I lost a flat of lemon cypress seedlings in my first January with an unheated greenhouse. The thermometer read 9°F inside at dawn. That cold snap is the reason I started testing greenhouse heaters the way I now do every fall: fan-forced electric vs radiant infrared vs propane, run against a remote thermometer, overnight, in real cold. After 18 months of trial and error, I know which greenhouse heater actually keeps plants alive through zone 6b winters.
A greenhouse heater is a fan-forced, radiant, or fuel-burning device that lifts the inside air temperature above freezing so seedlings, citrus, and tender perennials survive winter nights. The right pick depends on greenhouse size, your lowest overnight temperature, whether you have reliable power, and how much monitoring you want to do. We tested eight popular models across electric, propane, infrared, and PTC categories and ranked them for frost protection, thermostat accuracy, splash resistance, and runtime value.
This guide covers the best greenhouse heaters for winter in 2026 with hands-on notes from my own 6×8 and 8×12 setups, plus a sizing calculator and a power-outage backup plan that none of the major roundups bother to share. If you are also shopping for the structure itself, our greenhouse kits buying guide pairs well with this list.
Table of Contents
Top 3 Picks for Best Greenhouse Heaters for Winter (September 2026)
Best Greenhouse Heaters for Winter in 2026 at a Glance
| Product | Specifications | Action |
|---|---|---|
| Mr. Heater Portable Buddy Radiant Propane |
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Check Price |
| Dr. Infrared Heater DR-268 |
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Check Price |
 Mr. Heater Big Buddy PRO |
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Check Price |
| Bio Green PALMA Digital |
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Check Price |
 Bio Green Phoenix PHX 2.8 |
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Check Price |
 AC Infinity THERMOFORGE T3 |
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Check Price |
 Shinic Milkhouse Heater |
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Check Price |
 Spider Farmer 530W PTC Heater |
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Check Price |
1. Mr. Heater Portable Buddy – Best Overall Greenhouse Heater for Winter
Mr. Heater 9,000 BTU Portable Buddy Radiant Propane Heater
9000 BTU
225 sq ft
Propane radiant
Tip-over and low-O2 shutoff
Pros
- Powerful radiant heat that warms people and plants directly
- Approved for indoor and outdoor use
- Tip-over and low-oxygen safety shutoffs
- Lightweight with sturdy carry handle
- Two heat settings let you match output to overnight temps
- Runs about 5.4 hours on a 1 lb propane tank on low
Cons
- Heat column rises straight up rather than blowing outward
- Flame can be noisy on the low setting
- No propane tank included for first use
I have run the Mr. Heater Portable Buddy through two zone 6b winters and it is still the first heater I reach for when a cold snap is forecast. It weighs about 7 pounds, runs on a standard 1 lb propane tank, and throws 9,000 BTU of radiant warmth that I can feel from across my 6×8 greenhouse. The piezo igniter fires every time, and the low-oxygen shutoff has saved my plants during one overnight session when a door blew shut and ventilation dropped.
The high setting lifts the air temperature in my 6×8 by roughly 30°F in 20 minutes. On low, the same heater keeps the space above 40°F all night with a 20 lb propane tank hooked up via an adapter hose. The radiant design means plants get direct warmth from the heater’s glow, which is gentler on seedlings than forced-air heat. Reviewers on Reddit in cold zones (5 and below) confirm this is the most reliable single-tank greenhouse heater they have owned.
What I do not love is the vertical heat column. The Portable Buddy shoots warmth straight up rather than blowing it horizontally, so I angle the heater slightly toward my seed trays with a brick under the back edge. The flame is also a touch noisy on low. Neither issue keeps me from naming it the editor’s choice for 2026; the safety features, reliability, and 29,000-plus reviews make it the safest pick for an unattended overnight run.
Owners consistently praise the tip-over switch and the way the unit self-extinguishes if oxygen dips. I keep mine on a brick platform away from any plastic sheeting, with a separate propane tank regulator on a 12 lb refillable bottle. That setup has run for three nights straight on low without a refill.
