and thermostat cycling. There is no single winter setting that suits every greenhouse.

Cold-tolerant dormant plants may need much less warmth than actively growing tender plants. Check the needs of each crop, then separate groups if their requirements differ widely.

Use a minimum-maximum thermometer near the most vulnerable plants. Check another point farther from the heater to find cold pockets that a single thermostat sensor might miss.

Watch overnight lows as the weather changes. If the heater runs continuously while temperatures fall, improve insulation, reduce the heated area, or move sensitive plants somewhere warmer.

How can you reduce heater running costs?

Lower heat loss and avoid heating beyond your plants' needs. A thermostat saves runtime by switching the heater off when the target is reached, rather than changing how much heat the structure loses.

At full output, a 1500W heater uses 1.5 kWh per hour. Multiply that by its actual running hours and your electricity rate to estimate energy use.

A lower power setting can suit mild conditions, but it may run longer. Don't assume half the wattage means half the energy needed to hold the same temperature.

Water containers can store some daytime warmth, but they need sunlight and space. For insulation and passive measures, read how to keep a greenhouse warm.

How do you manage moisture while heating?

Combine gentle air movement with ventilation when needed to manage condensation. Heating air and moving it around don't remove water from the greenhouse.

Open vents during suitable conditions when moisture builds up, then adjust them before temperatures drop. Avoid leaving a door open through a cold night simply to deal with condensation.

Water early enough for spills and wet surfaces to dry when practical. Check soil before watering, since cool winter conditions can change how quickly pots dry.

Fan-only mode supports circulation but cannot cool below the incoming air temperature. Our guide to greenhouse vents, fans, and doors explains how air exchange fits into the setup.

Which mistakes cause cold spots or unsafe heating?

Blocked airflow, misplaced sensors, and ignored overnight lows can undermine an otherwise suitable setup. Check these before buying another heater.

• Putting the sensor in warm airflow: the heater may shut off while distant plants remain cold.
• Packing pots against cold walls: move sensitive plants inward and leave room for air to circulate.
• Covering plants beside the heater: keep fabric and plastic outside all required clearances.
• Trusting daytime warmth: sunshine can hide how sharply temperatures fall after sunset.
• Treating overheat shutoff as permission for unattended use: follow the heater's operating limits.
• Ignoring dirt and debris: switch off, unplug, and let the unit cool before cleaning accessible grilles as directed.

If space is tight, using a mini greenhouse can help you plan plant groups and access. For structural weather risks, read greenhouse safety basics for wind, snow, and heat.

How should you choose your greenhouse heating setup?

Choose TRUSTECH for two heat levels and a defined digital temperature range, or ZIZIWIN for a thermostat kit with adjustable ventilation. Choose the first VEVOR for its independent thermostat in a dry setup.

The second VEVOR fits growers who value adjustable airflow direction and splash protection, and can confirm a suitable control arrangement. For any model, successful greenhouse heating depends on matching heat demand and checking plant-level temperatures.

If you're deciding how to heat a greenhouse through severe cold, settle the insulation and backup plant location before relying on a small heater. Polycarbonate greenhouse panels are one part of the structure to assess.

Start with how to keep a greenhouse warm if heat escapes quickly. Once the enclosure is ready, compare greenhouse heating and cooling accessories for the controls and equipment your setup needs.

Frequently asked questions

What is the best way to heat a greenhouse in winter?

Reduce heat loss, then use a suitable thermostat-controlled heater to maintain the temperature your plants need; seal drafts, insulate where practical, and measure the overnight minimum at plant height. If the heater runs continuously without reaching the target, reduce the heated area or reassess the heating capacity.

Can I use a space heater in a greenhouse?

Use a space heater only if its instructions permit your greenhouse conditions and you can meet its clearance and electrical requirements. Keep it away from irrigation and dripping condensation, use appropriate ground-fault protection, and plug it directly into a suitable wall outlet rather than an extension cord or power strip.

Should a greenhouse heater run all night?

Run a greenhouse heater overnight only when its instructions permit that use and the installation meets its safety requirements. A thermostat cycles the heat as needed, but it doesn't guarantee safe unattended operation; check overnight minimum temperatures and have a warmer place ready for vulnerable plants if heating fails.

How do I keep a greenhouse warm without electricity?

Seal drafts, add suitable insulation, and shelter plants within a smaller covered area to slow heat loss; water containers can store some daytime warmth and release it after sunset. These measures depend on available sunlight and weather, so move sensitive plants somewhere warmer when frost protection cannot be maintained.