How to Heat a Small Greenhouse Cheaply in Winter

Last Updated on October 19, 2026 by D. Ruddy

Heating a small greenhouse cheaply in winter doesn’t have to break the bank. With the right strategies, you can keep your plants warm and healthy without spending a fortune on energy bills. This guide covers practical, budget-friendly methods to maintain the ideal temperature for your greenhouse all season long.

Simply put, heating a small greenhouse cheaply in winter involves using passive solar energy, insulation, and low-cost heating solutions like compost, thermal mass, or small heaters. These methods can keep your greenhouse 10-20°F warmer than outdoor temperatures with minimal cost.

Key Takeaways

• Heating a small greenhouse cheaply in winter is achievable with DIY solutions and smart design choices.
• Passive solar heating and proper insulation can reduce the need for expensive heaters.
• Thermal mass materials like water barrels or bricks absorb heat during the day and release it at night.
• Compost, manure, or small electric heaters are cost-effective ways to generate warmth.
• Sealing gaps and using bubble wrap or thermal curtains can prevent heat loss.

What Is Passive Solar Heating and How Does It Work?

Passive solar heating is the most cost-effective way to heat a small greenhouse cheaply in winter. It relies on the sun’s natural energy to warm the space without electricity or fuel. The greenhouse structure itself acts as a solar collector, trapping heat during the day and slowly releasing it at night.

To maximize passive solar heating, position your greenhouse to face south (in the Northern Hemisphere) or north (in the Southern Hemisphere). This ensures it receives the most direct sunlight throughout the day. Use materials like double-walled polycarbonate panels or insulated glass to improve heat retention.

• Orientation: South-facing (or north-facing in the Southern Hemisphere) for maximum sunlight exposure.
• Materials: Double-walled polycarbonate, insulated glass, or thick plastic sheeting to trap heat.
• Glazing: Clean and transparent to allow maximum light penetration.
• Ventilation: Proper vents to release excess heat during the day and prevent overheating.
• Shading: Use shade cloths in summer to avoid overheating but remove them in winter.

Tip: Paint the north wall of your greenhouse black or use dark-colored thermal mass to absorb more heat during the day.

How to Use Thermal Mass to Store and Release Heat

Thermal mass refers to materials that absorb heat during the day and slowly release it at night, helping to stabilize temperatures. This is one of the most effective ways to heat a small greenhouse cheaply in winter without ongoing costs. Common thermal mass materials include water, bricks, concrete, and stone.

Water is particularly effective because it has a high heat capacity, meaning it can store a lot of energy relative to its volume. Place black-painted water barrels or jugs along the north wall or in the center of the greenhouse. During the day, they’ll absorb heat, and at night, they’ll radiate warmth back into the space.

For best results, combine multiple thermal mass materials. For example, use water barrels for their high heat capacity and bricks for their ability to radiate heat quickly.

How to Insulate a Greenhouse for Maximum Heat Retention

Proper insulation is key to heating a small greenhouse cheaply in winter. Without insulation, heat escapes quickly, forcing you to rely on expensive heating methods. The goal is to minimize heat loss through walls, floors, and gaps while still allowing sunlight to enter.

Start by sealing any gaps or cracks in the greenhouse frame, doors, or vents. Use weatherstripping or caulk to close these openings. For additional insulation, consider the following methods:

1. Bubble wrap insulation: Apply a layer of bubble wrap to the interior of the greenhouse glazing. It allows light to pass through while reducing heat loss by up to 50%. Secure it with clips or tape, and replace it if it becomes damaged.
2. Thermal curtains or blankets: Use insulated curtains or blankets to cover the glazing at night. These can be made from old blankets, bubble wrap, or specialized greenhouse insulation fabric. Open them during the day to let sunlight in.
3. Double-glazing: If your greenhouse has single-layer glazing, add a second layer with a small air gap in between. This creates a buffer zone that reduces heat transfer.
4. Floor insulation: Insulate the floor with straw, wood chips, or foam boards. This prevents heat from escaping into the ground, which can account for 10-20% of heat loss.
5. Wall insulation: For permanent greenhouses, add insulation panels to the north wall or other non-glazed surfaces. Use materials like foam board, fiberglass, or reflective insulation.

Warning: Avoid blocking vents completely, as proper ventilation is still needed to prevent humidity buildup and plant diseases.

How to Use Compost or Manure for Natural Heat

Compost and manure generate heat as they decompose, making them an excellent, low-cost way to heat a small greenhouse cheaply in winter. This method, known as a “hot bed,” has been used for centuries to provide bottom heat for plants. The heat comes from microbial activity, which can raise temperatures by 20-50°F above the surrounding air.

