Most of the heat for a greenhouse comes from the sun, but colder climates require heaters to keep nighttime temperatures from harming plants. Coal, natural gas, propane, oil, electricity, wood, pellets and kerosene are all used to heat greenhouses. Kerosene can be used to heat small greenhouses, but take special precautions.
Find out if you can buy quality kerosene in your area. Kerosene with high amounts of sulphur can damage plants with sulphur dioxide. Also find out if there are building codes in your area governing the construction and use of greenhouses. Often building codes will determine what you can and can't do, including heating your greenhouse with kerosene.
Basic Questions to Ask
What kinds of plants do you want to grow? How cold does it get at night in your area? Your heater should provide enough heat to protect the plants you want to grow from the most severe winter nights in your area.
How large of a greenhouse do you propose to heat? A kerosene heater is ordinarily best for a hobby greenhouse that is 12 feet by 12 feet or smaller.
What materials should you use in its construction? A kerosene heater requires a greenhouse that accepts light well and retains heat and humidity. Glass greenhouses are expensive to build but last longer. They retain humidity and keep heating costs to a minimum. Ninety per cent of light makes it through glass, compared to 80 per cent for double walls of plastic, although double-walled plastic can save up to 30 per cent on heat. Fibreglass walls can lose their ability to accept light over time.
Choosing a Heater
Use care when using a kerosene heater. Its radiant heat can burn nearby plants. If you want to heat a large greenhouse with kerosene, use a convection heater.
There are commercial kerosene heated marketed for small greenhouses, but you can adapt a heater used for cooking by placing a concrete block or thick steel plate on the heating rack.
High ignition temperature of the kerosene in your heater helps avoid the build-up of carbon monoxide and ethylene inside your greenhouse.
Planning Your Greenhouse
If you want to heat your greenhouse with a kerosene heater, plan the greenhouse carefully. For safety, have a flue or chimney to vent the fumes produced by burning kerosene. Ideally, place your flue or chimney against a solid end wall of the greenhouse. For good distribution of heat, install overhead ducts to carry the warm air to all parts of the greenhouse. Also use fans or reflectors to distribute heat around the greenhouse.
If possible, use a thermostat to control the temperature of your kerosene heater. Your heater also should have a feature to turn it off if there is a malfunction.