Does a Greenhouse Need a Heater: Gardening Solutions

As the temperatures start to drop, you may be wondering if you need to install a heater in your greenhouse. After all, you want to provide the best growing conditions for your plants and vegitables. So, does a greenhouse need a heater?

A greenhouse does not need a heater as it is designed to trap heat from the sun. However, if the temperature is below 50 degrees Fahrenheit then the introduction of an additional heat source may be needed. Extra heating will depend on what you are growing.

In this blog post, we’ll explore the answer to that question and provide some tips on how to keep your plants warm during colder months.

Does A Greenhouse Need A Heater?

A greenhouse needs a heat source, it doesn’t always need a heater to maintain the ideal temperature for plant growth. The sun will provide the majority of the heat for a greenhouse, but in winter months or during periods of cloudy weather, you may need to supplement the sun’s warmth with a heater.

Greenhouses are designed to trap heat inside, so a small heater can go a long way. The size and type of heater you’ll need depends on the climate where you live, the size of your greenhouse, and what kinds of plants you’re growing.

There are many ways to heat a greenhouse, some of the more common ways to heat a greenhouse include:

• The sun
• Solar Panels
• Mini Wood Stove
• Propane Heater
• Electric Radiant Heater
• Compost
• Hydronic heating

Related article:

• Why Do Plants Grow Faster in a Greenhouse than Outside
• Do Greenhouses Need Ventilation
• 5 Best Heaters For Greenhouses

Does a greenhouse need a heater in the winter?

A greenhouse does not necessarily need a heater in the winter, but it depends on the climate and plants inside.

Heaters can be used to control the temperature and humidity levels in a greenhouse. If you live in an area with a mild climate, your plants may do just fine without a heater.

But if you live in a colder climate, a heater can help keep your plants warm and protect them from frost.

How much heat does a greenhouse need?

The amount of heat a greenhouse need depends on a number of factors, including the type of plants being grown, the climate, and the time of year. In general, greenhouses require more heat in the winter and less heat in the summer.

When a greenhouse reaches a temperature of about 90 degrees Fahrenheit, it is considered too hot for your crops. Even the most hardened of sun-loving plants won’t be able to stand this level of heat.

• During the day, a greenhouse’s ideal summer temperature is 75-85° F, with 60-76° F at night.
• In the winter, it ranges from 65-70° F during the day and 45° at night.

The temperature can be controlled most effectively by ventilation, shade cloth, and heating.

At what temperature do you need a heater in a greenhouse?

As you can imagine, this answer largely depends on the plants you are growing, how well insulated your greenhouse is, and the outside temperature.

Summer: Greenhouses typically perform best when the temperature is between 75-85° F throughout the day and 60-76° F throughout the night.

Winter: Greenhouses typically perform best when the temperature is between 65-70° F throughout the day and around 45° throughout the night.

You will want to keep your plants at a stable temperature throughout the night and day.

If the outside temperature is too cold, for example, there is frost or even snow on the ground, then its likely you’ll require a heater to help maintain the heat inside the greenhouse.

• If you find that temperature to drop you can use a heater to supplement the heat.
• If it becomes too hot then you could use an exhaust fan to help vent and circulate some fresh cooler air.

If you are growing sun-loving plants, such as tomatoes then it’s best to keep the greenhouse during the day at around 80° F. If the temperature drops below 50° F then you will need the help of additional heating to maintain the temperature.

This table is from a U.S. Department of Agriculture Research Service report, it shows the optimal temperature to grow tomatoes based on the light and temperature conditions. It also shows the upper and lower ranges where the tomatoes won’t grow as well.

Stage of growth	Light	Lower optimal Temp (° F / ° C)	Upper optimal Temp (° F / ° C)	Lower failure Temp (° F / ° C)	Upper failure Temp (° F / ° C)
Seedling/ Early	Any light	24 / 75.2	26.1 / 78.9	9 / 48.2	35 / 95
Vegetative	Sun	24 / 75.2	27 / 80.6	10 / 50	40 / 104
	Cloud	22 / 71.6	24 / 75.2	10 / 50	40 / 104
	Night	18 / 64.4	20 / 68	10 / 50	40 / 104
Producing fruit / Mature	Sun	24 / 75.2	27 / 80.6	10 / 50	40 / 104
	Cloud	22 / 71.6	24 / 75.2	10 / 50	40 / 104
	Night	18 / 64.4	20 / 68	10 / 50	40 / 104

Do small greenhouses need a heating system?

If you feel the temperature is too cold, then the addition of a small heater might be what your plants need for optimal growth.

You can track the temperature with a thermostat to determine if a heater is needed.