To create a hot bed, dig a pit or trench in the center of your greenhouse (about 1-2 feet deep) and fill it with fresh manure or compost. Cover it with a layer of soil or straw to contain the heat. For best results, use horse, cow, or chicken manure, as these generate the most heat.

Turn the compost regularly to maintain microbial activity.

• Materials needed: Fresh manure (horse, cow, or chicken), compost, straw or soil for covering.
• Location: Center of the greenhouse or along the north wall for even heat distribution.
• Depth: 1-2 feet deep for optimal heat generation.
• Maintenance: Turn the compost every 1-2 weeks to keep it active.
• Safety: Avoid using manure from carnivorous animals (e.g., cats, dogs) as it may contain harmful pathogens.
• Duration: A well-maintained hot bed can provide heat for 4-8 weeks.

Compost heat is especially effective for starting seeds or rooting cuttings, as it provides gentle, consistent warmth from below.

What Are the Best Low-Cost Heaters for a Small Greenhouse?

If passive methods aren’t enough, you can supplement with low-cost heaters to heat a small greenhouse cheaply in winter. The key is to choose energy-efficient models that provide enough warmth without driving up electricity bills. Here are some of the best options:

1. Electric Fan Heaters

Electric fan heaters are affordable and effective for small greenhouses. They’re easy to install and provide instant heat. Look for models with thermostats to maintain a consistent temperature and avoid wasting energy.

• Pros: Affordable, easy to install, instant heat, portable.
• Cons: Can be energy-intensive if used continuously, may dry out the air.
• Best for: Small greenhouses (under 100 sq ft) with access to electricity.
• Cost: $20-$50 for basic models, $50-$100 for thermostat-controlled units.

2. Radiant Heaters

Radiant heaters warm objects directly rather than the air, making them more efficient for greenhouses. They’re ideal for spot heating and can be mounted on walls or ceilings. Infrared heaters are a type of radiant heater that’s particularly energy-efficient.

• Pros: Energy-efficient, heats plants directly, silent operation.
• Cons: More expensive upfront, may not heat the entire greenhouse evenly.
• Best for: Medium-sized greenhouses (100-200 sq ft) with tall plants.
• Cost: $50-$150.

3. Propane Heaters

Propane heaters are a good option if you don’t have access to electricity. They’re portable and can provide a lot of heat for their size. However, they require proper ventilation to avoid carbon monoxide buildup.

• Pros: No electricity needed, portable, high heat output.
• Cons: Requires ventilation, fuel costs can add up, emits CO2.
• Best for: Remote greenhouses without electricity.
• Cost: $50-$150 for the heater, plus propane tank costs.

For most small greenhouses, an electric fan heater with a thermostat is the best balance of cost and efficiency. If you’re heating a larger space, consider a radiant heater or a combination of methods.

How to Prevent Heat Loss in a Greenhouse at Night

Nighttime heat loss is one of the biggest challenges when trying to heat a small greenhouse cheaply in winter. Without the sun’s warmth, temperatures can plummet quickly. To combat this, use a combination of insulation, thermal mass, and heat retention strategies.

Start by covering your greenhouse glazing with thermal curtains or blankets at dusk. This creates an additional barrier against the cold. You can also use a layer of bubble wrap on the interior of the glazing, which traps air and reduces heat transfer.

1. Seal all gaps: Check for drafts around doors, vents, and the foundation. Use weatherstripping, caulk, or foam tape to seal any openings.
2. Use double glazing: If your greenhouse has single-layer glazing, add a second layer with an air gap for better insulation.
3. Add a ground cover: Cover the soil with straw, mulch, or landscape fabric to prevent heat from escaping into the ground.
4. Install a heat sink: Place thermal mass materials like water barrels or bricks in the greenhouse to absorb and release heat.
5. Use a greenhouse heater: If temperatures drop too low, use a small electric or propane heater with a thermostat to maintain a consistent temperature.
6. Ventilate during the day: Open vents or doors during sunny days to prevent overheating and allow fresh air to circulate.
7. Monitor temperature: Use a greenhouse thermometer to track temperature changes and adjust your heating methods accordingly.

Important: Avoid using plastic sheeting as a long-term insulation solution, as it can degrade quickly and reduce light penetration.

What Are Common Mistakes to Avoid When Heating a Greenhouse?

