A greenhouse heater can protect seedlings, extend the growing season and make valuable plants less vulnerable to sudden cold. The best choice depends on more than the unit’s purchase price. Climate, greenhouse size, insulation, available power and the crops being grown all influence the real cost of keeping temperatures stable.
Australian gardeners face very different conditions across the country. A hobby greenhouse in Hobart or the Dandenong Ranges may need frost protection through winter, while a structure in Darwin may rarely need heating at all. In Sydney, Melbourne and Adelaide, cool nights can still affect tomatoes, citrus seedlings and tropical plants, particularly during early spring.
Angelo Bernacchi Greenhouse has supplied greenhouse products and services since 1906, with an emphasis on practical advice and customer service. That long retail and wholesale perspective is useful when comparing heating systems, because a reliable setup should suit both the plants and the person paying the energy bills.
Before comparing heaters, estimate how quickly the structure loses warmth. A small polycarbonate greenhouse with sealed doors may require modest supplementary heat, whereas an older glass house with gaps around the frame can lose heat rapidly after sunset. Bubble insulation, thermal screens, draft sealing and a solid base often reduce running costs more effectively than upgrading to a larger heater.
Measure the internal length, width and height, then consider the coldest local conditions rather than the average winter temperature. Canberra and inland New South Wales can experience sharp overnight frosts, while Melbourne’s damp winter weather creates a different heating challenge. In northern Queensland, ventilation and shade may matter more than heating for most of the year.
A thermostat is essential for budget control. It switches the heater on only when the temperature drops below a selected level, avoiding the waste of running continuously. A minimum temperature of 5–8°C may protect many dormant plants, while warm-season crops could require 12–18°C. Check each plant’s needs rather than heating the entire greenhouse to the highest requirement.
Electric fan heaters are usually the simplest choice for a small backyard greenhouse. They are easy to install, widely available in Australia and capable of distributing warmth quickly. Look for a model with a thermostat, overheat protection and an appropriate ingress-protection rating. Electricity can become expensive if the heater runs overnight, so calculate wattage multiplied by operating hours before buying.
A tube heater or oil-filled electric radiator provides gentler, quieter warmth and may suit propagation benches or compact spaces. Fanless models reduce air movement, which can be helpful for delicate seedlings, although they may distribute heat less evenly. Ceramic heating elements can offer fast warm-up, but their purchase price should be compared with expected running time.
Gas heaters can be useful in large commercial or semi-commercial structures where electrical supply is limited. LPG and natural gas systems require careful ventilation because combustion consumes oxygen and can produce carbon monoxide and excess moisture. Installation and connection should be handled by appropriately licensed tradespeople. Australian state and territory rules differ, and gas appliances must comply with relevant safety requirements.
Passive solar heating costs less to operate but cannot replace a dependable heater during severe cold. Water barrels, stone paths and thermal mass absorb warmth during sunny days and release it slowly overnight. They work best when paired with insulation and a thermostatically controlled backup unit. In a sunny Perth or Adelaide location, this combination may provide good value for a seasonal hobby greenhouse.
With a limited budget, prioritise a safe electric heater and a separate digital thermostat if the built-in control is unreliable. Seal obvious gaps, raise pots off a cold floor and use horticultural fleece around particularly sensitive plants. Spending a little on insulation can reduce the size and runtime of the heater required.
A mid-range setup might combine a thermostatic tube heater, insulated walls and a small circulation fan. Air circulation prevents cold pockets and reduces condensation on leaves, but the fan should not blast directly at young plants. Place the temperature sensor near plant height, away from the heating element, doors and direct sunlight.
For a larger budget, zoned heating can be more efficient than warming unused floor space. Heated propagation benches, root-zone cables and separate thermostats allow seedlings to receive warmth while established plants remain cooler. This approach is especially valuable for growers supplying local markets, where consistent crop quality can justify higher equipment costs.
Second-hand equipment can lower the initial price, but age and condition matter. Inspect plugs, cables, thermostats, guards and signs of corrosion before purchase; advice on how to inspect second-hand finds is relevant because a refurbished-looking object may contain mismatched or unsafe components. Never use a heater with damaged wiring or unknown internal repairs in a damp greenhouse.
A heater’s label shows its power draw in watts. Divide watts by 1,000 to find kilowatts, then multiply by hours of operation and the electricity tariff. For example, a 1,500-watt heater running for six hours uses 9 kWh. The final cost depends on the household plan, controlled-load arrangements and seasonal rates, so check a recent Australian electricity bill rather than relying on a generic estimate.
Solar panels can make daytime heating more affordable, but most greenhouse heating is needed after sunset, when solar generation has stopped. Batteries may help but add substantial capital cost. Time-of-use tariffs can also change the calculation, especially in larger homes or nurseries. A lower thermostat setting, thermal curtain and weatherproof seals often provide a faster payback than adding sophisticated controls.
Fuel costs should include delivery, cylinder hire, servicing and ventilation work. LPG may appear economical for a large space, but frequent cylinder replacement can erase the saving. Combustion heaters also add moisture, which can encourage fungal disease if air exchange is poor. Monitor humidity with a hygrometer and open vents when conditions allow, even during cooler weather.
For businesses, keep records of overnight temperatures, energy use and crop losses. Those figures make it easier to decide whether a premium heating system is worthwhile. A small increase in survival rates can matter to a wholesale grower, while a home gardener may prefer a basic unit that protects a modest collection without creating a large monthly bill.
Place the heater on a stable, non-combustible surface with clear space around air inlets and outlets. Keep plastic film, potting mix, cardboard and dry plant material away from hot surfaces. Use an outdoor-rated extension solution only where permitted, and protect electrical connections from watering, condensation and puddles. In Australia, electrical installation and fixed wiring should be completed by a licensed electrician.
A residual-current device, or safety switch, adds protection in damp environments, but it does not make damaged equipment safe. Test the switch according to manufacturer instructions and inspect cables at the start of each season. Never use an indoor portable heater in a wet greenhouse unless its specifications clearly allow that environment.
Automation improves consistency. A thermostat can control the heater, while a separate sensor or smart monitor records temperature and humidity. Set an alert for unusually low readings, especially when frost threatens in Tasmania or the Victorian high country. Backup measures such as frost cloth, water containers and a charged torch are sensible during power interruptions.
Finally, select heating capacity around the plants you actually grow. Resources such as greenhouse growing ideas can help identify seasonal crops and inform temperature targets. The most economical greenhouse heater is rarely the cheapest unit on the shelf; it is the safe, correctly sized system that protects the crop while using heat only when the plants need it.