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Greenhouse Heating Buyer’s Survival Guide

Now that your greenhouse is properly insulated, thanks to last week’s post How to Insulate your Greenhouse, it’s time to consider your options when it comes to heating. Even though greenhouses absorb and retain solar energy, in cool climates a supplementary heating source is still necessary to maintain an environment suitable for growing plants. Installing a heater in your greenhouse will ensure that you can keep growing year round, even during the coldest months. Choosing the right heater for your greenhouse can be a challenge, but it doesn’t have to be. Growers Supply carries a variety of greenhouse heaters and accessories and we want to help you choose the heating system that is right for your needs.

Step 1: Things to Consider

Heating in the winter is one of the biggest expenses of operating a greenhouse, so it’s important to keep a few things in mind when you’re looking at new heaters.

  1. What are the dimensions of the greenhouse?
    The dimensions are important because they help determine the volume of air within the structure that needs to be heated. To get the volume of air, measure the length, width and height of your greenhouse in feet. Multiply the length by width by height to get the volume of air in cubic feet. This volume of air is really important to know so you can get the right size heater.
  2. Modine Hot Dawg Natural Gas HeaterHow large is the growing zone area?
    If you are only using a small portion of your greenhouse as a growing area, it may not be necessary to heat the entire house, especially if there are partitions between your growing area and the rest of the space. Where the growing zone is will also help you determine where a heater should be installed.
  3. What type of film or polycarbonate is on the greenhouse?
    There are several different types of films and polycarbonate sheets that can be used as greenhouse coverings and each has a varying ability to retain heat. Some materials are better than others and it is important to consider how effective your covering is at preventing heat loss.
  4. What temperature needs to be maintained?
    The temperature that you need to maintain inside your greenhouse is important to know because it will affect the amount of BTUs needed to keep your greenhouse at the desired temperature. The difference between the temperature outside and the desired temperature inside directly affects the amount of energy that will be needed to heat your greenhouse. It will take much more energy to make up for a 15° difference than a 40° difference.
  5. Where is the greenhouse geographically located?
    Of course the answer to this question is easy, but knowing where your greenhouse is geographically located will give you an idea of how many months out of the year you will need to heat your house and what the temperature difference will most likely be between the inside and outside. If your greenhouse is in Maine, you will need to heat your house longer and use more energy than someone heating a greenhouse in North Carolina.
  6. How many doors, windows or curtains are there?
    Knowing all the places in your greenhouse where heat can escape easily will help you save money on energy. Think about how when you open a door to a heated building when it’s cold outside. Warm air rushes out. Positioning your heater away from doors, windows or curtains will help reduce heat loss and draw heat across your greenhouse.

Step 2: BTU Breakdown

Modine Power-Vented Natural Gas Heater

A BTU (British Thermal Unit) is the approximate amount of energy needed to heat one pound of water one degree Fahrenheit. BTUs are important in sizing a heater and there is a simple calculation you can use to determine how many BTUs a heater needs to be rated for to work for your application.

First, you need to know the volume of air within your greenhouse. This is measured in cubic feet(c3). Next, you need to know the difference between the lowest expected outside temperature and subtract that from the desired inside temperature. This will give you the change in temperature (∆) from the outside to the inside. Once you have these numbers, use this equation to determine how many BTUs are needed per hour in your greenhouse:

Volume  x  0.133  x  ∆Temperature = BTUs per hour

Step 3: Weigh your Options

Now you’re ready to start thinking about what type of heating system to use. There are many different types of heating systems available and knowing the pros and cons of each will help you purchase the right heating solution for your specific application.

Modine™ Effinity 93 Condensing Unit Heater

Forced Air Heating Systems: These systems are easy to maintain and operate, and are one of the most commonly used heaters in the United States. They are usually controlled by a thermostat and can be powered by natural gas, propane or electricity. Forced air heaters heat by convection. When the temperature in the greenhouse drops below a preset level, the heater kicks on and forces air over a heat exchanger and then moves it throughout the space through ductwork or vent tubing. Using vent tubing with a forced air heating system is a great way to efficiently distribute heat down the entire length of your greenhouse.

Forced air heaters are an excellent choice for both small and large greenhouses as they provide uniform heat for strong and rapid plant growth. They are also extremely energy efficient. The Modine Effinity 93 Condensing Unit Heater is one of the most energy-efficient heaters available, with 93% efficiency.

Radiant In-Floor Heating Systems: These heating systems gently warm a greenhouse through conduction and heat objects instead of the air. These systems contain Pex Tubing which is often installed under concrete slabs or under benches or in soil. Hot water flows through the tubing, heating the mass above it and radiating heat from the ground upwards. This makes it more efficient since the heat emanates from the floor instead of rising to the ceiling.

Radiant in-floor heating systems use a boiler to produce the heated water that flows through the pex tubing and there are several different options available. Boilers like the Quietside Natural Gas Condensing Boiler can provide both hot water and power a radiant heating system. There are also high-efficiency electric boilers like the Hydro-Shark 3™ Electric Modulating Boilers. Another option is a Takagi Tankless Boiler. These boilers are available in propane or natural gas and heat only the water you need instantaneously, providing an endless supply of hot water.

In most areas of the country, if you want to grow year round in your greenhouse, you will need a supplemental heat source to help your plants thrive. Installing a heater that is right for your needs will ensure months of happy growing, even on the coldest days. Choosing a heating method does not need to be a painful chore and now that you’re informed on what goes into selecting a heating source for your greenhouse, it should be a piece of cake.

What methods have you tried to heat your greenhouse?

3 Comments Post a comment
  1. does the greenhouse retain or release heat ?

    February 12, 2013
    • Shaira – During the day during the winter months the greenhouse will retain heat. At night, when it gets cold and the sun goes down the heat will not remain in the structure. Let me know if you would like more information.


      February 14, 2013

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