Even with the best intentions, it’s easy to make mistakes that can undermine your efforts to heat a small greenhouse cheaply in winter. Here are some common pitfalls and how to avoid them:

• Overheating during the day: While it’s important to retain heat at night, overheating during the day can be just as harmful. Always ventilate your greenhouse during sunny days to prevent temperatures from rising too high, which can damage plants or cause excessive humidity.
• Ignoring insulation: Many people focus on heating sources but neglect insulation. Without proper insulation, heat escapes quickly, making your heating efforts less effective and more expensive.
• Using inefficient heaters: Some heaters, like space heaters designed for indoor use, are not energy-efficient for greenhouses. Choose heaters specifically designed for greenhouse use or those with thermostats to control energy usage.
• Poor placement of thermal mass: Thermal mass materials like water barrels should be placed where they can absorb the most sunlight during the day. Avoid placing them in shaded areas or where they won’t receive direct light.
• Neglecting ventilation: Sealing your greenhouse too tightly can lead to humidity buildup, which encourages mold, mildew, and plant diseases. Always allow for some airflow, even in winter.
• Not monitoring temperature: Temperature fluctuations can stress plants. Use a thermometer to monitor the greenhouse environment and adjust your heating methods as needed.
• Using unsafe heating methods: Avoid using open flames, unvented propane heaters, or DIY heaters that could pose a fire or carbon monoxide risk. Always prioritize safety.

How to Calculate the Heating Needs of Your Greenhouse

To heat a small greenhouse cheaply in winter, it’s important to understand its heating requirements. This depends on factors like size, insulation, glazing material, and the temperature difference between inside and outside. Here’s a simple way to estimate your heating needs:

Greenhouses lose heat through their surfaces, including walls, roof, and floor. The rate of heat loss is measured in BTUs (British Thermal Units) per hour. To calculate this, you’ll need to know:

• The surface area of your greenhouse (in square feet).
• The U-value of your glazing material (a measure of heat transfer; lower U-values mean better insulation).
• The temperature difference between inside and outside (in °F).

Use this formula to estimate heat loss:

Heat Loss (BTU/hour) = Surface Area (sq ft) × U-value × Temperature Difference (°F)

For example, a 10 ft × 12 ft greenhouse (120 sq ft surface area) with double polycarbonate glazing (U-value = 0.35) and a 30°F temperature difference would lose:

120 sq ft × 0.35 × 30°F = 1,260 BTUs/hour

To maintain this temperature, you’d need a heater capable of producing at least 1,260 BTUs/hour. For larger greenhouses or colder climates, you’ll need a higher capacity heater.

Tip: Use an online greenhouse heat loss calculator to get a more precise estimate based on your specific greenhouse dimensions and materials.

Frequently Asked Questions

Can I use a space heater to heat my greenhouse?

Yes, you can use a space heater, but it’s important to choose one designed for greenhouse use or with safety features like a thermostat and tip-over protection. Avoid using indoor space heaters, as they may not be weatherproof or safe for greenhouse environments. Electric fan heaters or radiant heaters are better options.

How warm should my greenhouse be in winter?

The ideal temperature depends on the plants you’re growing. Most cool-season crops (like leafy greens, spinach, and kale) thrive in temperatures between 45-65°F (7-18°C). Warm-season crops (like tomatoes, peppers, and cucumbers) need temperatures between 60-85°F (15-29°C).

Use a thermometer to monitor and adjust as needed.

Is it safe to use a propane heater in a greenhouse?

Propane heaters can be used in greenhouses, but they require proper ventilation to prevent carbon monoxide buildup. Never use unvented propane heaters in an enclosed space. If you choose a propane heater, opt for a model designed for greenhouses or outdoor use, and ensure there’s adequate airflow.

How can I heat my greenhouse without electricity?

There are several ways to heat a greenhouse without electricity, including passive solar heating, thermal mass (water barrels, bricks), compost or manure heat, and propane heaters. Combining these methods can provide consistent warmth without relying on electrical power.

What’s the cheapest way to heat a greenhouse?

The cheapest way to heat a greenhouse is to use passive solar heating combined with thermal mass and insulation. These methods require little to no ongoing costs and can keep your greenhouse warm by harnessing natural energy. Adding a layer of bubble wrap or thermal curtains can further reduce heat loss without spending much money.

Final Thoughts

Heating a small greenhouse cheaply in winter is all about combining smart design, passive heating methods, and cost-effective solutions. By maximizing solar gain, using thermal mass, insulating properly, and supplementing with low-cost heaters when needed, you can keep your greenhouse warm without breaking the bank.

Remember to monitor temperatures regularly and adjust your heating strategies as the season progresses. With the right approach, you can enjoy a thriving greenhouse garden year-round, even in the coldest months.