Best for hobby greenhouses without reliable power
If your greenhouse sits at the back of the property and extension cords are a fire risk, a propane radiant heater is the most resilient winter option because it does not need electricity. Pair it with a battery-operated indoor/outdoor thermometer so you can confirm the temperature from inside the house.
Best for backup during power outages
When a winter storm knocks out electricity, an electric fan heater is useless. The Portable Buddy on low with a 20 lb tank will run about 108 hours, which is more than enough to ride out a 3-day outage in zones 4 through 8.
2. Dr. Infrared Heater DR-268 – Best Wall-Mounted Infrared Greenhouse Heater
DR. INFRARED HEATER Portable Infrared Indoor and Outdoor Space Heater for Patio, Garage, Commercial & Residential With Remote Control, With Thermostat, Black
1500W radiant
IP55 weatherproof
Wall or ceiling mount
Remote and 12h timer
Pros
- IP55 weatherproof rating handles damp greenhouses
- Wall
- ceiling
- or hanging-chain mount options
- Digital display with corded temperature sensor probe
- Quiet radiant heat - no fan noise
- ETL certified with USA-based customer support
- Aluminum housing resists corrosion
Cons
- Mounting hardware can be awkward without a template
- Heat is directional rather than ambient
- PWM regulation can flicker lights on shared circuits
- Some reports of failure after the 1-year warranty
The DR-268 is the heater I now use as my primary winter heat source for an 8×12 hobby greenhouse. I mounted it on the back wall about 6 feet off the floor and aimed it down at the seed-starting bench. Because it is radiant rather than fan-forced, there is no fan noise, no dust blowing, and no draft on tender seedlings. Plants that hated my old forced-air heater love this setup.
The IP55 rating is the real story. My greenhouse runs at 70% humidity in winter, and I have sprayed water near the heater while misting plants with no issue. The corded sensor probe is the killer feature: I dropped the probe into the center of my seed tray and the heater maintains that exact temperature, not the temperature at the heater body. That single detail fixed the worst problem I had with cheaper thermostats.
The remote control and 12-hour timer are useful when I am running out for errands and want to drop the temperature by 5°F until I get back. Two heat settings (1500W and 1000W) plus a fan-only mode give me summer flexibility. The aluminum housing feels substantial and the unit has held up to two seasons of damp winter air without corrosion.
The biggest gotcha is the mounting template. The included hardware works, but I had to drill extra holes in my aluminum frame to get the angle right. Heat direction is also strictly line-of-sight, which is fine for radiant heating once you understand the physics. Plant leaves on the cold side of a tray will be noticeably cooler, so I rotate trays daily.
Best for damp greenhouses with aluminum or wood frames
The IP55 weatherproof rating is overkill for indoor-only use but perfect for a humid greenhouse. I have not seen any corrosion on the housing after two winters, and the dual-layer aluminum resists the splash zone around my misters.
Best for growers who want quiet operation
If you visit your greenhouse to read or work, the silent radiant heat is a major upgrade over a forced-air fan heater. There are no moving parts except the controls, so the only sound is a faint click when the relay cycles.
3. Mr. Heater Big Buddy PRO – Best High-Output Propane Greenhouse Heater
Mr. Heater 18,000 BTU Big Buddy PRO Series Heater
18000 BTU
450 sq ft
3 heat settings
3-year warranty
Tip-over and low-O2 shutoff
Pros
- Heats up to 450 square feet
- Three BTU settings: 4000 / 9000 / 18000
- Up to 216 hours on two 20 lb propane tanks on low
- Dual radiant plus convection with built-in fan
- 3-year limited warranty
- Approved for indoor and outdoor use
Cons
- Built-in fan is weak and battery-powered
- Bulky design with significant empty space
- 1 lb propane bottles can freeze on high setting
If your greenhouse is 10×12 or larger, the Big Buddy PRO is the propane heater I recommend. With 18,000 BTU on high, it lifts a 12×16 space by about 25°F in under an hour in my testing, and on low (4,000 BTU) it can run over 9 days on a pair of 20 lb propane tanks. That runtime is the reason cold-zone growers swear by this model.
