Installing an efficient and reliable greenhouse heating system is one of the most critical investments for controlled environment plant growth. The right greenhouse heating system allows maintaining ideal temperatures in your greenhouse, even through frigid weather and cold seasons. This climate control maximizes plant health and productivity year-round.

However, with the variety of greenhouse heating systems available, selecting the right technology for your specific needs requires comparing factors like:

• Installation and equipment costs
• Operating and maintenance expenses
• Heating efficiency and control
• Environmental sustainability
• Ease of management

This guide compares five common greenhouse heating system options:

• Solar Thermal Greenhouse Heating Systems
• Geothermal Greenhouse Heating Systems
• Natural Gas Greenhouse Heating Systems
• Biomass Greenhouse Heating Systems
• Compost Greenhouse Heating Systems

We’ll analyze the costs, efficiency, pros and cons of each to help you choose the best greenhouse heating system for your operation.

Key Selection Factors for a Greenhouse Heating System

Before exploring the specific technologies, here are some important criteria to evaluate when selecting a greenhouse heating system:

Greenhouse Size and Layout

Greenhouse heating systems range from small DIY kits to large commercial scale boilers and furnaces. New build greenhouses can customize around your system, while existing builds may require retrofitting.

Climate and Supplemental Heat Needed

Cooler northern regions need more heavy-duty heating than milder southern climates. Your climate also impacts fuel availability.

Installation and Equipment Costs

Upfront investment for the heating unit and installation ranges widely. But operating costs accumulate over years of use.

Efficiency and Temperature Control

Look for systems that reliably maintain steady temperatures, especially overnight during cold periods.

Fuel Source and Environmental Factors

Fossil fuels produce emissions, while renewable sources offer sustainability benefits.

With these selection criteria in mind, let’s compare popular greenhouse heating system options.

Solar Thermal Greenhouse Heating Systems

Solar thermal greenhouse heating harnesses free sunlight and converts it into usable heat. Passive solar uses greenhouse design to capture sunlight. Active solar adds collectors and heating distribution components.

Passive Solar Heating

Passive solar utilizes the greenhouse structure itself as a solar collector. Design factors like glazing material, insulation, thermal mass, and ventilation trap and release heat from the sun shining through.

For example, materials with thermal mass like concrete floors or water barrels absorb and slowly emit heat. Vents release excess warm air to prevent overheating.

Active Solar Heating

Active solar thermal systems use solar collectors to absorb heat from sunlight. The thermal energy transfers into the greenhouse space via pumps or fans. Common collector types include:

• Flat plate collectors – thin insulated boxes containing dark absorber plates to heat liquid or air.
• Evacuated tube collectors – glass tubes containing fluid that’s heated and circulated.
• Unglazed perforated metal plates that heat air moving by convection.

Pros of Active Solar Greenhouse Heating:

• Renewable, low operating costs after installation
• Reduces fossil fuel usage and emissions
• Evacuated tube collectors offer high efficiency
• Can integrate with passive solar design

Cons of Active Solar Greenhouse Heating:

• High initial investment in solar collectors
• Limited cold weather output with fewer sunny days
• Solar heat output varies through seasons

Ideal Conditions for Solar Greenhouse Heating:

• Greenhouses in regions with winter sunlight
• Small-midsize greenhouses with lower heating loads
• Combining with passive solar or backup heating system

Solar Greenhouse Heating Costs:

• Passive solar glazing/materials – $3 – $8 per sq. ft installed
• Unglazed air collectors – $50 – $70 per sq. ft
• Flat plate collectors – $400 – $800 per panel
• Evacuated tube collectors – $1800 – $3000 per 20-tube panel

Geothermal Greenhouse Heating Systems

Geothermal greenhouse heating uses subsurface Earth temperatures for heating and cooling via a ground source heat pump (GSHP). Below ground pipes circulate liquid through the Earth, absorbing or depositing heat.

