Greenhouses allow gardeners to grow plants year-round by creating an ideal microclimate inside the structure. One of the most important factors in maintaining this optimal environment is temperature control. Greenhouse heat is essential for protecting plants from cold weather and ensuring proper growth. With rising energy costs, finding the most efficient heating method is key to effective and affordable operation of a greenhouse.
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What temperature is best for a greenhouse?
The ideal greenhouse temperature range is 55-75°F during the day and 45-55°F at night. Anything below 50°F can damage plants and slow growth. Temperatures above 80°F will stress plants, especially in high humidity. Different plants have slightly different optimal temperature ranges, but most common garden and greenhouse varieties thrive in 60-70°F days and 50-60°F nights. Maintenance of these consistent warm temperatures is crucial to plant health and production.
What are the most common greenhouse heating methods?
There are several common options for heating greenhouses:
Electric heaters
Electric space heaters and electric fan-forced heaters are a popular choice. Units come in many sizes and heating capacities to accommodate small and large greenhouses. They provide instant and adjustable heat by blowing heated air around the greenhouse. Electric heaters tend to be energy inefficient, however, and can lead to high electricity bills in colder climates or extended winter use.
Gas-fired unit heaters
Propane and natural gas-fueled convection heaters are efficient and commonly used in larger greenhouses. They consist of a combustion chamber that heats up metal fins and a fan to blow the warm air into the growing space. Gas heaters provide powerful and consistent heat, but require proper ventilation. They can also be a fire hazard if not properly maintained.
Infrared radiant heaters
Infrared heaters emit electromagnetic waves that directly heat objects like plants and soil rather than warming the air. These specialized greenhouse heaters are energy efficient and ideal for targeted heating of propagation areas or heat-loving plants. Infrared heat can be limiting though in larger spaces since it does not heat the air.
Solar greenhouse heating
Passive solar heating takes advantage of sunlight to warm greenhouses. Orienting the structure to maximize southern sun exposure and using materials like thermal mass walls that absorb and slowly release heat are common solar heating design tactics. For maximum solar gain, greenhouses with sloped glazing to optimal sun angles collect more direct light and warmth. Active solar heating uses special collectors, pumped fluids, and heat exchangers to heat water or air from the sun’s energy for greenhouse warming.
Geothermal heating
Geothermal heating taps into the stable temperatures of deep underground soil. A network of underground pipes circulates water that absorbs this warmth energy. The water follows a loop to transfer its heat to the greenhouse. Though installation is complex, geothermal heating provides substantial energy savings once in place.
Wood-burning stoves
Wood stoves and electric thermostatically-controlled wood heating systems are an option for small to mid-sized greenhouses. Local wood fuel can provide inexpensive heating with a renewable resource. However, uneven heat output, fire hazards, and smoke make wood heat challenging in larger spaces.
Combined solar and supplemental heating
The most cost-effective design for a moderately cold climate is often a combination of passive solar gain paired with a supplemental heating source like propane or electric. This balanced system takes advantage of free solar warming but adds heat as needed to maintain ideal temperatures.
What factors determine the most efficient heating choice?
Choosing the optimal greenhouse heating method depends on several factors:
Climate conditions
The typical range of winter temperatures along with the duration of cold weather drives heat requirements. Cool coastal climates need less intensive heating than frigid inland mountaintops. Match heating capacity to realistic winter lows.
Size of greenhouse
The square footage being heated impacts heating choice. A propagating bench or small hobby greenhouse under 200 square feet has different options than a large commercial greenhouse. Match heating output to space requirements.
Availability of fuel types
Access to electricity, propane, natural gas, wood, or other fuel sources may determine feasible choices. Off-grid greenhouses will have different options than urban greenhouses with full utilities.
Budget for heating costs
Available funds for upfront costs and ongoing heating bills are considerations. More efficient options usually have higher initial purchase and setup costs. Compare lifetime expenses when selecting a heating system.
Ease of installation and maintenance
The complexity of heating system setup and installation matters in the decision process. Consider regular maintenance requirements as well. More maintenance needs more time and costs.
Safety issues
Preventing fire risks or fume buildup is a priority in greenhouse heating. The safety profile of the heating unit itself and proper venting need evaluation.
Crop needs
The optimal temperatures and airflow for the particular plants being grown inform heating needs. Factors like humidity control and targeted heat also play a role in plant response.
Environmental sustainability
For eco-conscious growers, the source of fuel and energy efficiency of the heating system can impact decisions. Minimizing fossil fuel use or carbon footprint may steer choices.
What is the most energy efficient greenhouse heating method?
The most energy efficient heating systems effectively warm the greenhouse while conserving resources and minimizing costs:
Passive solar gain
Optimized design for natural sunlight absorption and retention is the most efficient way to capture free heat. Proper glazing angle, insulation, thermal mass, and greenhouse orientation are key.
High-efficiency gas heaters
When solar gain alone is insufficient, high-performance gas furnaces and unit heaters offer efficient supplemental heat. Look for rated AFUE (Annual Fuel Utilization Efficiency) above 90%.
Infrared radiant heating
Infrared heaters convert over 80% of energy to heat and provide targeted, consistent warmth ideal for propagation areas and heat-loving plants.
Geothermal systems
Though expensive to install, geothermal heating can provide 4-5 times more heat energy than electrical systems from the same energy input. Efficiency ranges from 300-600%.
Sealed combustion heaters
Units that vent exhaust gases and draw combustion air separately minimize greenhouse air changes that waste warm air. Sealed combustion improves efficiency up to 15%.
High-performance glazing
Special low-e (low-emissivity) greenhouse film or rigid panels reduce radiant heat loss compared to standard glazing materials. Some coatings can minimize heat loss by over 30%.
Conclusion
The most efficient greenhouse heating system depends on climate, size, budget, and plant needs. Combining passive solar gain, high-efficiency equipment, and smart design is usually the best approach. Geothermal and infrared systems offer high-performance options for particular situations. Regardless of heating methods, the ultimate goals are maintaining optimal temperatures, minimizing costs, and maximizing plant growth and health. With a well-planned heating strategy, greenhouses can operate efficiently year-round even through cold winters.