Choosing the best heater for a small greenhouse involves balancing heat output, energy efficiency, and safety features for your plants. This guide will help you navigate the options to find the perfect heating solution for your compact growing space.
Getting it right means your plants thrive through cold snaps. Getting it wrong can lead to lost crops and higher bills. Let’s break down everything you need to know.
Best Heater For Small Greenhouse
Finding the Best Heater For Small Greenhouse is not a one-size-fits-all task. The ideal model depends on your specific structure, climate, and what you’re growing. We will examine the top types and specific models that perform well in small environments.
Small greenhouses, typically those under 100 square feet, have unique needs. They can lose heat quickly but also overheat fast if the heater is too powerful. Your goal is consistent, gentle warmth.
Key Factors To Consider Before You Buy
Before looking at specific heaters, assess your greenhouse’s requirements. This will narrow your search instantly.
Greenhouse Size and Insulation
First, calculate your greenhouse’s cubic footage (length x width x height). Heater capacity is measured in BTUs, and you’ll need roughly 20-30 BTUs per cubic foot for a moderately insulated structure. A well-insulated greenhouse with double-walled polycarbonate or bubble wrap will need less.
Your Local Climate
Are you facing mild winters or deep freezes? The lowest expected temperature dictates the heater’s power. A zone 7 gardener has different needs than someone in zone 4.
Power Source Availability
This is a major deciding factor. What do you have access to?
- Electricity: The most common and convenient for small setups.
- Propane: Good for off-grid situations but requires ventilation.
- Natural Gas: Efficient for permanent setups, needs professional installation.
Safety Features
This is non-negotiable. Look for:
- Tip-over automatic shutoff.
- Overheat protection.
- Cool-touch exteriors (especially for plastic greenhouses).
- UL or ETL certification for electric models.
Types Of Heaters For Small Greenhouses
Each heater type has its pros and cons. Understanding these will guide your choice.
Electric Fan Heaters
These are popular for their affordability and immediate heat distribution. The fan circulates warm air, preventing cold spots. They are best for greenhouses with good electrical access and where humidity isn’t extreme.
- Pros: Inexpensive, portable, quick heat, often include thermostats.
- Cons: Can dry air, fan noise, relies on electricity.
Electric Radiant Heaters
Radiant heaters warm objects and plants directly, like sunshine, rather than heating the air. They are quite efficient for spot heating and work well for benches or specific plant zones.
- Pros: Silent operation, direct heat, good for targeted areas.
- Cons: Less effective for whole-space heating, can create uneven temps.
Propane Heaters
Propane heaters are powerful and portable, making them a classic choice for off-grid heating. Ventilation is critical to remove moisture and combustion byproducts like ethylene, which can harm plants.
- Pros: High heat output, no electricity needed, portable.
- Cons: Requires ventilation, adds humidity, needs fuel monitoring.
Oil-Filled Radiator Heaters
These heaters use electricity to heat sealed oil, which then radiates warmth. They provide a steady, gentle heat with no fan. They are very safe and good for maintaining a baseline temperature.
- Pros: Silent, safe, consistent heat, no dry air.
- Cons: Slower to warm up, heavier, less portable.
Top Heater Recommendations And Reviews
Based on the criteria above, here are some highly-regarded heaters for small greenhouses.
Best Overall Electric: Dr Infrared Heater Portable Space Heater
This model combines a ceramic heating element with a quiet fan and optional radiant heat. Its dual heating system provides fast and consistent warmth. It includes a thermostat, tip-over switch, and overheat protection.
- Ideal For: Insulated small to medium greenhouses with electricity.
- Key Feature: Energy-saving auto-energy mode that adjusts output.
Best for Budget: Lasko Ceramic Tower Heater
A reliable and affordable oscillating tower heater. It provides good air circulation with multiple heat settings. While not waterproof, it’s a solid choice for a dry greenhouse environment on a budget.
Best Propane: Mr. Heater Buddy Indoor-Safe Portable Heater
This is a top pick for off-grid heating. It has a low-oxygen shut-off sensor and tip-over protection. Remember, you must crack a window or vent for fresh air exchange when using it.
- Ideal For: Unpowered hobby greenhouses or emergency backup heat.
Best Oil-Filled Radiator: De’Longhi Oil-Filled Radiator
This unit offers excellent, even heat for a stable environment. It’s completely silent and has multiple heat settings. Its thermal slots design maximizes heat radiation safely.
Essential Accessories For Efficient Heating
A heater alone isn’t a complete system. These tools maximize efficiency and plant safety.
Thermostat and Controller
A separate, digital thermostat is a game-changer. It turns your heater on and off automatically to maintain your exact desired temperature, preventing energy waste. Some advanced controllers can be managed from your phone.
Circulation Fans
Even with a fan heater, a small oscillating fan promotes air movement. This prevents mold, strengthens plant stems, and ensures even temperature distribution, taking strain off the heater.
