Heated vs Unheated Greenhouse: Is Heat Worth It? (October 2026)

On this page (11 sections)

1. What is the difference between a heated and unheated greenhouse?
2. When is an unheated greenhouse enough?
3. When is greenhouse heat worth adding?
4. What costs and tradeoffs should you weigh?
5. Can you heat only part of a greenhouse?
6. How should you set up and use greenhouse heat?
7. How does the greenhouse cover affect heating?
8. What common heating mistakes should you avoid?
9. Should you heat a greenhouse overnight?
10. Heated vs unheated greenhouse: how do you decide?
11. Sources

Choose an unheated greenhouse if your crops tolerate its natural winter lows; add heat when measured temperatures fall below the minimum your plants need. The right heated vs unheated greenhouse setup depends on your climate, crops, cover and access to safe power.

An unheated structure can extend spring and fall growing, but it won't hold a fixed temperature. A heater gives you a way to add warmth, though the result still depends on the greenhouse size, cover, air leaks and weather.

What is the difference between a heated and unheated greenhouse?

An unheated greenhouse relies on sunlight and stored warmth, while a heated greenhouse uses an added heat source to support a minimum temperature. Neither option guarantees steady conditions without monitoring.

Sunlight warms the air and surfaces inside a greenhouse during the day. After sunset, heat escapes through the cover and gaps, so the interior can cool quickly.

A heater replaces some of that lost warmth. Its effect depends on the space and how quickly it loses heat, so a heater that suits one greenhouse may not keep another at the same temperature.

Start with the conditions your plants actually experience. A greenhouse thermometer that tracks daily highs and lows can show whether the growing area stays warm enough overnight.

When is an unheated greenhouse enough?

An unheated greenhouse often works for cool-season crops, hardy plants and extending the growing season around spring and fall. It can also shelter plants from wind and some weather, depending on its cover and setup.

Use it to start hardy seedlings, shelter greens or keep potted plants out of direct exposure. Check each crop's temperature needs because a greenhouse can still get too cold for tender growth.

An unheated structure may also suit plants that are dormant in winter. Keep pots from sitting in standing water, and watch for cold nights that could put roots at risk.

The site affects how much warmth the structure collects. A sunny, sheltered spot may hold more daytime warmth than a shaded or windy one.

Use the advice in where to put a greenhouse in your yard when choosing a location.

What can an unheated greenhouse grow?

An unheated greenhouse suits plants that tolerate the temperatures your structure reaches. Cool-weather greens and hardy seedlings are common choices, while tomatoes, peppers and other warm-season crops need warmer conditions.

Don't treat the greenhouse as frost-proof. A thin cover, open vents or a sudden cold snap can leave plants exposed to near-outdoor lows.

Our guide to what to grow in a backyard greenhouse can help you match crops to your setup. If you start seeds early, check the temperature near the trays rather than assuming the whole space is warm enough.

When is greenhouse heat worth adding?

Heat is worth considering when overnight temperatures repeatedly fall below the minimum your plants need. It may also suit seedlings or valuable plants that can't be moved indoors when a cold spell arrives.

Heating is less useful when your crops already tolerate the lows inside. In that case, winter by itself isn't a reason to buy a heater.

First record the coldest readings in the growing area. Then decide whether to heat the whole greenhouse, protect a smaller zone or move sensitive plants elsewhere.

The greenhouse temperature guide explains how targets vary by crop. Use it as a starting point, then compare those needs with your own overnight readings.

What does a greenhouse heater change?

A heater adds warmth when the structure loses heat, and some models also move air. The VEVOR 1500W heater has heating and fan modes, a thermostat, an adjustable angle and overheat shutoff.

This heater suits a grower who wants a portable floor unit for a smaller area and can provide a suitable power connection. Skip it if you need a heater sized and verified for a large, drafty structure, or if you can't keep an electric unit protected from damp conditions.

Heat can be uneven if the heater sits in one corner or airflow is blocked. Give the outlet room, keep plants and combustible materials clear, and follow the heater's placement and use instructions.

How can you control and monitor greenhouse temperature?

Use a thermometer to track temperatures where the plants grow, then adjust heat around the crop target. A thermostat or separate controller can help manage compatible equipment, but probe location matters.

The Inkbird ITC308 is a plug-in controller with marked heating and cooling outlets, a probe and a display that switches between Fahrenheit and Celsius. It can be calibrated and used with compatible equipment.

Choose a controller if you want equipment to respond to a probe reading, or if you already have compatible heating and cooling equipment. Skip it if you only need to observe temperatures, or if the equipment you plan to connect isn't compatible.

A max-min thermometer can show how cold the greenhouse got between visits. The Brannan wall-mounted thermometer and hygrometer tracks high, low and current temperatures, along with current humidity.

This thermometer suits gardeners who want to compare daily highs and lows without adding temperature control. It won't switch a heater on or off, so pair it with suitable controls if you need automatic heat.

Place a controller probe near the plants you're protecting, not beside the heater or against a cold wall. For more on control options, see whether a greenhouse heater needs a thermostat.

What costs and tradeoffs should you weigh?

An unheated greenhouse avoids heater energy use, while a heated one adds an ongoing electricity or fuel demand. The exact cost depends on the heater, run time, local rates and how quickly the structure loses heat.

A small, well-covered growing area may need less heat than a large, drafty tunnel. Sealing obvious gaps and choosing a suitable cover can reduce heat loss, though neither step eliminates it.

Consider what you're protecting and how much space it occupies. Warming a few trays of seedlings may be more practical in a smaller enclosed zone than trying to heat every cubic foot of a greenhouse.

