In the colder months it is essential to maintain the greenhouse temperature to at least 45°F. You can use different types of greenhouse heating systems.
However, what is the cheapest greenhouse heater to run out of all them? Paraffin heater is cheap to buy and is the cheapest greenhouse heater to run.
The paraffin heater itself costs around 100$ and the average price for a gallon of kerosene is 3.58$ in the New York Statewide Region.
The main drawback of this heating system is that it produces water vapor which increases the risk of grey mold development.
So you need to ventilate your greenhouse when burning paraffin which can reduce any savings from running costs.
It is an ideal option if you are mainly going to grow crops at low temperatures and is generally a useful standby heater in case of power shortage.
Do greenhouses need to be heated?
An unheated greenhouse is a perfect place for growing tomatoes and cucumbers in the summer months.
Also, you can grow Chrysanthemums in the fall and alpines, bulbs and hardy house plants including cacti in winter in an unheated greenhouse.
However, if you want to extend a growing season and grow fruit and vegetables in colder months, greenhouses need to be heated.
Do you have to heat a greenhouse in the winter?
It depends on the range of the plants you are going to grown and in what area you are living.
For the ordinary gardener a minimum temperature of 45°F (7°C) should be maintained during the winter.
If the outside temperature is around 28°F (-2°C) in your region you might be able to maintain the temperature of 45°F with these heating tips without using electricity.
However, if the outside temperature falls to 20°F (-7°C) you have to heat a greenhouse in the winter months with any type of heating systems.
Types of greenhouse heating systems
| Type of Greenhouse Heating System | Heating System Specifications |
| Radiant Heating (hot water pipes) | That is the traditional way of heating a greenhouse. The radiant heating works through thermal radiation which transfers in invisible waves through empty space. The objects absorb radiant heat in its path rather than in the air. Water is a heat-transfer medium. A boiler heats the water and a pump circulates it via the tubes. You can install the tubes in the ground for field growing, embed them in the concrete to heat the floor or fit the hot water pipes in greenhouse bench systems. |
| Indirect Heating with air heaters | Indirect heating is a type of open vented hot water system. In this system the hot water is separate from central heating. A coil (heat exchanger) from the boiler heats up the water. For a greenhouse an indirect heating system comprises the CO2 burners with cylinders that heat the air which passes over a naked flame within these cylinders. The burners can run on natural gas, petroleum or diesel. |
| Electric Fan Heater | It works by moving the air over a heat element which then exits the vent and warms up the air in the greenhouse. Go for a model which has a thermostat which switches on and off a heating element. |
| Electric Tubular Heater | It is similar to the hot water pipes but is run on electricity. This system applies the exact amount of heat required at a specific area. You can install the lines of pipes along the greenhouse walls and these will distribute the heat evenly. |
| Electric Convector Heater | It is a heating system which heats the area by warming the air. In comparison to electric tubular heater or electric fan, this system doesn’t circulate the air or distribute the warmth evenly. Although it is a good option to heat the room in the house which you use less often, convector heater is not the best choice for a greenhouse. |
| Electric Heating Cable | There are two types of the electric heating cables: soil-heating cable and air-warming cable. The first one is installed on the staging or in the soil. It ensures that the heat is going where you want it. Air-warming cable clips on the walls of a greenhouse and distributes the heat evenly. |
| Gas Heater | It is a flueless heating option which is run on natural or bottled gas like propane. This one has thermostatic controls and produces CO2 which stimulates the plant growth. Some of the drawbacks include water vapor production and regular maintenance is a must. |
| Paraffin Heater | A paraffin heater is portable, unvented heating device run on kerosene fuel. It consists of the circular wick, burner and a tank filled with kerosene. Lit wick heats the kerosene which turns into gas. This burning gas heats the air through convection and objects nearby via radiation. Go for a blue-flame model and trim the wick regularly. It is a good standby in case of power failure. |
| Linked Central Heating | It is a good option for a lean-to greenhouse or a conservatory. You can install one or more radiators linking them to the central heating. However, most of the central heating systems operate in the day time and shut down at night. You would need to install a separate feed with timer and thermostat. |
How do you size a greenhouse heater?
Apart from being the cheapest greenhouse heater to run, a heater should be large enough to heat the greenhouse to 45°F when it is only 20°F outside.
To find a size of the greenhouse heater that you need, calculate the amount of BTUH (British Thermal Units per Hour).
This formula helps to calculate the amount of BTUH the heater needs to provide for the greenhouse : Surface area x 33 = BTUH.
What size greenhouse heater do I need?
| Greenhouse Size | Paraffin | Gas | Electric |
| 6.5 x 4.5 ft | 5214 BTUH | 5214 BTUH | 1580 Watts |
| 8 x 6 ft | 6864 BTUH | 6864 BTUH | 2080 Watts |
| 8 x 8 ft | 8184 BTUH | 8184 BTUH | 2480 Watts |
| 10 x 8 ft | 9438 BTUH | 9438 BTUH | 2860 Watts |
| 12 x 8 ft | 10692 BTUH | 10692 BTUH | 3240 Watts |
So, for example, if you get a paraffin heater and are going to heat a 6.5 x 4.5 ft greenhouse to 45°F you would need a gallon of kerosene.
A gallon of kerosene provides 135000 BTU which will last for up to 25 hours.