In winter, the system takes warmth from the ground and conveys it into the greenhouse through a heat exchanger. The process reverses in summer, pulling heat from the greenhouse and releasing it into the cooler ground.

Pipes are installed vertically in 150-300 foot boreholes or horizontally in trenches around 4 feet deep laid in large looping grids. Vertical is more efficient but requires well drilling equipment. Horizontal trenching needs more yard space for piping loops.

Pros of Geothermal Greenhouse Heating:

• Extremely energy efficient heating and cooling
• Provides consistent year-round temperature regulation
• Small electric pump is the only energy input needed
• Long lifespan system with low maintenance

Cons of Geothermal Greenhouse Heating:

• Substantial upfront investment for ground loops
• Requires large property space for loops
• Challenging retrofitting existing greenhouses

Ideal Conditions for Geothermal Heating:

• New build greenhouses allow designing around loops
• Adequate land space for horizontal loops or bore wells
• Large operations with high heating/cooling loads

Geothermal Greenhouse Heating Costs:

• Vertical loops – $15,000 – $25,000 installed
• Horizontal loops – $5,500 – $8,000 installed
• Heat pump unit – $4,500 – $10,000
• Total System Cost – $10,000 – $35,000+

Natural Gas Greenhouse Heating Systems

Natural gas is a common greenhouse heating fuel. Direct-fired heaters provide forced hot air. Radiant heat tube systems emit infrared waves for plants to absorb.

Direct-fired units utilize a gas burner to produce hot air distributed through greenhouse ductwork. Radiant heat systems circulate heated gases through overhead tubes that release warmth that plants below take in via infrared radiation.

Natural gas systems allow precise temperature control. Combining direct-fired convection heating with radiant heat maintains optimal daytime and nighttime conditions. Gas is sourced from existing utility lines and requires venting emissions safely outside.

Pros of Natural Gas Greenhouse Heating:

• Lower equipment cost than many heating systems
• Easy to install and connect to existing gas lines
• Delivers precise temperature control through thermostats
• Reliable and consistent fuel source in many regions

Cons of Natural Gas Heating:

• Emits greenhouse gases through gas combustion
• Potential for temperature fluctuations if undersized
• Requires professionals for gas line maintenance
• Rising utility costs can increase long-term expenses

Ideal Conditions for Natural Gas Heating:

• Existing onsite natural gas supply lines
• Ability to safely vent emissions outside
• Large commercial scale operations

Natural Gas Greenhouse Heating Costs:

• Direct-fired heaters – $1.50 – $5 per sq. ft installed
• Radiant tube heaters – $2 – $6 per linear ft installed
• Total system cost – $15,000 – $100,000+

Biomass Greenhouse Heating Systems

Biomass systems burn renewable organic materials like wood, agricultural residues, and biofuel crops to heat greenhouses. A furnace or stove feeds a distribution system.

Wood chips, pellets, nut shells, and crop waste can provide agricultural biomass fuels. Cultivating dedicated biofuel crops works for large operations. Automatic pellet feeders provide convenience.

Pros of Biomass Greenhouse Heating:

• Uses agricultural residues and waste as renewable fuel
• Potentially carbon neutral fuel source
• Fuel can be sustainably produced onsite or locally sourced
• Lower heating expenses compared to fossil fuels

Cons of Biomass Heating:

• High labor needs for fuel processing and loading
• Combustion particles may require greenhouse cleaning
• Requires fuel storage and ash removal systems
• More mechanical maintenance than some systems

Ideal Conditions for Biomass Heating:

• Sufficient local biomass fuel supply and processing
• New greenhouses designed for biomass systems
• Adding heat storage tanks for off-peak heating

Biomass Greenhouse Heating Costs:

• Wood pellet stove system – $3,000 – $8,000 installed
• Wood chip/multi-fuel boiler – $15,000 – $80,000+ installed
• Additional costs for fuel supply and storage

Compost Greenhouse Heating Systems

Composting organic waste produces some excess heat. Compost greenhouse heating systems try to capture and redirect a small portion of this heat into the greenhouse but have very limited capacity.

