How to Heat a Greenhouse: 8 Effective Methods


Heating your greenhouse during winter or cold nights can be tricky or expensive. Luckily, there are many methods to heating a greenhouse that are safe, environmentally friendly, cheap, or even free.

To heat a greenhouse, consider the use of composting, insulation, or an electric or rocket mass heater. Some people have had success with bubble wrap and gas heaters, or you can also use the sun’s energy to your benefit through thermal mass and heat sinks for a more environmentally friendly option.

This article will discuss the many methods of heating a greenhouse at night or during the winter, as well as options that are free or cheap, natural, and don’t require electricity. We’ll also discuss the use of solar energy and composting.

Photo of a space heater inside a greenhouse
Photo by Evgenii Mainagashev

How to Heat a Greenhouse with Solar Energy

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Utilizing the sun’s energy to grow your plants is the whole purpose of a greenhouse. However, this is a difficult task in the winter and at night. Luckily, there are many ways to use the sun’s energy for those colder periods, including adding thermal mass, a rocket mass heater, a heat sink, or insulation.

Insulate

The most important way to keep your greenhouse warm is to ensure that heat doesn’t escape. This is tricky with greenhouses, as their walls are transparent, making it easy for solar energy to both enter and escape.

Insulating your greenhouse will reduce the amount of heat that escapes, and there are two common ways to go about this.

  • The first method is to use bubble wrap. Bubble wrap is transparent enough that it does not block the sun’s energy but will still keep that energy inside. Bubble wrap also covers up the cracks and gaps in your greenhouse’s structure, preventing cold air from coming in and heat from escaping.
  • The second method includes using weatherproof tape to seal all the cracks and gaps that allow heat to escape. You can use this method alone or tape together sheets of bubble wrap or other insulation types.

Create a Heat Sink

A heat sink uses dense material such as rocks, cob, and bricks to store and trap heat underground. This underground pit gathers heat throughout the day and radiates it back into your greenhouse when the air is cold.

To create a heat sink, you will need to dig a large hole near the center of your greenhouse. A standard 10′ x 10′ (3.05 x 3.05 meters) greenhouse will only require a 3′ x 3′ (91 x 91 cms) heat sink. After digging your hole, fill the heat sink with materials that easily absorb heat, such as bricks, concrete, or gravel. The final step is to add piping to your heat sink to ensure that heat rises into your greenhouse.

Add Thermal Mass

As with the heat sink method, adding thermal mass to your greenhouse will keep it warm through colder periods. Thermal mass includes water, concrete, soil, bricks, or gravel. Many of these materials might already be in your greenhouse, so you might not need to go out of your way to get them.

The reason this method works so well is that all these materials absorb more heat than air. Below is a table that shows how much heat each material absorbs compared to air.

MaterialAmount of Heat Absorbed Compared to Air
Water4.23x
Wet soil1.49x
Stone1.01x
Concrete1.01x
Dry soil.81x

This table makes it clear that packing your greenhouse with plenty of water, soil, and building materials will help keep your greenhouse warm throughout the day and then into the night.

Face Your Greenhouse Towards the Sun

If you haven’t built your greenhouse yet, make sure to plan on positioning it so that it faces towards the sun. If you’re in the northern hemisphere, you should orient your greenhouse towards the south and southeast.

Due to the Earth’s tilt, the sun shines on the northern hemisphere from a southern angle. This means that the southern half of your greenhouse will receive more heat and energy than the northern half. Therefore, you should utilize the southern part of your greenhouse more for natural heat sources with little to no effort.

Using Solar Panels

If considering using an electric heater to keep your greenhouse warm in the winter months, you might want to look into purchasing a portable solar panel and battery storage. While a bit more expensive than gas heaters at first, this option is more environmentally friendly and can help you save money in the long run by saving on buying gas.

How to Heat a Greenhouse with Compost

Compost is a great way to generate heat in your greenhouse. This is a natural method of breaking down organic material to create nutrient-rich material for your plants. Composting naturally creates a good amount of heat and, therefore, can be utilized as a natural “heater” for your greenhouse.

