Best Propane Greenhouse Heaters for Plant Protection

Keeping a greenhouse warm during cold spells requires a heater that is reliable, safe, and matched to the space. The table below summarizes five propane heater options that gardeners commonly consider for greenhouse use, showing their key characteristics at a glance.

Product	Type	BTU Range	Intended Use
Mr. Heater MHVFBF20LPT	Vent-Free Blue Flame Wall Heater	20,000 BTU	Indoor rooms, unvented greenhouses
Mr. Heater 4000-18000 BTU	Portable LP Gas Heater (Dual Tank Capable)	4,000–18,000 BTU	Medium greenhouses, portable setups
Mr. Heater Portable Buddy MH9BX	Portable Radiant Heater	4,000–9,000 BTU	Small greenhouses, seedling areas
15,000 BTU Single Tank Top Heater	Tank-Top Radiant Heater	10,000–15,000 BTU	Compact to mid-size greenhouses
Avenger FBDTP15 Infra-Red Tank Top	Infrared Tank-Top Outdoor Heater	15,000 BTU	Well-ventilated greenhouses or covered outdoor areas

Mr. Heater 20,000 BTU Blue Flame Vent Free

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This Mr. Heater model is a vent-free blue flame wall heater that offers up to 20,000 BTUs, suitable for heating larger greenhouses or attached cold frames designed to retain indoor air. It includes a built-in thermostat for temperature control and a battery-powered electronic ignition for startup convenience. The unit is rated for use at elevations up to 4,500 ft and has an Oxygen Depletion Sensor (ODS), which automatically shuts the heater down if oxygen levels fall below safe limits.

For greenhouse application, the vent-free design delivers heat evenly into the air and reduces installation complexity compared with vented systems. Installation must follow local codes and greenhouse ventilation plans because vent-free appliances release combustion byproducts into the space; proper oxygen monitoring and fresh-air strategies are important for plant health and safety.

Mr. Heater 4,000–18,000 BTU Portable LP Heater

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This variable-output Mr. Heater provides 4,000, 9,000, or 18,000 BTU settings and supports larger propane tanks with an additional hose and filter, which can be useful for extended greenhouse heating. The single-control knob and piezo igniter simplify operation. The manufacturer lists a possible heat range up to 450 sq. ft., which helps when sizing for greenhouse volume and insulation.

The unit features an automatic tip-over shutoff for safety and is intended for both indoor and outdoor use when installed per instructions. Its adjustable output makes it adaptable to fluctuating nighttime lows versus daytime sunlight gains, giving growers a way to modulate fuel use based on actual needs.

Mr. Heater Portable Buddy MH9BX 4,000–9,000 BTU

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The Portable Buddy is a compact radiant heater delivering 4,000–9,000 BTUs and designed for direct, sun-like infrared heat. It heats objects and plants directly rather than primarily warming the air, which can be beneficial in small greenhouses or seedling bays where targeted warmth prevents foliage chill.

Safety upgrades include an improved tip-over switch and a Piezo igniter that requires no batteries. The unit is rated for indoor-safe operation under specified conditions, but growers should ensure adequate ventilation and CO monitoring when used in enclosed greenhouse spaces.

15,000 BTU Single Tank Top Portable Heater

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This tank-top radiant heater mounts directly onto a 20 lb propane tank and offers three regulator settings (15,000–12,500–10,000 BTUs), providing portable heating that’s simple to position inside a greenhouse. The tip-over safety shutoff is a standard feature to reduce accident risk when used near benches and plant traffic areas.

As a radiant heater, it warms surfaces and plants quickly, which can preserve root-zone warmth while overall air temperatures remain lower. The design is useful for growers who need temporary supplemental heat in specific zones rather than whole-structure heating.

Avenger FBDTP15 Infra-Red Tank Top 15,000 BTU

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The Avenger tank-top unit provides 15,000 BTU infrared heating with three heat settings and a swivel burner head for directional warmth. Its durable wire guards and straightforward tank hookup make it a common choice for camping and patio heating, and some growers use it in well-ventilated greenhouse setups or covered outdoor seed areas.

Because the manufacturer recommends outdoor use, greenhouse deployment needs careful assessment of ventilation and combustion gas management. Where used, its infrared technology can protect plant tissue by delivering heat directly to surfaces and benches.

Buying Guide: Choosing A Propane Greenhouse Heater

Choosing the right propane heater for a greenhouse involves balancing heat output, heater type, safety features, fuel logistics, and greenhouse characteristics. Below are the key considerations and comparative perspectives to guide a selection.