How do you keep a greenhouse warm without a heater?

There are a few ways to keep a greenhouse warm without a heater. One way is to use thermal mass. This can be done by filling containers with water and placing them in the greenhouse.

The water will absorb the heat during the day and release it at night, helping to keep the greenhouse warm.

Another way to store heat is to use black or dark colored materials inside the greenhouse. These materials will absorb heat during the day and release it at night, helping to keep the greenhouse warm.

Finally, you can insulate your greenhouse to help trap heat inside. This can be done by adding extra layers of plastic or using bubble wrap on the inside of the greenhouse.

By doing these things, you can help keep your greenhouse warm without a heater.

Related article:

• Does a Greenhouse Need a Clear Roof
• Can a Greenhouse Be in the Shade

What is the cheapest way to heat a greenhouse?

There are a few things to consider when trying to find the cheapest way to heat a greenhouse.

The first is the size of the greenhouse. A small greenhouse will obviously require less heat than a large one. To know how much heat your greenhouse needs, you will need to use a BTU calculator to find out how many BTUs are needed to heat the size of your greenhouse. We have a BTU calculator here.

The second consideration is the type of heating you plan to use. Electric heaters are typically the most expensive option, while wood or propane heaters are usually cheaper. If you live in an area where natural gas is available, that can also be a relatively inexpensive option for heating a greenhouse.

The third factor to consider is the insulation of your greenhouse. A well-insulated greenhouse will require less heat to maintain a consistent temperature, which will save you money in the long run. You can check the insulation of your greenhouse by doing a simple heat loss calculation.

Finally, you should also consider the cost of the fuel you will be using to heat your greenhouse. If you are using a propane or natural gas heater, the cost of the fuel will be a significant factor in the overall cost of heating your greenhouse.

In general, the cheapest way to heat a greenhouse is to use a wood or propane heater. You may also want to consider alternative heating such as compost and Hydronic heating which can be a free source of heat in some cases.

Is a Greenhouse Heater right for you – What zone are you?

The answer could depend on which of the zones in which you intend to grow. In the United States, regions are divided into 13 major Zones based on minimum temperature, with Zone 1 being the coldest and 13 being the warmest. Zones 1 through 4 can reach temperatures as low as -50 degrees Fahrenheit and up, which makes for some pretty frosty foliage.

In cases like these, many at-home farmers are looking to sustainable and effective solutions for their temperature woes by means of electric, wood, gas, and industrial heaters.

Zones 8 through 13 can experience overheating in the spring and summer, causing a decrease in plant production and growth. Warmer climates and even more temperate ones can feasibly sustain a working and fully insulated greenhouse which would render a heater obsolete, or even dangerous to our little green friends. Though plants do need heat to survive, too much of a good thing can always lead to a bad one. In zones like these, composting, insulation, and coverings can make a big difference to your plants without the additional costs and stressors of a managed heating system.

Keeping in mind that a greenhouse is a mirco-climate all its own, fully managed by you.  It’s important to research what plants you intend on growing to know the overall heat requirements they are going to need to really thrive. Once you have that, applying what you know about your area and the heat management methods you already have in place can help you make the leap one way or another.

If you are growing fruits, vegetables, herbs, or plants that thrive in a heated environment then you will probably need to consider a greenhouse heater, especially if you are looking to grow over the winter months. I reviewed my top 5 best heaters for greenhouses for all sized greenhouses – so if you are thinking about getting one then it’s worth checking out.

So How Many Kinds of Heaters Are There Really?

On the market right now, there are dozens of efficient heaters to choose from, all with their own requirements and perks. Doing your research on your plants and knowing what your desired outcome is will help you make a choice based on your and your sproutlings needs.

• Paraffin Heaters-  Paraffin heaters are an affordable go-to for the avid traditionalist. They offer reservoirs that allow them to run without constant maintenance and don’t typically require a source of electricity.  Sizes vary to allow for different requirements to be met based on the greenhouse type. Unfortunately, the fuel isn’t as common as it was back in the day, which means the cost for running them may outweigh the affordability of the unit depending on your area. Paraffin heaters also emit water as they run, which can promote mold and excess moisture in the greenhouse, but can add much-needed humidity to the right set of plants.

• Electric Heaters- Electric heaters seem to be the most common aside from the more natural heating methods. These units tend to be reliable as long as they have power, and can be paired with more renewable sources of energy such as solar or wind. Most workshop and greenhouse electric heaters have fans included, which allows for consistent air circulation. It goes without saying that these kinds of heaters need to be plugged in, so proximity to an outlet is of the utmost importance with these. Knowing the wattage, the output, and the pricing can all be factors of choosing an electric heater fits best for your setup. Electric heaters can be a little pricey, but with the added potential of a connected thermostat, these little guys can offer a more hands-off heating approach.

