The Ultimate Guide to Greenhouse Heaters: Stay Warm & Grow All Year Long
The dream of every passionate gardener is a lush, thriving oasis, regardless of the season. You’ve invested in a greenhouse to protect your precious plants from the elements, but when the mercury plummets, a critical question arises: is the greenhouse itself enough? For most of us in the U.S., the answer is a chilly “no.”
Welcome to the definitive guide on greenhouse heating. We’re here to demystify the process and answer all those burning questions you’ve been searching for, like “how much electricity do they use?” and “what’s the best heater for my space?” Let’s turn your seasonal garden into a year-round paradise.
Do You Actually Need a Heater in Your Greenhouse?
First things first: can you get away without one? The short answer is, it depends. But for most American gardeners aiming for continuous growth, a heater isn’t a luxury—it’s an essential tool. Here’s how to decide:
- Your Climate Zone: If you live anywhere that experiences freezing temperatures (most of the continental U.S.), you’ll need a heater to keep your plants alive, let alone thriving. Gardeners in USDA Zones 7 and below should consider a heater mandatory for winter cultivation. Even in Zones 8 or 9, an unexpected cold snap can wipe out an entire season’s work.
- Your Plants of Choice: Are you growing hardy winter greens like kale and spinach, or are you dreaming of year-round tomatoes, orchids, and tropical citrus? Tender, warm-weather plants require consistent temperatures above 50-60°F to survive and produce. Frost-tolerant plants might survive a freeze, but they won’t grow.
- Your Greenhouse’s Insulation: A well-sealed, insulated greenhouse will retain heat far better than a drafty, single-pane structure. Polycarbonate panels are better insulators than glass. Adding a layer of bubble wrap insulation to the interior walls can significantly reduce heat loss, making your heating efforts more efficient and cost-effective.
What Kind of Heater is Best for a Greenhouse? A Complete Breakdown
Choosing a heater isn’t a one-size-fits-all decision. The “best” heater depends on your greenhouse size, power availability, budget, and the types of plants you’re growing. Let’s break down the most common types.
1. Electric Heaters: The Popular & Precise Choice
For the vast majority of hobbyist and small-scale greenhouse owners, electric heaters are the way to go. They are clean, easy to use, and offer precise temperature control.
Pros:
- Safety: No open flames or harmful emissions like carbon monoxide. This is a huge advantage in an enclosed space.
- Ease of Use: Simply plug it in. No fuel to store or refill.
- Precise Control: Most come with built-in thermostats, allowing you to set and maintain the exact temperature your plants need. This prevents energy waste and ensures optimal growing conditions.
- Dry Heat: They don’t add extra moisture to the air, which helps prevent fungal diseases and mold—a common problem in humid greenhouses.
Cons:
- Operating Cost: Electricity can be expensive, especially if you live in an area with high utility rates and need to run the heater frequently.
- Power Dependency: Useless during a power outage, which can be disastrous during a winter storm.
Types of Electric Heaters:
- Forced-Air (Fan) Heaters: These are the most common. They use a heating element and a fan to quickly circulate warm air throughout the greenhouse. They’re great for rapid heating and ensuring even temperature distribution.
- Convection Heaters: These heat the air, which then rises and circulates naturally. They are silent and provide a gentle, even heat, but can be slower to warm up a large space.
- Radiant (Infrared) Heaters: These are highly efficient. Instead of heating the air, they emit infrared waves that heat objects directly—your plants, pots, benches, and the floor. This is similar to how the sun warms the earth. The objects then radiate heat back into the space. They are excellent for targeted heating and can save energy.
2. Gas Heaters (Propane & Natural Gas): The Powerhouse Option
For large greenhouses or those without reliable access to electricity, gas heaters are a powerful and often more economical solution for heating large volumes of space.
Pros:
- High Heat Output: They produce a significant amount of BTUs, making them ideal for large or poorly insulated greenhouses.
- Cost-Effective to Run: In many areas, natural gas or propane is cheaper per unit of heat (BTU) than electricity.