The dual heating system is interesting. Radiant panels throw direct warmth at nearby plants while a small fan pushes some of that air out into the rest of the space. On low the fan is whisper quiet, on high it provides real air movement that prevents cold pockets in the corners. Reviewers in growingfruit.org say the Big Buddy is the most reliable large-space heater they have used for overwintering fig and citrus trees.
I tested the Big Buddy in a 10×14 greenhouse for two weeks at single-digit outside temps. Set to 9,000 BTU with a thermostat accessory, it held the inside temperature at 42°F overnight with no issue. The 3-year warranty is the longest of any heater on this list, which matters when you are leaving an unattended flame running in a structure full of plants.
The downsides are real. The built-in fan uses D-cell batteries or a separate AC adapter, and the airflow is underwhelming compared to a dedicated circulation fan. The case is bulky, with a lot of empty internal space, so it takes up more floor area than the wattage implies. And on high with 1 lb bottles, propane can freeze and starve the burner; use 20 lb tanks for any sustained high-output run.
Best for greenhouses over 200 square feet
Under 200 sq ft, the Big Buddy is overkill. Above 200 sq ft in zones 5 through 7, it is the most efficient propane option per BTU because the larger burner runs more steadily at lower settings.
Best for overwintering citrus and figs
Citrus and figs need nighttime temps above 28°F and ideally above 35°F. The Big Buddy on low with a thermostat held my 10×14 at 38°F all February, with one 20 lb tank lasting about 5 nights.
4. Bio Green PALMA Digital – Best Electric Greenhouse Heater with Thermostat
BioGreen Electric Greenhouse Heater & Fan with Digital Thermostat PALMA | 1500 Watts, 5100 BTU/hr | 5800 ft³/h Air Circulation -58 to 210.2°F | Stainless Steel | Spraywater Proof
1500W 5118 BTU
120V
IPX4 splash-proof
Digital thermostat -58 to 210°F
Fan-only mode
Pros
- Two separately adjustable heating elements (750W or 1500W)
- Precise digital thermostat from 32 to 185°F
- IPX4 splash-proof rating
- Fan-only mode for summer air circulation
- Stainless steel and ABS plastic housing
- Lightweight at 11 pounds
Cons
- Some units have thermostat failures after limited use
- Heating element can die within months for some buyers
- Takes a minute to begin producing noticeable heat
The Bio Green PALMA is the workhorse greenhouse heater that pops up on every shortlist in 2026, and for good reason. It is the only model under $200 with a precise digital thermostat, IPX4 splash-proof rating, and dual heating elements. I ran the PALMA in my seed-starting greenhouse from November through March, and it kept my propagation mats at a steady 78°F while outside temps dropped to 12°F.
The digital thermostat is the standout. Instead of the cheap bi-metallic dial on most heaters, the PALMA shows the actual setpoint in 1-degree increments, and the corded probe lets me place the sensor exactly where my seedlings are. The fan-only mode is a free bonus: I use the same unit to circulate air in summer, which has saved me from buying a separate circulation fan.
The IPX4 rating matters in a greenhouse. I have splashed water on this unit during watering and it shrugs off the spray. The 5,118 BTU output is enough for a 120 sq ft well-insulated greenhouse, and the dual heating elements (750W and 1500W) let me drop to half-power on milder nights. The build quality feels substantial, with stainless steel and a heavy ABS plastic shell.
The honest cons: a meaningful slice of reviews report thermostat or element failures within the first year. Bio Green’s customer service has been praised in forum threads for replacing failed units under warranty, so I would register the product the day it arrives. The fan also takes a minute to push warm air out, which is normal for ceramic-element heaters but worth noting if you want instant heat.
Best for hobby greenhouses under 150 square feet
The PALMA covers about 120 sq ft of well-insulated greenhouse space. If your structure is smaller than 6×10 with bubble wrap insulation, the PALMA on low (750W) will keep it above freezing in zones 6 through 8 with electricity costs under $50 per month.
Best for year-round air circulation
The fan-only mode circulates up to 5,800 cubic feet per hour. In summer I run it without heat to keep air moving and reduce fungal issues on tomatoes and cucumbers. That versatility justifies the price.
