Having an efficient and effective heating system is crucial for maintaining proper temperatures in a greenhouse, especially a small one. The heating system needs to keep plants warm enough to thrive during colder months while also being energy-efficient and reasonably priced. When selecting the best greenhouse heating system, there are several factors to consider including the size of the space, climate, budget, and types of plants being grown. The main options for heating a small greenhouse include electric heaters, propane heaters, and solar heaters.
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Key Considerations for Greenhouse Heating Systems
When evaluating heating systems for a small greenhouse, the following criteria should be taken into account:
- Greenhouse size – Systems need to be sized properly to heat the space. Underpowered units will not maintain temperatures while oversized heaters will cycle on and off and be less efficient.
- Climate and lowest expected temperatures – The heating system must keep the greenhouse warm enough for plants on the coldest days.
- Budget – Initial costs, operating costs, maintenance costs, and installation costs should fit within budget constraints.
- Types of plants – Some plants have higher or lower optimal temperature ranges. The heating system needs to provide temperatures suitable for the crops being grown.
- Supplemental heating sources – Consider combining heating systems or having a backup to ensure sufficient heating if the primary system fails.
- Energy efficiency – Look for systems with high efficiency ratings to get the most heating per unit of energy consumed.
- Safety features – Choose safe units that meet current standards and building codes.
Electric Greenhouse Heaters
Electric heaters are a common choice for heating small to medium-sized greenhouses. There are several types of electric heaters suitable for greenhouses:
Electric Fan Heaters
Fan heaters use an electric element to warm air which a fan then circulates through the greenhouse. They heat up quickly and can be wall-mounted or suspended from the ceiling. Fan heaters provide fairly uniform heating and have adjustable thermostats. On the downside, they use a lot of electricity and don’t add moisture back into the air.
Ceramic Electric Heaters
Ceramic heaters employ electric heating elements in ceramic tiles or columns. The ceramics radiate heat out into the greenhouse as they warm up. Ceramic heaters are energy efficient and good for providing zone heating in small areas. However, they provide less overall circulation compared to fan heaters.
Electric Convection Heaters
Electric convection heaters use electric coils to heat air which rises and circulates in the greenhouse due to convection. They are compact and portable but may provide uneven heating and use a lot of electricity.
Electric Radiant Heaters
Electric radiant heaters emit infrared radiation that directly warms plants and objects in the greenhouse like the sun. They provide very efficient zone heating for targeted spaces and are often installed under benches or near plants. Combining radiant heaters with a circulation fan improves temperature uniformity.
Electric Heater Pros
- Relatively affordable to purchase and install.
- Easy to control with thermostats.
- Provide quick and reliable heat.
- Multiple sizing options for small spaces.
- Zone heating possible for targeted plant areas.
Electric Heater Cons
- Can be expensive to operate continuously due to electricity usage.
- Many units require 240V power supply.
- Require electrical wiring and permits for installation in some cases.
- Dry heat requires managing greenhouse humidity.
- No ventilation options to circulate air and prevent hot spots.
Propane Greenhouse Heaters
Propane heaters are a good off-the-grid heating choice since they do not require electricity. The combustion of propane releases heat and these units can be vented or unvented. Some types of propane greenhouse heaters include:
Forced Air Propane Heaters
These propane heaters use a fan to push heated air through ducting to distribute it evenly. They provide reliable whole-space heating and humidity but require installation of ductwork.
Infrared Propane Heaters
Infrared propane heaters emit radiant heat like the sun to gently warm plants and surfaces. They provide zone heating and are often wall-mounted or suspended overhead.
Portable Propane Heaters
Small portable propane heaters on casters can supplement heating and be moved where needed. However, they present risks if not monitored closely and ventilated properly.
Propane Pros
- No electricity required so can be used off-grid.
- Fuel is relatively affordable and widely available.
- Provide drier heat than electric while adding some humidity.
- Forced air units provide whole-space heating.
- Infrared models allow targeted zone heating.
Propane Cons
- Venting and gas lines may be required for certain installations.
- Propane tanks take up space in or near the greenhouse.
- Risk of carbon monoxide is a safety concern.
- Upfront installation cost can be high for ducted systems.
- May be impractical for very small greenhouses.
Solar Greenhouse Heaters
Solar heaters harness the sun’s energy to heat water or air that is then circulated in the greenhouse. Active solar systems use pumps and controls while passive solar relies on natural conduction and convection. Solar heaters commonly used in greenhouses include:
Solar Air Collectors
These systems use glazed boxes to trap solar radiation and heat air passing through them. Fans or convection move the warmed air into the greenhouse interior space.
Solar Hydronic Heating
Solar hydronic systems use solar collectors to heat water or other fluid that is pumped through pipes in the greenhouse to release heat.
Passive Solar Design
Passive solar greenhouses are designed to optimize solar heat retention naturally through glazing materials, insulation, thermal mass, and ventilation.
Solar Heater Pros
- Provide free heat from the sun’s radiation.
- Can significantly offset traditional heating costs.
- Renewable energy source with very low emissions.
- Work well alongside other heat sources as a supplement.
- Can be DIY or professionally installed.
Solar Heater Cons
- Daytime solar heat requires thermal mass to retain warmth at night.
- Do not work well as a standalone system in cold or cloudy conditions.
- Require glazing that compromises insulating at night.
- Active systems require pumps, controls and electrical power.
- Higher upfront costs than traditional heaters.
Comparing Heating System Options
Here is a comparison of some key factors to consider when choosing a greenhouse heating system:
| Heater Type | Upfront Cost | Operating Cost | Installation Requirements | Heat Distribution | Humidity |
|---|---|---|---|---|---|
| Electric Fan Heater | Low | High electricity usage | Electrical hookup | Fairly uniform | Dry heat |
| Ceramic Electric | Low | Moderate electricity usage | Electrical hookup | Zone heating | Dry heat |
| Forced Air Propane | High | Moderate fuel cost | Venting, gas line | Very uniform | Adds humidity |
| Infrared Propane | Moderate | Moderate fuel cost | Venting, gas line | Zone heating | Adds humidity |
| Active Solar | High | Low ongoing costs | Collectors, controls | Fairly uniform | Dry heat |
| Passive Solar | Low | Very low costs | Solar design | Somewhat uneven | Dry heat |
When comparing heating systems, it is important to consider both the upfront costs of equipment and installation as well as the ongoing costs for operation based on fuel type and electricity usage. The distribution of heat, impacts on humidity, and installation requirements also inform the decision making process. Using this criteria to evaluate options allows growers to select the optimal heating solution for their specific greenhouse.
Conclusion
Determining the best greenhouse heating system involves assessing the size of the space, intended use, climate conditions, budget, and plants being grown. For a small greenhouse, electric heaters provide an affordable and easy heating option. Fan heaters distribute warmth evenly while ceramic heaters efficiently heat zones. Propane heaters are a good off-grid choice since they do not require electricity. Forced air propane systems heat well, while infrared models provide targeted radiant heating. Solar heaters can offset a significant portion of heating costs by harnessing free solar energy, especially in sunny climates. Passive solar greenhouses incorporate design elements for naturally retaining heat. There is no definitive heating system that is ideal for every scenario. By carefully weighing the costs, installation requirements, heat distribution, and other factors, growers can select the right heating solution to cost-effectively keep their small greenhouse warm.