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Best Greenhouse Heaters for the Cold Season

Best Greenhouse Heaters for the Cold Season

Table of Contents

A greenhouse is an invaluable thing to have for your tender plants during the winter. The best time to prepare your greenhouse for the coming winter months is to install a greenhouse heating system during fall. Heating a greenhouse is imperative when you want to maximize the potential of your plants during the cold winter season. We will show you the best greenhouse heaters in this article so that you can grow your favorite plants year-round!

You might be thinking that installing a heater in your greenhouse could be expensive. On the contrary, choosing the right heating design and equipment is affordable. For growers, the right heating equipment quickly gives them an ROI.

It goes without saying that adding heating to the design of the greenhouse is smart. However, an existing greenhouse can still be refurbished with a heater that does not have to rob the bank. As mentioned, the right heating product goes a long way in providing a comfortable greenhouse environment for you and your plants during winter.

How to pick the right greenhouse heater?

There are a few factors that play a role in deciding for the right greenhouse heating system:

  • What size is your greenhouse?
  • How cold does it get in your location?
  • What resource is the cheapest/most affordable option in your area?
  • How well is your greenhouse insulated?
  • How many plants do you want to grow?
  • What type of plants are you going to grow?

Different plants need different temperatures to survive. Some love the warm weather and some are cool-weather crops. So, deciding on the heater has a lot to do with how you want to use your greenhouse. Plants actually create heat as well. Is your greenhouse going to be filled with plants or are you going to utilize only a fraction of the growing space?

With this being said, you have to think about how you are going to manage your greenhouse in winter. Otherwise, you cannot make the right choice for heating your greenhouse.

Let’s say, you are growing only hardy plants and you are using most of your greenhouse. Then either a DIY heating system (thermal mass) or a small space heater may be sufficient. If you have a larger greenhouse, you are not fully using it during the cold season and the temperatures get very rough in your area, you might need a greenhouse heater that can keep up with these conditions.

The size of your greenhouse also plays an important role in choosing the best type of heater. Make sure that the greenhouse is properly insulated so that the heat won’t escape.

You don’t necessarily need a heater if:

  • Insulation is top-notch
  • Mostly (cold-)hardy plants (no cold-sensitive plants) and you’re using your space well
  • Used some DIY heating ideas (e.g. thermal mass, heat-absorbing rocks, greenhouse installed under frost line)

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A heater in a greenhouse and a greenhouse surrounded by snow and the text: Best Heaters - How to keep your greenhouse warm

Which type of greenhouse heater should you pick?

The most common heater types are electric and gas. Most gardeners prefer gas heaters because they are affordable, especially in their local area. It uses natural or bottled gas. Gas heaters have the same effects as electric heaters. You simply need to install sufficient ventilation in your greenhouse because it may emit a significant amount of fumes. Confined fumes can be bad for you and your plants’ health.

The electric heater is so popular because of its efficiency in keeping warmth at a consistent level. It does not release any dangerous fumes. This is best for those greenhouses with insufficient ventilation. It might be best, but it is also the most expensive of the three.

Paraffin is the cheapest manual heater that anyone can buy from a local market. The fuel used is also affordable although it is a bit hard to find these days. It also gives off carbon dioxide which is needed by your plants.

How many BTUs do you need?

Ok, so this is a tricky question because – again – this depends on the greenhouse size (including height), insulation and greenhouse usage. 

Theoretically speaking, 10,000 BTU is supposed to cover 400 – 450 sq.ft and 20,000 BTU around 1,000 sq.ft. However, this is for houses with insulated walls. A greenhouse does not have that much insulation. The R- or K-Value of your greenhouse model will give you an idea of how well insulated it is (not every model mentions this in the description). If you want to read more about greenhouse insulation, check out this article!

Then you also have to keep in mind the lowest temperatures in winter and what climate you want to create in your greenhouse.

Let us give you the extreme: Our biggest greenhouse is 16ft x 30ft and comes with a 30,000 BTU commercial gas heater. It is well insulated but not as good as the RIGA XL greenhouses. However, it’s enough to heat the space up in winter. This example may give you an idea of what you need for your situation.

Electric greenhouse heaters

There are several upsides to electric heaters, foremost of which is to provide a steady temperature to your greenhouse. They come in different types. Tubular electric greenhouse heaters use a heating element to distribute warmth to the entire area. The lower electric consumption by omitting the need for fans. Fan-assisted models have a fan that radiates heat to specified areas

Pros:

  • Effortless to use
  • Electricity is readily available (for most people)
  • Doesn’t need to be refilled
  • Thermostat for easy control over temperature (no overheating or freezing)
  • Provide a tightly controlled temperature to a specific area
  • No toxic fumes

Cons:

  • Heat may not be distributed evenly in some cases (some plants may get too much heat and others may freeze)
  • Setting up electrical wires (if not there yet)