How Composting Works

All organic material decays. When you throw away old food, it will slowly decompose due to all the microorganisms in the environment that feed off it. Decomposition is a process that has been going on for almost as long as the Earth has been around.

Composting speeds up the decomposition process. Compost bins create the perfect environment for these microorganisms to thrive. With more microorganisms, there is more decomposition. The result is nutrient-rich soil that will make your plants healthy and happy.

But composting isn’t just great because it creates nutrient-rich soil. The breakdown process generates an enormous amount of heat. That heat not only keeps this environment perfect for more composting (microbes love high temperatures) but also naturally warms up your greenhouse.

The Components of Composting

To get the most out of your composting pile, you need to ensure you have the right amount of each of the following:

  • Organic matter, both green and brown
  • Moisture
  • Oxygen

Your green organic matter may consist of food scraps and grass trimmings, where the brown matter may come from dried leaves and even wood chips. It is important to have both to maintain the proper balance within your compost pile.

Similarly, too much or too little moisture and/or oxygen will hinder the decomposition. Bacteria require both to thrive, but too much will drown or dry out the process. It is important to toss your compost so that the moisture and oxygen can evenly distribute, even to the bottom of the barrel.

Benefits of Composting

You will probably notice that compost comes up multiple times in this article. That’s because composting is natural, free, easy, and long-lasting. It’s the best method to keep your greenhouse warm, especially if you are avoiding any method that uses electricity.

Since you are already composting to create nutrient-rich soil for your plants, you don’t need to spend extra money on the process, making it technically free. Composting is also super easy, as all you have to do is add organic matter to the bin and then aerate the pile occasionally. The microbes do all the work for you.

Although compost bins speed up decomposition, the process can still take months, depending on the amount and type of material decomposing. This means you have a great source of heat for months at a time (which is helpful during the winter). And since you will never run out of organic matter, you have an infinite source of heat and soil.

Different Types of Composting

There are a few different options for composting, and some are better than others when looking to generate heat for your greenhouse. These methods include:

  • Aerated (turned) windrow composting: this is a large-scale method used by companies and restaurants in which they lay their compost in rows (windrows) that sit up to eight feet tall.
  • Onsite composting: also known as “open-air composting,” this method is typically used outdoors and involves creating a communal composting pile with no frame or bucket.
  • In-vessel composting: as the name would suggest, in this method, your compost is contained in a vessel, like a drum or barrel, which is mechanically rotated to turn the compost in place.
  • Tumbler composting: similar to in-vessel composting, this method keeps your compost contained in a vessel, but you will need to turn the compost yourself.
  • Vermicomposting: using red worms to increase the decomposition, this method is usually small scale and is better suited to apartments or in-home composting.

In-vessel or tumbler composting would be your best options when looking to include a composting pile into a greenhouse. The size of the container varies, meaning you can get one that fits your space, and the compost can remain tidily in a corner.

Though in-vessel composting units will be slightly more expensive, it is more hands-off as the machine will turn the compost for you. If you’re looking to save money, tumbler composting is cheaper, but you will need to be sure to turn your compost every few days to ensure all of it is getting adequate moisture and oxygen exposure.

How to Heat a Greenhouse without Electricity

Warming your greenhouse without electricity is not only environmentally friendly but also much cheaper. There are three primary methods of heating your greenhouse without electricity: utilizing solar energy, composting, or using a non-electric heater. 

Use the Energy from the Sun

The primary methods of using solar energy are explained above. Heat sinks, thermal mass, insulation, and utilizing the sun’s orientation are all methods that don’t involve any machinery, wires, or electric power. They just utilize the power of the sun to keep your greenhouse warm.

Compost

As mentioned in the previous section, compost is a free and easy way to heat your greenhouse without electricity. All you need to do is fill your compost bin, aerate it occasionally, and let the microbes do their thing. No power is needed.

Use Non-Electric Heaters

When most people think of heaters, they think about the electric kind. Most people are accustomed to space heaters that they plug into their homes. But there are a few other types of heaters that don’t use electricity.

Gas Heaters

Gas heaters are a popular and affordable option for heating your greenhouse. Gas heaters run on natural or bottled gas, such as propane, and are flueless.