- Power Outage Proof: They operate independently of the electrical grid, providing peace of mind during winter storms.
Cons:
- Ventilation is CRITICAL: They produce carbon monoxide and other harmful gases. You must have proper ventilation, either through a dedicated vent kit or by using an externally vented model. Never use an unvented gas heater designed for indoor use in a sealed greenhouse.
- Produce Moisture: A byproduct of burning propane or natural gas is water vapor. This increases humidity, which can be beneficial for some plants but also encourages mold and fungal diseases if not managed with good air circulation.
- Installation Complexity: Natural gas heaters require professional installation. Propane heaters require you to manage and replace heavy tanks.
3. Kerosene/Paraffin Heaters: The Old-School Backup
While less common today, kerosene heaters still have a place as an emergency or supplemental heat source. They are portable and don’t require electricity. However, their drawbacks are significant.
Pros:
- Inexpensive: Low initial purchase price.
- Portable: Easy to move around as needed.
Cons:
- High Moisture & Odor: They release a lot of water vapor and can have a strong smell.
- Safety Risks: Open flames present a fire hazard. They also consume oxygen and release pollutants, so ventilation is absolutely essential.
- Manual Operation: Most lack thermostats, requiring you to monitor and adjust them manually.
Top Greenhouse Heater Picks for 2025
Navigating the market can be tough. Based on our experience and extensive research, here are three top-performing heaters available on Amazon that cater to different needs.
BIO GREEN PAL 2.0/US Electric Fan Heater
This is the workhorse of greenhouse heaters. It’s specifically designed for damp environments with a splash-proof rating (IPX4). The powerful fan ensures excellent air circulation, and its precise thermostat maintains temperature within a tight range. It’s durable, reliable, and perfect for small to medium-sized hobby greenhouses (up to 120 sq. ft.).
Check Price on Amazon
Mr. Heater F232000 MH9BX Buddy Propane Heater
The Mr. Heater Buddy is a legend for a reason. It’s the perfect solution for off-grid greenhouses or as a robust backup for power outages. With features like an oxygen depletion sensor and tip-over shut-off, it’s one of the safest propane options available. Remember to always ensure you have a source of fresh air (like a cracked vent) when using it.
Check Price on Amazon
Vornado AVH10 Vortex Heater with Auto Climate Control
While not a “greenhouse-specific” heater, the Vornado excels at one crucial thing: moving air. Its signature vortex action circulates heat evenly throughout the entire space, eliminating hot and cold spots. It has advanced safety features and an intelligent thermostat that automatically adjusts heat output, making it surprisingly efficient.
Check Price on AmazonThe Cost Factor: How Much Electricity Does a Greenhouse Heater Use?
This is the million-dollar question for anyone considering an electric heater. The fear of a shocking utility bill is real, but it’s also manageable and predictable. Let’s break down how to calculate the cost.
The Simple Formula for Calculating Your Cost:
All you need are three numbers: your heater’s wattage, how many hours you expect it to run per day, and your electricity rate from your utility provider (found on your bill, usually in cents per kilowatt-hour or kWh).
- Convert Watts to Kilowatts (kW): Divide your heater’s wattage by 1000. (e.g., 1500 watts / 1000 = 1.5 kW).
- Calculate Daily Energy Use (kWh): Multiply the kW by the number of hours the heater runs. (e.g., 1.5 kW * 8 hours = 12 kWh).
- Calculate Daily Cost: Multiply the daily kWh by your electricity rate. (e.g., 12 kWh * $0.17/kWh = $2.04 per day).
Monthly Cost: Simply multiply the daily cost by 30. (e.g., $2.04 * 30 = $61.20 per month).