Top electric heaters for your greenhouse

White RSI greenhouse heater with the features

For medium to large greenhouses: RSI Greenhouse Heating System

  • 17,000 BTU
  • Includes two heat settings
  • Frost watch function is one of its best features
  • Guarantees the right temperature with the built-in thermostat feature
  • Switches off if overheating
  • Doesn’t take up surface space: Easily hangs from rafters or ceiling
  • Includes installation hardware and mounting bracket

For small to large greenhouses: AirNmore Infrared Space Heater

  • 1500W
  • Uses Copper PTC as the heating element
  • Touch safe: Shell doesn’t heat up
  • Tip-Over Sensor
  • Two heat settings (1000W and 1500W)
  • Fast heating
  • On castors
  • Up to approx. 800 sq.ft. (if insulated well)
  • Heavy-duty particle filter

For small greenhouses: 1500W Ceramic Space Heater with Adjustable Thermostat

  • 1500W
  • 130 sq.ft.
  • Fast heating
  • Choose from three heater modes with fan
  • Adjustable thermostat
  • Quiet and easy to use
  • Automatic overheat system 
  • Tip-over switch: Unit shuts off automatically

Gas greenhouse heaters

Using gas to heat your greenhouse can be practical because it doesn’t require a power source. So, you don’t need to lay a cable. The problem with using gas, propane, and butane are the toxic fumes it emits. However, the requirement of high temperatures can be quickly accessed because of their built-in thermostat control.

Pros:

  • Effortless to use
  • A thermostat easily controls the temperature of the greenhouse
  • High temperatures are easily accessed
  • No power connection needed
  • The traditional way of heating

Cons:

  • Condensation problems are expected
  • The fumes emitted may be toxic
  • Needs a spare cylinder on hand at all times
  • Needs refills of gas bottle

For medium to large greenhouses: Mr. Heater Corporation

  • 20,000 BTU
  • Up to 500 sq. ft.
  • Blue flame
  • With thermostat
  • Battery-powered electronic ignition
  • Automatic low oxygen shut-off system (ODS)
  • Can stand on legs or be mounted on the wall

For medium to large greenhouses: Dyna-Glo 18,000 BTU Cabinet Heater

  • Heats up to 450 sq. ft.
  • 8,000-18,000 BTU
  • Heats up to 64 hours using a 20 lb. propane tank
  • Oxygen depletion sensor
  • Tip-over protection
  • Portable: Locking castors

Small greenhouses: Dyna-Glo Natural Gas

  • 5,000-10,000 BTU
  • Propane only
  • Blue flame convection technology
  • Heats up to up to 300 sq. ft.
  • Customizable heat settings

Solar-powered greenhouse heaters

Greenhouse heating can cost a lot of energy consumption with the use of pumps and devices as well as maintaining the right temperature. Solar panels seem to hold the correct answer for serious gardeners who want to keep optimum plant growth and development. The use of solar panels to maintain a steady temperature throughout the year makes both plants and environment healthy and happy.

While any type of solar panels can be used for your greenhouse, the more efficient ones are the monocrystalline solar cells and the polycrystalline solar cells.

Polycrystalline solar cells

Pros:

  • Silicon waste is avoided
  • Effects on efficiency are not negatively affected by hotter temperatures
  • More affordable option than the monocrystalline cells

Cons:

  • The low purity levels of silicon do not make them an efficient solar panel option
  • They are less space-efficient because of their lower output rates. Installing them means more roof space

Monocrystalline solar cells

Pros:

  • High-efficiency rate of 15-20% that requires less space
  • The usual warranty is for 25 years because manufacturers believe in the long lifespan of the solar cells
  • Works efficiently even on cloudy days because they have always shown peak performance even on low sunlight levels

Cons:

  • Very expensive, in fact, the most costly solar cell available on the market
  • A rise in temperature can sometimes affect the levels of their performance
  • Manufacturing them leads to a lot of silicon waste

Do you have any other questions about heating your greenhouse? Let us know in the comments!

18 comments

  1. Jerry Rombach

    In our area of Alaska I need a solar heater system for summer! We get lots of sunlight (21 hours), but even so the nighttime temps can get into the 30s – an inside temperature swing of 70 degrees. I have no electricity to this small greenhouse – 120 sf. Is my best bet contacting the local commercial/residential solar energy provider?

    1. Greenhouse Emporium

      Hi Jerry, yes that would be your best bet. I assume not many shops ship for free to Alaska and there are probably local providers that offer great solutions.

  2. I have purchased a 8×12 greenhouse(polycarbonate windows) that is being delivered tmrw. I live in NJ and will be storing my palm trees in there for the winter. What temp. Is optimal for the winter and how much watering will be needed. Could you recomend a heater. Also, do I need a circulation fan or vent?
    Thank You,
    Tom

    1. Greenhouse Emporium

      Hi Tom, there are plenty of recommendations in the article. You want to go for a heater that we recommend for medium greenhouses. Then you have to decide what power will be best for your local area (cheapest or most convenient). Palm trees are tropical so you want to keep it warm but you should check for the hardiness temperature of your plant species. This will give you a better idea of how warm you need to keep your greenhouse. For watering, again, it depends on the plant. Regular watering like indoor plants will be required. You don’t need a circulation vent. Your roof vents etc should provide airflow but it will be more humid in there (it’s a greenhouse after all). If you want less humidity, you want to get an exhaust fan.