Overall, running a gas heater is usually cheaper since you only need to buy gas to refill the heater, and you don’t have to deal with high electric bills. However, they are less effective than electric heaters, so you get what you pay for.

Furthermore, you will need to consider the carbon dioxide and water vapor output if using a gas heater in your greenhouse. Both carbon dioxide and water vapor stimulate plant growth but can cause other problems. If you go with this option, you will need to find a way to release some of the carbon dioxide from your greenhouse so that you don’t get carbon dioxide poisoning.

This method is also not environmentally friendly for that reason, so something to consider if you’re trying to find a greener way to heat your greenhouse.

Another option is to use paraffin heaters that are fueled by kerosene. They are portable, unvented, residue-free, and don’t form any soot. Like gas heaters, they output carbon dioxide and water vapor, which can be great for plants, but not so great for you. As with gas heaters, use with caution.

Photo of a white chair inside of a greenhouse
Photo by Tanja Rosso

How to Heat a Greenhouse Naturally and for Free

Many greenhouse owners want to do things as naturally as possible. And after spending money on plants, building materials for the greenhouse, and all the items that your plants need, you probably don’t want to spend more money on heating materials. Luckily, there are a couple of methods to heat your greenhouse purely with natural products, which we’ve highlighted in more detail above.

  • Compost. Compost is the most natural option to heat your greenhouse, and a great way to reduce your waste. Besides buying a compost bin, this method costs nothing. As an avid gardener, you likely already have a compost bin to create free, nutrient-rich soil for your plants. You can add dead leaves, food scraps, brush trimmings, grass clippings, etc., to your compost. These are all-natural materials broken down naturally.
  • Thermal mass. Many natural products make great thermal mass, but water is the best option. Many greenhouse owners put giant barrels of water in their greenhouse to absorb heat. Other natural options include soil and rocks.

How to Heat a Greenhouse Cheaply

If you don’t like the free options but are still looking for a heating solution on a budget, then the following options might be for you.

Heaters

Heaters can be a cheap way to keep your greenhouse warm, especially if you only use them at night. Though the cost of electric heaters may add up, gas or paraffin heaters might be the solution you are looking for. After buying a gas or paraffin heater, you only need to pay for the cost of gas or kerosene. Though there may be occasional maintenance, these heaters don’t have any additional costs to keep running. But, they are less good for the environment, so while they are cheaper options, you might want to consider greener alternatives.

Bubble Wrap

Bubble wrap is a simple way to keep your greenhouse insulated and warm and it is an excellent option if you need to add insulation to your greenhouse but don’t want to spend too much money.

Other insulation materials can add up, even costing hundreds of dollars, but bubble wrap does the trick for much less. For example, this Uboxes Small Bubble Cushioning Wrap contains 175 feet (53 meters) of bubble wrap for a meager price.

How to Heat a Greenhouse at Night

Depending on the season and which part of the world you are in, you may only need to keep your greenhouse warm during the night. When looking for ways to keep your greenhouse warm at night, you need to generate heat and insulate your greenhouse to prevent that heat from escaping.

Heat Generation

Heaters are the best option to heat your greenhouse at night. Even if you are utilizing the sun’s energy throughout the day, it may not be enough to keep your greenhouse warm once the sun goes down. Therefore, you will need to generate heat to prevent your greenhouse from dropping to freezing temperatures. Gas xand electric heaters would all do the job perfectly.

If you have a large enough compost bin, you may be able to depend solely on that throughout the night. But more often than not, you will need some help from a heater. 

Insulation

Proper insulation will prevent your greenhouse temperatures from dipping too low at night. Even if you have great heat sources such as heaters or a compost bin, that isn’t going to matter if your greenhouse isn’t properly insulated. Whether you use bubble wrap or other insulation materials, you must adequately insulate to keep your greenhouse warm.

How to Heat a Greenhouse During Winter

When planning for the winter, you want ways to heat your greenhouse that will work for a long time. Below are a few long-lasting options.

Insulation

Insulating your greenhouse with bubble wrap or weatherproof tape will keep as much heat as possible inside for as long as possible. This keeps your greenhouse warmer and prevents heat generated from escaping.