• Propane and Gas Heaters- RIght off the bat and much like woodstove heaters, these heaters offer convenience separate from a connected outlet. Burning propane and gas produces and encourages the absorption of CO2 in your plants, encouraging growth and production. The source of fuel for these can be purchased in bottles and tanks, making it an accessible and easily attainable source of power in setups with little to no electric culpability. These machines can be a little expensive depending on the size, so having a vision for where it’s going and how it’ll be positioned might help save a few bucks upon purchase. All in all, these are stable and safe heating options.

• Wood and Coal Heaters- The concept of a wood stove in a greenhouse can seem a little off the wall on first glance. With these heating systems, a more monitored approach is generally recommended and the heat can be inconsistent without proper fire maintenance since once the fire dies, the heat dissipates quickly. Meant to be used in well-insulated and well-maintained enclosures, these heaters provide a natural bug and pest repellent by means of the smoke produced. The wood and coal ash contain potassium and lime, which is an excellent additive to any fertilizer. These systems are easy to DIY and with enough attention, love, and care, they can add a little fire to your gardening experience.

Related article:

• Do Greenhouses Block UV Rays

Greenhouse Heating Alternatives

Based on all the factors listed above, at this point, you may have decided on coming up with a more natural or self-managed heating system. Though these systems are not infallible, using some or all of them can help to get you a few steps closer to a toasty greenhouse set up, even when it’s frigid outside. In most, if not all of these systems, a hearty insulation setup is highly recommended for heat retention once it’s gathered. Generating heat is one thing, but keeping it in a way that’s useful is another.

• Heat Sinks- Commonly known as thermal masses, heat sinks are a great way of gathering solar heat using a tank of water and a jug. Typically, the tank of water is approximately 55 gallons, and the jug can be as simple as a painted milk container. This works when the jug is painted black and therefore absorbs the heat, and much like a swimming pool in the summer, the water’s temperature rises over time. At night, the heat is still retained and is released as the outside temperature drops. This cycle repeats as long as there is solar heat during the day.

• Composting-  Compost heating systems, also known as Biomeilers, heavily rely on composting as a means of generating heat energy. Composting is a beneficial way of reducing waste while repurposing that energy for growth. This generally works as a DIY project that includes a wooden or plastic box with a means of closing. Based on a general composting consensus, a sure-fire way to begin a fully functional compost bin is to combine two parts of a “brown” component, which may include wood chips, newspaper, sawdust, and/or dry leaves with one part “green” component (ie discarded veggies, grass clippings, coffee grounds, etc.) and water. As the concoction breaks down, heat is released and can be reused if harvested correctly. Many at-home gardeners stack compost between rows of plants to evenly distribute the warmth, though it should be mentioned that as the components break down, the release of heat will slow over time. Keeping a constant temperature will mean a renewal of the compost as the materials decompose, which can be a little more hands-on in comparison with other systems.

• Radiant Floor Heating- While technically this method does include an external heat source like a boiler, this means of heating a greenhouse can be considered alternative as well as it can be paired with any other method on the alternative list. This process includes running pipelines beneath the floor filled with warmed water. This heats the pipes, which warms the ground. It can be an expensive way to go upon installation, but one that will last years if done correctly. There are also a ton of DIY opportunities for the particularly savvy with this one, and offers a mostly automated means of heat generation.

• Solar Energy Farming- Clean energy is a huge selling point for many of today’s avid farmers. Using solar panels, one can power an electric heater on the inside of the greenhouse, allowing for all of the perks that come with the electric heater, minus the costs of power. Start-up on solar can be a pretty penny up front, but also has the potential to pay for itself over time. Solar in general can be used without an additive, so long as the area allows for direct sunlight into the enclosure.

• Wind Power- Much larger than most backyard planters have the time or space for, wind-powered turbines are a great source of renewable power for larger setups. Having the option for harvesting wind energy means a little bit of an investment up front, a wide-open space for these to work to their full potential, and basic maintenance. Definitely not for the faint of heart, or recommended for beginners!

Wrap Up

So, does a greenhouse need a heater? Even though it seems counterintuitive, greenhouses do not necessarily need heaters to stay warm. Greenhouse growers often rely on the suns solar heating to keep their plants comfortable year-round.

However, if your plants are not well suited for certain cold conditions then you may need to provide some supplemental heat.

Rob Jones

Rob is an enthusiast of all backyard DIY projects. He has spent many years researching, learning, and building. From a backyard shed to a garden pond, Rob will have done it!