6 Best Propane Greenhouse Heaters For Supplemental Heat to Beat the Frost
Protect your greenhouse from frost with supplemental propane heat. We review the 6 best models for efficiency, safety, and reliable plant protection.
You check the forecast and your heart sinks; an unseasonable frost is coming tonight, and your tomatoes are just starting to blush. All that work, all that anticipation, is suddenly at risk. This is the moment every gardener dreads, where a single cold snap can wipe out months of effort.
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Why Propane is a Top Choice for Frost Protection
Propane is the go-to fuel for many of us for one simple reason: it’s a self-contained, powerful source of heat that doesn’t depend on your home’s electrical grid. When a cold front brings gusty winds and a power outage, your electric heater becomes a useless piece of plastic. A propane heater, however, will keep running, providing a reliable buffer between your plants and the killing frost.
The real advantage is the on-demand, high-heat output. Unlike electric heaters that struggle to keep up with rapidly dropping temperatures, a propane unit can quickly raise the ambient temperature in a greenhouse by 10, 20, or even 30 degrees. This isn’t about keeping your greenhouse tropical all winter; it’s about providing a powerful, short-term blast of heat to survive a critical cold spell.
Of course, there’s a tradeoff. Burning propane produces carbon dioxide, water vapor, and other combustion byproducts. While a little extra CO2 can be good for plants, too much moisture can invite mold and mildew. More importantly, incomplete combustion can produce carbon monoxide, so ventilation and a CO detector are non-negotiable safety measures with any unvented option.
Mr. Heater Buddy: The Ultimate Portable Solution
Almost everyone starts with a Mr. Heater Buddy, and for good reason. It’s small, affordable, and runs on the same 1 lb propane canisters you use for camping. This makes it incredibly easy to grab from the garage and fire up at a moment’s notice when you see an unexpected frost warning. It’s the perfect emergency tool.
Its best features are built-in safety mechanisms. The low-oxygen shutoff sensor (ODS) and tip-over switch provide essential peace of mind. You can place it in your 8×10 greenhouse to save your seedlings and not worry about it becoming a hazard overnight. It’s a simple, effective solution for small spaces and temporary needs.
Don’t mistake it for a permanent heating system, though. The Buddy heater is designed for attended use and isn’t meant to run for days on end. It’s fantastic for taking the edge off a cold night or two, but it lacks the power and fuel capacity for consistently heating anything larger than a small hobby house through a deep freeze.
Dyna-Glo Pro: Power for Larger Hobby Greenhouses
When you need raw, overwhelming power to heat a larger space fast, you bring in a forced-air heater like the Dyna-Glo Pro. Often called "salamander" or "torpedo" heaters, these units are basically a jet engine for heat. They can blast out tens of thousands of BTUs, making them ideal for quickly warming up a large hoop house before a sudden temperature drop.
Think of this as a temporary, emergency-use tool, not a subtle climate controller. It connects to a 20 lb or larger propane tank and will absolutely save a crop from a hard frost. You can take a 20×40 hoop house from freezing to a safe 45°F in a surprisingly short amount of time.
However, this power comes with significant downsides. These heaters are loud, burn through propane at an astonishing rate, and pump a massive amount of moisture and exhaust directly into your greenhouse. They are unvented and require serious attention to ventilation. Use them to win the battle against a specific frost event, but don’t plan on using one for your season-long heating strategy.
Camco Olympian Wave: Efficient Catalytic Heating
Catalytic heaters like the Camco Olympian Wave are a different beast entirely. Instead of a visible flame, they use a chemical reaction with a platinum-coated mat to produce powerful, radiant heat. This process is incredibly efficient, using significantly less propane to generate the same amount of warmth as a traditional flame-based heater.
The heat they produce is radiant, meaning it heats objects directly—your benches, pots, and plants—rather than just the air. This is a more effective and gentle way to protect plants from cold. Because there’s no flame, they are also exceptionally quiet and produce far fewer harmful byproducts than other unvented heaters.
The main considerations are the higher upfront cost and the need for some fresh air circulation, as they still consume oxygen. They also don’t create the hot "blast" of air that a forced-air unit does, so they raise the temperature more slowly and evenly. For the hobbyist looking for a safe, quiet, and highly efficient solution for a small to medium greenhouse, a catalytic heater is a superb choice.
