The ideal greenhouse heater will distribute heat efficiently and evenly throughout and will have an automatic thermostat and an automatic turn-off feature for safety.
An adjustable thermostat with an anti-frost setting will protect your plants from frostbite by turning itself on when the temperature dips hazardously while you're sleeping. An automatic shutdown feature will turn the heater completely off if it is tipped or overheated.
Gas heaters emit carbon dioxide and water, so you will want to carefully consider this and whether such a unit is appropriate for your greenhouse. There are vented and non-vented models, and some building code regulations will prohibit the use of non-vented heaters in greenhouses. You'll want to ensure proper ventilation in any case!
Heat distribution is achieved with a built-in fan or a heat-reflection feature. To determine the BTU (British Thermal Unit) requirement for your greenhouse, you will take into account the exterior square footage, the lowest possible temperatures in your area, the lowest temperature your plants can comfortably tolerate, and the building material used in the construction of your greenhouse. Most greenhouse manufacturers and greenhouse heater suppliers will help you with this calculation.
An electrical heater with the ideal features and producing 5600 BTUs will cost about $100, while a gas-burning unit producing up to 20,000 BTUs will cost about $450.
To learn more about the variety of greenhouse heaters on the market today, check out the shopping links at the top of this page.