Heaters

Heaters are the best way to heat your greenhouse all winter long. Even if using a heater is the last resort, you may need to use one to ensure your plants survive the winter. You should also make sure to insulate your greenhouse well to trap in the heat.

Photo of a heater inside a greenhouse warming the plants
Photo by Антон Скрипачев

How Expensive are Greenhouse Heaters?

The answer to this question depends on the type and size of the heater and the size of your greenhouse. Your heater needs to heat your greenhouse to at least 45 degrees Fahrenheit (7 degrees Celsius). The following table shows how much energy each heater needs to emit to warm up your greenhouse.

Greenhouse dimensionsParaffin heatersGas heatersElectric heaters
6.5 x 4.5 ft (1.98 x 1.37 m)5214 BTUH5214 BTUH1580
8 x 6 ft (2.44 x 1.83 m)6864 BTUH6864 BTUH2080
8 x 8 ft (2.44 x 2.44 m)8184 BTUH8184 BTUH2480
10 x 8 ft (3.05 x 2.44 m)9438 BTUH9438 BTUH2860
12 x 8 ft (3.66 x 2.44 m)10692 BTUH10692 BTUH3240

A gas heater, such as the Mr. Heater F232000 MH9BX Buddy, is an efficient and inexpensive way to heat your greenhouse, costing just under $75. 

This Dura Heat Indoor Kerosene Heater costs a little more, at about $150, but has 360° heating and can go for up to 12 hours on one tank of fuel.

On the other hand, an electric heater is a bit more expensive to run but is far more effective and doesn’t need to be turned off for refills. This Dr. Heater Greenhouse Infrared Heater is portable, lightweight, and designed specifically for use in greenhouses and garages. At a standard 1500W, this little heater can warm a space up to 150 square feet (13.94 square meters) for just over $100.

Gas, kerosene, and electric costs are dependent on how often you need to use your heaters and how much these items cost in your area. In general, gas and kerosene heaters will have more expenses if used daily, as their small tanks will likely only last one night. However, if you live in an area with high electricity costs, you may find that the electric heater is just as costly overall.

Using Solar

If considering using an electric heater to keep your greenhouse warm in the winter months, you might want to look into purchasing a portable solar panel. This Jackery SolarSaga 60W Solar Panel is ideal for powering smaller items and can easily be set up outside your greenhouse. To make the most of the panel, you’ll also need to purchase a battery to store the energy, such as the Jackery Portable Power Station Explorer.

Though this may seem like a high cost at just over $300, when you consider the cost of buying gas or electricity throughout the long winter months, this option should pay off down the line as it will last years and is better for the environment.

Closing Thoughts

There are many creative options to keep your greenhouse warm. Here is a breakdown of all the methods mentioned in this article:

  • Composting
  • Heat sink
  • Thermal mass
  • Insulation
  • Gas or electric heaters

Many of these methods are easy, cheap, and environmentally friendly. Hopefully, this article will help you decide which options are best for your greenhouse. By utilizing one or more of these methods, you will never need to worry about keeping your greenhouse warm again.

Here are Some of my Favorite Gardening Products and Tools

Thank you for reading this article. I hope you found it helpful for growing some new plants in your home or garden. Here are some products I like that I hope you’ll also find helpful. These are affiliate links, and I am compensated for referring traffic. But in all honesty, these are the exact product that I use or recommend to everyone.

Soil: For high-quality soil, I really like Fox Farm Ocean Forest. I do all my growing in containers and this soil has worked great for me. I like how they use nutrient-rich contents like earthworm castings, bat guano, and composted crab and fish.

Fertilizer: Currently I am using a seaweed-based organic fertilizer call Neptunes Harvest. This is a great milder fertilizer option if you want to use something organic. If you want a more powerful fertilizer, I recommend Fox Farm Liquid Nutrient Trio, lots of people have had great growing success with this product.

Pruning Shears: Pruning shears are one of the most useful gardening tools to have because it’s important to prune your plants to keep them healthy. The pruning shears I recommend are the Gonicc 8’’ pruning shears. I like them because they are built sturdy and work both on bigger and smaller plants, so you don’t need to have multiple pruning shears.

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