Modine Hot Dawg: A Permanent Vented Powerhouse
When you decide to get serious about year-round or extended-season growing, you graduate to a vented unit heater like the Modine Hot Dawg. This isn’t a portable, temporary fix; it’s a permanent piece of infrastructure. You hang it from the ceiling, run a gas line to it, and vent all the exhaust safely outside the greenhouse.
The benefits are immense. Because it’s vented, you get clean, dry heat with zero combustion byproducts entering your growing space. This eliminates any risk of carbon monoxide exposure and prevents the excessive humidity that unvented heaters create. Hooked up to a thermostat, it becomes a true "set it and forget it" system, automatically kicking on to maintain a minimum temperature without any intervention.
The tradeoff is obvious: cost and complexity. This is a significant investment that requires proper installation, including running gas lines and cutting a hole for the vent pipe. It’s overkill for someone just trying to prevent frost on a few tomato plants in May, but for a dedicated hobby farmer with a permanent greenhouse, it’s the gold standard for safety and reliability.
Mr. Heater Big Maxx: Reliable Vented Unit Heater
Much like the Modine, the Mr. Heater Big Maxx series represents a serious commitment to greenhouse climate control. It’s another top-tier choice for a permanently installed, power-vented unit heater. It provides the same core benefit: safely exhausting all harmful fumes and moisture outside while delivering powerful, thermostatically controlled heat inside.
Choosing between a Big Maxx and a Hot Dawg often comes down to local availability, specific BTU model features, and price. Both are workhorses designed for garages and workshops, which makes them durable enough to handle the humid environment of a greenhouse. They are built to last and provide reliable, automated frost protection for years.
Again, this is a solution for a well-established, permanent structure. You’ll need to factor in the cost of the unit, professional installation, and a large propane tank. But the peace of mind that comes from knowing your greenhouse is protected by a safe, automated system is often worth every penny for the serious grower.
ProCom Ventless Heater: Great Space-Saving Option
A wall-mounted ventless heater, like those from ProCom, occupies a smart middle ground. It offers more power and permanence than a portable Buddy heater but without the cost and complexity of a fully vented unit. These slim-profile heaters mount directly to a wall, saving precious floor space in a crowded greenhouse.
These units typically connect to a larger propane tank and often come with a built-in thermostat and an oxygen depletion sensor (ODS) for safety. They provide consistent, reliable heat and are a great "good enough" solution for many hobbyists. They can easily keep a well-sealed 10×12 or larger greenhouse above freezing through most cold snaps.
The key thing to remember is that "ventless" does not mean "zero-impact." It still combusts fuel inside the greenhouse, releasing CO2 and water vapor. You absolutely must ensure you have adequate passive ventilation—like a cracked roof vent or window—to allow for fresh air exchange. It’s a fantastic option, as long as you respect its ventilation requirements.
Choosing Your Heater: BTU, Vents, and Safety
Making the right choice comes down to balancing three key factors for your specific situation. Don’t just buy the most powerful heater; buy the right heater. It’s about matching the tool to the job.
First, consider the power, measured in BTUs (British Thermal Units). A tiny 6×8 polycarbonate greenhouse might only need 4,000 BTUs to stay above freezing, while a 20×40 hoop house with single-layer plastic could require 40,000 BTUs or more on a cold, windy night. A rough rule of thumb is to calculate the surface area of your greenhouse walls and roof, multiply by the desired temperature increase, and then multiply by a factor for heat loss (e.g., 1.2 for double-wall poly, 1.5 for single-layer). This gives you a starting point.
Next, decide on your ventilation strategy.
- Vented Heaters: The safest option. All exhaust goes outside. Best for air quality and plant health. Requires permanent installation and higher cost.
- Unvented (Vent-Free) Heaters: More affordable and portable. They release moisture and exhaust into the greenhouse. Requires a source of fresh air and a carbon monoxide detector is mandatory.
Finally, prioritize safety. Never compromise here. Look for heaters with an Oxygen Depletion Sensor (ODS) that shuts the unit off if oxygen levels get too low. A tip-over switch is essential for any portable unit. And no matter which heater you choose, install a battery-operated carbon monoxide (CO) detector in your greenhouse. It’s a cheap insurance policy that could save your life.
Ultimately, the best propane heater is the one that fits your greenhouse size, your budget, and your willingness to manage it. Whether it’s a small portable unit for emergencies or a permanent vented system for season-long peace of mind, being prepared is what separates a successful harvest from a heartbreaking loss. The right heater turns a season-ending threat into just another chilly night.