  3. Jacqui Carroll

    Greetings
    I have a 20’x14’ greenhouse that has a south facing slant roof of single polycarbonate. The north ceiling and wall are well insulated.
    We had determined that a 36,000 btu gas heater would b more than adequate to heat with.
    We have a spare 75,000 btu gas heater that is available to use.
    Can we use this heater? Is it overkill? The extra space it will take up is not an issue. I am on a limited budget, so it would be great if I could use this unit and not have to buy a new one.
    Thank you

    1. Greenhouse Emporium

      Hi Jacqui, I’d say go with what you have available. As long as it has a thermostat, you should be fine. This way you can test it this winter. If it’s too much (too hot or too much gas cost), you can always get a smaller one next winter.

  4. Do you recommend oil filled heaters for a 6×9 greenhouse?
    Thanks!

    1. Greenhouse Emporium

      Hi Charly! If you let it run constantly and don’t have tropical plants in there, it will likely work. 6×9 isn’t a big greenhouse so it doesn’t require much heat. However, we have never used this type of heater or heard of experiences from customers. So, I don’t want to bring you into trouble.

  5. Hello..
    We are putting up a 18×36 greenhouse and trying to determine the right heater to install. Can you recommend what BTUs I should be using, electric or gas? Thank you..

    1. Greenhouse Emporium

      Hi Tara, you would need a commercial/industrial heater because that’s a large area to heat. In the article, the only product we recommended for that size is the “AirNmore Infrared Space Heater”. However, if your greenhouse isn’t well insulated, you may need a more powerful heater (20,000-30,000 BTU I’d suggest). When deciding between gas or electric, it’s really your own preference and which one is cheaper for you.

  6. Gail Nelson

    I have a 10 x 12 x 10’3” polycarbonate greenhouse. Can you please recommend what size heater I should be purchasing? I have not decided what type to use. Can you give me the pros and cons of propane vs electric?

    1. Greenhouse Emporium

      Hi Gail, we have size-related information under each heater. Please check it out.

  7. Hi! I have a medium sized greenhouse that was built off the side of my house. It has a wood frame and single pane windows. We’ve been trying to seal up any cracks and gaps that we’ve found to make sure no heat is getting out. I keep most of my indoor plants (tropical plants and succulents) in there and I’m worried that it’s not going to stay warm enough this winter. Right now we have an electric, oil filled heater but I think it is too slow in heating up the area. Should I get a fan to blow the heat around or do you think there is a better type of heater for my type of greenhouse?

    1. Greenhouse Emporium

      Hi Stacy, a fan will certainly help to move the warm air around. However, if you have the feeling that it’s not even getting hot enough close to the radiator, I’d just get a new heater that has a fan included.

  8. Hi! I’m thinking about using a 12’x12′ bubble tent as a greenhouse and using an oil filled radiator space heater in it. I intend to start seeds of mainly flowers and a few vegetables. I live near Chicago and it can get quite cold here. Any thoughts on my choice of greenhouse and heater? Thanks!

    1. Greenhouse Emporium

      Hi Cathleen, it’s hard to say without knowing much about the bubble tent but for the size, a radiator like that might be sufficient. Let us know how you got through the first winter. We are always interested in the experiences!

  9. Sheri Bethard

    Our Master Gardener organization has a 30×40 hoop style greenhouse. the height in the center at the highest is about 15 ft. We are in SE Texas and hopefully the temps won’t get as low as they did recently in the future. Our greenhouse is made of 6 ply poly with polycarbonate single wall ends. It is not well insulated. We are looking for an electric heater(s) to heat our space. During this last hard freeze, we had 4 space heaters working but we still lost a lot of plants. I have looked at Modine, DR Infared Heaters, Phoenix Greenhouse heater and Bio Green heaters so far and trying to figure out which one would be best for us is a quandry. Can you give us any suggestions on electric heaters that will heat our space. If we can keep it around 55 degrees that would be fine.

    1. Greenhouse Emporium

      Sorry to hear that you had such issues! So from your message, I can read that you have a very very large greenhouse with lousy insulation. So, you would need something for commercial purposes or something that can heat a space as big as 500 sqft big (4x your sq ft). Now, most of these are wall or ceiling mounted which you cannot do in a hoop house… I see your problem. This is tricky and I would have to do more research on this because we usually don’t deal with hoop houses or DIY greenhouses. I don’t think you’ll find a “one heater solution.” It’ll likely be at least 2 heaters. I’m sorry that I cannot be of much help but I will do my best to add more value to the article as soon as I can so you (and other people that share the same issue) can find a better answer.

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