1. Heater Type: Blue Flame / Vent-Free vs Radiant vs Infrared

• Blue Flame / Vent-Free: Produces even air heating and is efficient for whole-space warming. Because combustion products are released into the greenhouse, you must manage ventilation and oxygen levels; ODS sensors are essential.
• Radiant (Tank-Top / Portable): Heats objects and bench surfaces directly. Good for spot heating around sensitive plants and seedlings. Often simpler to move and set up but less suited for full-space uniformity.
• Infrared: Targets plant surfaces and can reduce humidity-related fungi by keeping surfaces warm. Some infrared units are rated outdoor-only; check manufacturer guidance for greenhouse use and ensure ventilation if used inside.

2. Sizing: BTU And Greenhouse Heat Load

Calculate approximate BTU needs by factoring greenhouse volume, insulation (single layer poly vs double wall polycarbonate), heat loss through glazing, nighttime temperature targets, and local climate lows. As a rough guide:

• Small, well-insulated mini-greenhouse: lower BTU needs (4,000–9,000)
• Medium greenhouse with moderate insulation: mid-range BTUs (10,000–18,000)
• Large or poorly insulated greenhouse: higher BTU units or multiple heaters (15,000–20,000+)

For precision, perform a heat loss calculation (U-values, square footage, temperature differential) or consult a greenhouse heating specialist.

3. Safety Features To Prioritize

• Oxygen Depletion Sensor (ODS): Critical for vent-free units to shut off if oxygen levels drop.
• Tip-Over Shutoff: Important for portable tank-top and buddy heaters to prevent fires if the unit falls
• Automatic Shutoff For Overheat/Flame Out: Adds protection when combustion becomes unstable
• Proper Placement: Keep heaters away from flammable materials, clearances per manufacturer, and outside the plant canopy when possible.

4. Fuel Logistics And Runtime

Consider propane tank size, availability, and consumption rates. Tank-top heaters attach directly to 20 lb cylinders making them portable, while larger or vented systems may be plumbed to bulk tanks. Estimate runtime by dividing tank capacity by the heater’s fuel consumption; higher BTU settings use fuel faster. For extended cold snaps, plan for resupply or larger tanks.

5. Ventilation And Combustion Gas Management

Vent-free units introduce combustion products like water vapor and low levels of CO2 and CO into the space. Ensure greenhouse ventilation strategies: trickle vents, louvers, or scheduled fresh-air exchange. Monitor for condensation and mold risks; excess humidity from combustion can affect plant health.

6. Control Options And Temperature Accuracy

• Built-In Thermostats: Allow automatic cycling to maintain setpoints; important to avoid temperature swings that stress plants.
• External Thermostats / Controllers: Provide more precise control and can integrate with timers, sensors, or remote monitors.
• Variable Output: Heaters with multiple BTU settings or modulating controls let growers match heat output to changing conditions, saving fuel.

7. Impact On Plant Physiology

Heaters that warm plant surfaces (radiant/infrared) can reduce frost damage without raising air temperature excessively. However, maintaining moderate air movement and avoiding hot spots is necessary to prevent uneven growth. For humidity-sensitive crops, managing the additional moisture from combustion is essential.

8. Installation, Codes, And Manufacturer Guidance

Follow local building and fuel codes when mounting wall or vent-free heaters. Some vent-free appliances are restricted in certain jurisdictions or commercial greenhouse applications. Always review manufacturer instructions, clearances, and approved use-cases for greenhouse environments.

9. Comparative Perspectives

• Efficiency vs Safety: Vent-free units are efficient for whole-space heating but require stricter ventilation and monitoring. Radiant units are safer for targeted heat but may be less efficient for larger volumes.
• Portability vs Permanence: Tank-top and portable units offer flexibility and lower installation cost. Wall-mounted vent-free heaters provide stable, permanent heating with thermostat control.
• Cost Of Operation: Higher BTU options heat faster but consume more fuel. Variable output units enable fuel savings when extremes are not present.

10. Practical Tips For Greenhouse Use

• Place heaters where they can warm benches and plant surfaces, not directly under leaves to avoid burning.
• Use reflective surfaces or thermal mass (water barrels, concrete) to store heat and reduce cycling.
• Combine passive measures (insulation, double layers, thermal curtains) with active heating to lower required BTU capacity.
• Install CO and temperature monitoring alarms when using combustion heaters in enclosed spaces.

Selecting the right propane greenhouse heater depends on greenhouse size, insulation, ventilation capability, and whether you need whole-space or targeted warming. Prioritize safety features and control precision, and verify manufacturer recommendations for greenhouse conditions before installation.