Before choosing an electric heater, check its power requirements and the electrical setup where it will run. Keep connections dry and follow the manufacturer's instructions for use in a damp growing area.

If you can't use the heater safely, stick with an unheated setup or move sensitive plants.

Can you heat only part of a greenhouse?

Yes, protecting a smaller area can be more practical than heating the whole greenhouse. Group plants with similar temperature needs and keep the protected zone suited to your equipment and its safety instructions.

A shelf, propagation bench or enclosed growing area can bring plants together. Don't block airflow or place covers against a heat source.

Use a thermometer at plant level inside the protected zone. A reading near the heater won't tell you whether plants at the far edge stay warm enough.

If you grow different crops, separate those with higher temperature needs from cold-tolerant plants. That can prevent unnecessary heating across the entire structure.

How should you set up and use greenhouse heat?

Set up heat only after you know where it is needed and have checked the greenhouse for drafts and safe power access. A measured target and suitable equipment make it easier to use heat without guessing.

Start by measuring overnight lows at plant level for several cold nights. Group sensitive plants, note the coldest area and compare those readings with the minimums their crops need.

If you add a heater, place it on a stable surface as instructed and keep the unit clear of water, foliage and materials that can catch fire. Leave room for air to move, and don't cover the heater or its air outlet.

Set the control to a minimum that fits the plants in that zone. Check temperatures away from the heater too, then adjust the layout if one side stays colder.

Review the readings after changing a cover, moving plants or changing ventilation. Greenhouse conditions shift with the weather, so a setting that works on a mild night may not be enough during a colder spell.

How does the greenhouse cover affect heating?

A greenhouse cover affects how quickly heat escapes, so check its condition before relying on a heater. Tears, loose edges and gaps can make it harder to maintain a minimum temperature.

Plastic film and rigid panels differ in material and installation needs. Compare options in our guide to greenhouse covers and panels before replacing a worn cover.

For a walk-in structure with a damaged cover, the guide to replacing a greenhouse cover covers the planning involved. Close openings at night when ventilation isn't needed, then reopen them as conditions require.

Don't seal a greenhouse so tightly that moisture and air movement become problems. Monitor humidity and ventilate when weather and plant needs allow.

What common heating mistakes should you avoid?

The most common mistakes are heating without measuring, relying on a single warm spot and overlooking power or moisture risks. Each can leave plants colder than expected or make the setup unsafe.

Don't choose a heater based only on its power rating. The greenhouse's size, cover, leaks and outdoor conditions all affect how well it can hold warmth.

Don't place a thermometer beside the heater and assume its reading represents the whole growing area. Check cold corners and the height where leaves or seed trays sit.

Don't heat plants that tolerate the natural lows just because the greenhouse feels cold to you. Compare the readings with crop needs, and avoid unnecessary heating when the plants are already within their suitable range.

Finally, don't ignore daytime heat or humidity. Ventilate when conditions call for it, and use a fan mode only as directed for the equipment.

Should you heat a greenhouse overnight?

Heat overnight only when measured lows threaten the plants you want to keep there. Daylight may warm the greenhouse, but temperatures can drop after sunset.

Set a minimum based on the crop, not a guess about what feels comfortable. Check at plant height and pay attention to cold corners.

A controller can switch compatible equipment around its probe reading. The Inkbird controller displays Fahrenheit or Celsius and has marked heating and cooling outlets.

A max-min reading helps you understand the overnight pattern. Reset the instrument after checking it so you can compare the next period.

Heated vs unheated greenhouse: how do you decide?

Choose an unheated greenhouse if your crops tolerate the natural lows; choose heat if measured temperatures fall below the minimum your plants need. Let the crops and your readings set the plan.

Pick unheated growing for hardy plants, cool-season crops and seasonal shelter when you can accept winter limits. Skip added heat if the plants are already suited to the lows or you can't run equipment safely.

Choose a heater when tender plants need a warmer minimum and you can monitor the growing area. A smaller protected zone may suit you better than heating the whole greenhouse.

If you're unsure, track overnight lows for several cold nights and compare them with crop targets before buying equipment. Then consider a better cover, moving plants or controlled heat.

For heater options and features, read our guide to greenhouse heaters with thermostats.

Sources

• University of Minnesota Extension: Growing in a greenhouse
• University of Missouri Extension: Greenhouse tomato production

Frequently asked questions

Is an unheated greenhouse warmer than outside?

An unheated greenhouse can warm up in sunlight, but its temperature can fall close to outdoor conditions overnight. The amount of protection depends on the cover, air leaks, stored heat and weather.

Track the overnight low inside before relying on it for tender plants.

What temperature should a heated greenhouse be?

Set a minimum that suits the plants you grow rather than choosing one temperature for every greenhouse. Check the crop's preferred range, then use a thermometer to compare the overnight low with that target.

Adjust heat or plant placement when readings fall short.

Can you heat a greenhouse with a space heater?

An electric space heater can add heat in a greenhouse if it is suitable for the environment and used according to its instructions. Keep it away from water, plants and combustible materials.

Make sure the electrical setup is appropriate for the location.

Does a greenhouse need heat in winter?

A greenhouse doesn't always need heat in winter. Cold-tolerant crops and dormant plants may suit an unheated structure, while seedlings and warm-season plants may need a protected minimum temperature.

Decide from the crops and measured overnight lows, not the season alone.

How do I know whether my greenhouse needs a heater?

Record the greenhouse's minimum temperature over several cold nights and compare it with the needs of your plants. If readings fall below the target, move sensitive pots to a warmer area, add suitable insulation or consider controlled heat.

Recheck readings after making a change.