Do You Need a Thermostat for a Greenhouse Heater?

You need a thermostat for automatic on-and-off control around a chosen temperature. Without one, you’ll need to manage the heater yourself, and the temperature can shift while you’re away.

Check the heater manual first. If its built-in thermostat suits your plants and growing conditions, an extra controller may not be necessary.

If the heater lacks temperature control, use an external controller that’s compatible with its electrical load.

A thermostat controls when equipment runs, but it can’t make an undersized heater warm a cold, drafty greenhouse. Sun, wind, gaps, and the distance between the probe and plants also affect temperatures around the space.

For help deciding whether your setup needs heat, see heated vs unheated greenhouses. If you’re still choosing a heater, compare options in our guide to greenhouse heaters with a thermostat.

How does an external greenhouse thermostat work?

An external thermostat measures temperature at a probe and controls power to connected equipment. In heating mode, it switches the heater according to the set point and control settings.

A plug-in controller sits between the outlet and a compatible heater. The probe measures temperature inside the greenhouse, so its placement affects when the heater turns on and off.

Controllers differ in their temperature ranges, supported modes, controls, and electrical limits. Some support heating only; others have separate heating and cooling functions.

What should you check before connecting a greenhouse thermostat?

Check that the controller supports heating and can handle the heater’s electrical load. Compare the heater’s requirements with the controller’s voltage, current, and wattage limits, and follow both manuals.

A higher wattage limit does not guarantee that a controller suits every heater. Confirm that the plug, outlet, and intended use are appropriate for your setup; ask a qualified electrician if you’re unsure.

The Inkbird ITC308 has a temperature probe, Fahrenheit and Celsius display, and calibration. Choose it if you want both heating and refrigeration connections; skip it if you only need a basic heating-only controller.

The DEWENWILS controller supports heating and cooling modes, temperature calibration, and power memory. Its display is designed to remain visible in dim spaces, but verify that its controls and load rating match your setup before choosing it.

Where should you place the greenhouse thermostat probe?

Place the probe near the plants whose temperature matters most, roughly at their growing height. Keep it out of direct sunlight and away from the heater’s hot air, doors, vents, and cold greenhouse walls.

Sunlight can warm the probe faster than the surrounding air, while a sensor beside a heater may shut off heating before plants elsewhere reach the same temperature. Secure the probe so it won’t fall or rest against a surface that reads differently from the air.

Follow the controller’s instructions for probe placement. A separate thermometer can help you compare readings around the growing area.

Our guide to greenhouse thermometers explains how to check conditions.

What temperature should you set on a greenhouse thermostat?

Set the thermostat according to the plants you’re growing and the coldest conditions you need to manage. There isn’t one ideal temperature for every greenhouse or crop.

Check plant-specific temperature needs, including nighttime conditions. A greenhouse may warm during the day and cool quickly after sunset, so an afternoon reading alone may miss the overnight low.

After setting the controller, compare its reading with a thermometer near plant level. Adjust the probe position if it sits in a warm pocket of air or a colder corner that doesn’t reflect the growing area.

For more help with temperature ranges and daily conditions, read what temperature a greenhouse should be.

Can one greenhouse thermostat control a heater and a fan?

Only a controller designed for both heating and cooling can control equipment in both modes. Some plug-in thermostats have separate heating and cooling connections, while others are intended for heating devices alone.

Don’t assume that two outlets perform different jobs. Check the controller’s instructions to confirm what each outlet does, what load it supports, and whether your intended combination is allowed.

A fan helps move hot air out of the greenhouse, but its placement and airflow also matter. See our guide to greenhouse exhaust fans for help choosing ventilation.

The VIVOSUN controller has a dual LED display, a probe, and separate heating and cooling modes. Choose it if you need both functions and its stated 1500W output fits your equipment; skip it if a simpler heating-only controller is enough.

Which greenhouse thermostat suits your heater?

Choose according to your heater’s load, the temperature range you need, and whether you need heating only or cooling too. The controller with the most features isn’t automatically the right match.

The BN-LINK is designed for heating devices, including greenhouse heaters, seedling heat mats, and heat lamps. Its range is 40–108°F and its maximum load is 1000W, so choose it when those limits fit your setup; skip it if you need cooling control or a lower set point.

For a controller with both heating and cooling functions, compare the Inkbird, DEWENWILS, and VIVOSUN based on the features and limits you need. Check the heater manual and controller instructions before connecting equipment.

What mistakes should you avoid with a greenhouse thermostat?

Avoid mismatching the controller and heater, placing the probe in a misleading spot, or assuming a thermostat can solve poor insulation. Each can leave plants colder or warmer than intended.

Don’t connect a heater before confirming the controller’s mode and electrical limits. A heating-only controller can’t manage cooling equipment, and a controller’s outlet capacity must suit the heater.

Don’t put the probe in direct sun, beside a heater, or against a cold wall. Check temperatures near plants and in more than one spot, especially after moving the probe or changing the heater settings.

A thermostat won’t compensate for heat loss through gaps or a damaged cover. If a torn cover is contributing to the problem, see how to replace a walk-in greenhouse cover.

How do you choose the right greenhouse thermostat setup?

Use a built-in heater thermostat if it meets your needs; otherwise, match an external controller to the heater and place its probe near the plants. The right choice depends on the controls and temperature range you need, as well as the heater’s electrical requirements.

Choose the BN-LINK for compatible heating-only equipment that fits its range and load. Consider the Inkbird if you want its heating and refrigeration connections, the DEWENWILS if its controls and output fit your heater, or the VIVOSUN if you need its separate heating and cooling modes.

After setup, compare the controller reading with a thermometer near plant level and check it during cold weather. For help deciding whether to add heat to your growing plan, read heated vs unheated greenhouses.

Frequently asked questions

Does a greenhouse heater need a thermostat?

A greenhouse heater needs a thermostat if you want it to switch on and off automatically around a chosen temperature. Some heaters have built-in controls; others need a separate controller.

Check the heater manual and the controller's heating mode, electrical limits, and sensor placement before connecting them.

Where should I put a greenhouse thermostat probe?

Place the probe near the plants you want to protect, at a height that reflects their growing area. Keep it out of direct sunlight, away from the heater's hot air, vents, doors, and cold walls.

Follow the controller instructions and use a separate thermometer to compare readings.

Can I use any plug-in thermostat with a greenhouse heater?

No. The controller must support heating and be rated for the heater's electrical load.

Some controllers are for heating devices only, while others also support cooling.

Check the heater's manual and the controller's voltage, current, and wattage limits before use.

Is a thermostat the same as a greenhouse thermometer?

No. A thermometer shows the temperature, while a thermostat can control a connected heater around a set point.

A separate thermometer is still useful for checking the temperature near plants and spotting differences between its reading and the thermostat probe.

Do You Need a Thermostat for a Greenhouse Heater?