Piping buried in active compost piles collects minor heat that transfers into the greenhouse through fans or pumps. Odor and condensation are potential issues needing mitigation.

Pros of Compost Greenhouse Heating:

• Makes use of heat from onsite composting
• Very inexpensive to construct and operate
• Extends composting season by retaining some warmth

Cons of Compost Greenhouse Heating:

• Extremely minimal heating capacity – not standalone
• Requires large compost piles for meaningful heat
• Odor and condensation control required

Ideal Conditions for Compost Heating:

• Hobbyist greenhouses with minimal supplemental heat needs
• Adding to other heat systems like solar or wood pellets
• Containing and insulating piles

Compost Greenhouse Heating Costs:

• Simple batch system – $500 – $2000 in materials
• Larger managed static pile – $5000 – $15,000+
• Very low operating expenses

Conclusion – Selecting the Best Greenhouse Heating System

Choosing the right greenhouse heating system depends on balancing factors like:

• Available fuels and resources in your region
• Initial costs against long-term operating expenses
• Your greenhouse size and layout
• Precise temperature control needed
• Environmental sustainability preferences

For small hobby greenhouses, combining solar collectors with biofuel stoves or compost heating provides eco-friendly solutions. Larger operations often install efficient radiant and forced air natural gas or geothermal systems.

Carefully weigh installation costs against lifetime operating costs and efficiency. There is no universally superior greenhouse heating system. The optimal solution depends on your specific conditions and needs. A tailored approach utilizing multiple technologies can provide the ideal temperatures for your greenhouse to thrive in any weather.

Frequently Asked Questions About Greenhouse Heating Systems

What is the best greenhouse heating system?

There is no universally “best” system. The optimal system depends on your climate, greenhouse size, budget, and needs. Often a combination of technologies like solar and gas work together provides the ideal solution.

What size greenhouse heater do I need?

Size your heater based on factors like your greenhouse square footage, insulation level, and climate conditions. For hobby greenhouses under 300 sq ft, a portable space heater may suffice. Larger operations need powerful furnaces or boilers.

How much does it cost to heat a greenhouse?

Heating costs vary widely based on system type, fuel prices, and climate. Geothermal and solar have higher startup costs but lower operating expenses. Gas and biomass have lower initial costs but higher ongoing fuel costs.

What is the most energy efficient greenhouse heating?

Geothermal heat pumps are the most efficient, leveraging underground temperatures. Well-insulated passive solar greenhouse design also provides high efficiency supplemental heating.

Can you use a wood stove to heat a greenhouse?

Yes, wood stoves can provide economical radiant and convection greenhouse heating. However, they require frequent maintenance and labor to load fuel compared to automated biomass systems.

What temperature should a greenhouse maintain in winter?

Ideal greenhouse temperatures typically range from 55°F to 75°F in winter depending on the crops grown. Cool weather plants need lower minimum temps while heat-loving plants require warmer conditions.

How is a radiant heat greenhouse heated?

Radiant heat systems use emitter tubes to heat and circulate gases, generating infrared radiation that plants below absorb. This provides very even, consistent zone heating without temperature swings.

What are the disadvantages of geothermal heating?

Upfront costs for digging ground loops are high. Geothermal also requires substantial land space for horizontal loops or drilling vertical wells. Retrofitting existing greenhouses can be challenging.

Does passive solar greenhouse design work?

Yes, optimized passive solar design provides worthwhile heat in milder climates. Thermal mass, insulation, glazing materials, and ventilation traps solar warmth effectively as supplemental heating.

Which biomass fuels can heat greenhouses?

Wood pellets, chips, agricultural residues like nut shells or straw, and biofuel crops like Miscanthus grasses can provide renewable biomass fuels to heat greenhouses.