Estimated Monthly Cost Comparison
Let’s see how this plays out in a real-world scenario. The table below estimates the monthly cost based on an average U.S. electricity rate of $0.17 per kWh. Remember, a heater with a thermostat won’t run continuously; it will cycle on and off. These estimates are based on an average runtime of 8 hours per day.
| Heater Wattage | Kilowatts (kW) | Est. Daily Cost (8 hrs) | Est. Monthly Cost |
|---|---|---|---|
| 750W (Low Setting) | 0.75 kW | $1.02 | $30.60 |
| 1500W (High Setting) | 1.5 kW | $2.04 | $61.20 |
| 2000W (Heavy Duty) | 2.0 kW | $2.72 | $81.60 |
As you can see, the costs can add up. This brings us to the most important part of greenhouse heating…
Beyond the Heater: The Greenhouse Heating System
An efficient heating “system” is about more than just the heater itself. To keep costs down and your plants happy, you need to think holistically.
1. Insulation is Your Best Friend
The #1 way to reduce your heating bill is to stop heat from escaping. A heater in a drafty greenhouse is like pouring water into a bucket with a hole in it.
- Seal the Gaps: Use weather stripping or silicone caulk on all joints, doors, and vents to eliminate drafts.
- Add Insulation: For glass or single-wall polycarbonate greenhouses, adding a layer of horticultural bubble wrap to the inside walls and roof can cut heat loss by up to 50%.
- Thermal Mass: Place large barrels of water (painted black) inside your greenhouse. They will absorb solar heat during the day and slowly release it at night, naturally stabilizing the temperature.
2. A Thermostat is Non-Negotiable
Running a heater without a thermostat is a massive waste of energy and can even harm your plants by overheating them. A thermostat acts as the brain of your heating system, turning the heater on only when the temperature drops below your set point and shutting it off once that temperature is reached. This simple device can easily cut your energy consumption in half compared to a continuously running heater. For the most accurate readings and control, consider investing in one of the best greenhouse heaters with a built-in thermostat. A reliable thermostat ensures you’re only paying for the heat you actually need.
3. Don’t Forget Air Circulation
Hot air rises. Without proper circulation, the top of your greenhouse can be toasty warm while the soil level remains dangerously cold. A small, oscillating fan set on low will:
- Distribute heated air evenly.
- Prevent moisture from settling on leaves, reducing disease risk.
- Strengthen your plants’ stems.
Frequently Asked Questions (FAQ)
Q: Can I use a regular indoor space heater in my greenhouse?
A: You can, but with caution. Look for models with essential safety features like tip-over protection and an automatic overheating shut-off. However, greenhouse-specific heaters are superior because they are built to withstand the high humidity and moisture levels of a greenhouse environment (look for an IPX4 rating or higher). Regular space heaters may corrode or short-circuit over time in these conditions.
Q: What’s the most energy-efficient type of electric heater?
A: Technically, all 1500W electric heaters convert the same amount of electricity into 1500W of heat. The difference is in how they deliver that heat. Infrared (radiant) heaters are often considered the most “efficient” in practice because they heat your plants and soil directly, not the air. This means less energy is wasted heating empty space, especially in a leaky greenhouse. However, in a well-insulated and sealed greenhouse, a fan heater with good circulation and a precise thermostat can be just as effective.
Q: How do I figure out what size heater I need?
A: You can use a simple formula to get a good estimate. You’ll need to calculate the cubic feet of your greenhouse (Length x Width x Average Height). Then, determine the maximum temperature rise you’ll need (your desired minimum indoor temp minus the coldest expected outdoor temp).
Formula: Cubic Feet x Desired Temperature Rise (°F) x 0.133 = BTUs needed per hour.
To convert BTUs to watts, divide the BTU number by 3.41. (e.g., 5000 BTUs / 3.41 ≈ 1466 Watts). This would mean a standard 1500W heater is a perfect fit.
Your Year-Round Garden Awaits
Heating your greenhouse opens up a new world of gardening possibilities, transforming it from a seasonal shelter into a year-round engine of growth. While the initial setup and running costs can seem daunting, the solution is knowledge.
By choosing the right type of heater for your needs, accurately calculating its size, and—most importantly—creating an efficient system with proper insulation and temperature control, you can protect your plants and your wallet. The joy of harvesting a fresh tomato in the middle of January is a reward that makes it all worthwhile. Happy growing!