Thermometers and Hygrometers
Never guess the temperature or humidity. Place a minimum-maximum thermometer at plant level to see your actual temperature range. A hygrometer helps you manage humidity levels, which heaters can affect.
Installation And Safety Setup Guide
Proper setup is crucial for safety and performance. Follow these steps.
- Choose the Right Location: Place the heater on a stable, level, non-flammable surface. Keep it away from water spills, plant foliage, and flammable materials like burlap.
- Secure Electrical Connections: Use a GFCI (Ground Fault Circuit Interrupter) outlet for any electric heater. Use outdoor-rated, heavy-duty extension cords if absolutely necessary, but a dedicated outlet is better.
- Ensure Proper Ventilation: For propane heaters, provide a fresh air inlet. For all heaters, some air exchange is needed to prevent excessive humidity buildup, which encourages disease.
- Install Heat Distribution: If using a non-fan heater, consider a small, low-speed fan to gently move the warm air around the greenhouse.
- Test Your System: Before a cold night arrives, test your heater and thermostat. Monitor the temperature gradient from floor to ceiling and corner to corner.
Energy Efficiency And Cost Saving Tips
Heating can be expensive. These strategies reduce your bill and environmental impact.
Improve Insulation First
The cheapest heat is the heat you don’t lose. Seal all gaps and cracks with weather stripping. Install bubble wrap or horticultural fleece on the interior walls. This single step can cut your heating needs by up to 30%.
Use Thermal Mass
Thermal mass absorbs heat during the day and releases it at night. Place black-painted water barrels or stacks of pavers inside. They act like a battery, stabilizing temperatures.
Implement Zonal Heating
Instead of heating the entire space, use a heat mat for seed trays or a small radiant heater for your most tender plants. This targeted approach uses far less energy.
Maintain Your Equipment
Clean heater filters and fans regularly. Dust buildup makes the heater work harder, reducing efficiency and becoming a fire hazard. Check seals on propane connections annually.
Troubleshooting Common Heating Problems
Even with a good setup, issues can arise. Here’s how to fix them.
Problem: Heater runs constantly but temps stay low.
Solution: Your heater is likely undersized. Check your BTU calculation. Also, inspect for major insulation issues or drafts you may have missed.
Problem: Condensation is excessive on walls and plants.
Solution: This is common with propane heaters or in tightly sealed spaces. Increase ventilation slightly during the day to allow moist air to escape. A dehumidifier can help in very humid climates.
Problem: Temperature swings are too dramatic.
Solution: Your thermostat might be in a poor location (in direct sun or a cold draft). Relocate it to plant level in a shaded area. Also, adding more thermal mass will buffer these swings.
Seasonal Maintenance Checklist
Keep your heating system reliable with this simple annual maintence schedule.
- Before Winter: Test heater operation, clean all components, check electrical cords for damage, stock fuel if needed, and verify thermostat batteries.
- During Winter: Monitor fuel levels, clear snow from vents and solar panels, and check for ice damage to seals.
- After Winter: Give the heater a final cleaning before storage. Drain any water barrels used for thermal mass to prevent mosquito breeding. Inspect the greenhouse structure for any damage from winter storms.
FAQ Section
What size heater do I need for a 6×8 greenhouse?
First, find the cubic footage. For an average 7-foot height, that’s 6 x 8 x 7 = 336 cubic feet. Multiply by 25 BTUs: 336 x 25 = 8,400 BTUs. Look for a heater rated around 8,000-9,000 BTUs.
Can I use a home space heater in my greenhouse?
You can, but choose carefully. Standard home heaters often lack the durability for humid conditions. Ensure it has the safety features listed earlier and is rated for slightly damp environments. Never use one with a damaged cord.
How can I heat a small greenhouse without electricity?
Propane heaters are the primary option. Passive methods include using thermal mass (water barrels) and insulating exceptionally well. Some gardeners use compost piles or solar heat sinks, but these are less reliable in deep winter.
Is it safe to leave a greenhouse heater on all night?
Yes, if it is designed for that purpose and has automatic safety shut-offs. Using a thermostat is essential for this. Always follow the manufacturer’s instructions and ensure the area around the heater is clear of debris.
Do greenhouse heaters dry out the air?
Electric fan heaters can reduce humidity. Propane heaters add water vapor to the air as a byproduct of combustion. Monitor humidity with a hygrometer. If air gets too dry, you can place trays of water near the heater to add moisture.
Selecting the right heater protects your investment in plants and structure. By matching the heater to your specific needs, prioritizing safety, and implementing efficiency tips, you can maintain a productive small greenhouse year-round. Start by measuring your space and assessing your power options, then choose a reliable model from the categories discussed. Your plants will thank you with robust growth, even on the coldest days.