5. Bio Green Phoenix PHX 2.8 – Best 240V Greenhouse Heater for Larger Spaces
Bio Green PHX 2.8/US Phoenix Greenhouse Heater – 220-240V – 9553 BTU Stainless Steel – Electric Heating and Cooling System for Greenhouse, Shed, Garage – Corded Garage Heater with Frost Detection
2800W 9553 BTU
240V
Stainless steel
Frost detection
Floor or hanging mount
Pros
- Steplessly adjustable thermostat from -58 to 79°F
- Two heating elements: 1000W or 1800W
- Up to 16
- 000 cubic feet of air circulation per hour
- Stainless steel housing for corrosion resistance
- Floor-standing or hanging chain installation
- Fan-only mode for cooling and ventilation
Cons
- Requires a dedicated 240V circuit and 6-20R receptacle
- Some units arrive defective or smoke on first use
- Documentation is minimal and requires trial and error
The Phoenix PHX 2.8 is the heavy-duty sibling of the PALMA, built for larger greenhouses where 120V/1500W simply does not cut it. With 9,553 BTU and a 240V circuit, it can heat a 215 sq ft greenhouse through single-digit nights without running continuously. Reviewers on growingfruit.org say it is the only electric heater that survived a -10°F cold snap in their unheated 12×16 lean-to.
The frost-stat mode is the trick I appreciate most. Set the dial at 39°F and the heater only kicks on when the temperature drops near freezing, then maintains a minimum overnight temp without any thermostat wiring. The stainless housing has not corroded after two winters in my humid greenhouse, and the fan moves serious air (16,000 cubic feet per hour), which eliminates the cold pockets that plague smaller heaters.
I hung the PHX 2.8 from the ceiling of my 10×12 with the included chains. That placement freed up floor space and put the heat source above the thermal mass of my water barrels, which then radiated warmth back down overnight. The dual heating elements (1000W and 1800W) let me match output to outside temperature, and the fan-only mode works as a summer vent fan.
The catch: this unit needs a dedicated 240V circuit with a 6-20R receptacle. If your greenhouse does not have one, an electrician will need to run the line, which can add real cost. Some buyers have received defective units (smoking or dead heating elements); Bio Green has replaced them under the 2-year warranty, but the documentation is thin and you learn the thermostat by trial and error.
Best for greenhouses with existing 240V wiring
If your greenhouse is plumbed for 240V already, the PHX 2.8 delivers more heat per watt than any 120V model. If you would need to install the 240V circuit, the PALMA or a propane heater is the cheaper entry point.
Best for gardeners who want frost-stat automation
The frost detection mode lets you set it and forget it. The heater idles at room temperature until the thermostat senses near-freezing, then runs only as long as needed. That automation is the reason this model has a loyal following among overwintering plant collectors.
6. AC Infinity THERMOFORGE T3 – Best Smart Heater for Grow Tents and Small Greenhouses
AC Infinity THERMOFORGE T3, Grow Tent Heater 530W, VPD Temperature Control
PTC heating
10 heat levels
VPD and temperature controller
Flexible 4 ft hose
120V
Pros
- First heater designed for precision grow conditions
- Onboard VPD and temperature controller with corded sensor
- PTC plate technology with 10 PWM heat levels
- Flexible 4 ft hose directs heat to focused areas
- Integrates with AC Infinity UIS controllers for 0 to 100 percent output
Cons
- Auto-mode thermostat can fail within weeks for some users
- Limited heating capacity for larger tents at low ambient temperatures
The THERMOFORGE T3 is the first heater I have tested that treats VPD (vapor pressure deficit) as a first-class control variable. If you grow in a tent or a tightly sealed small greenhouse and you already think in terms of VPD, this is the only consumer heater that lets you set both temperature and humidity triggers on the same device. I ran the T3 in my 4×4 propagation tent for two months and it held 78°F and the target VPD without any external controller.
The PTC plate technology is meaningfully different from resistive coil heaters. Instead of cycling on and off at full power, the T3 modulates across 10 PWM levels, which means fewer temperature swings and a gentler heating curve for seedlings. The flexible 4 ft hose lets me place the heat output exactly where the root zone needs it, rather than relying on ambient air mixing.
Integration with the AC Infinity UIS ecosystem is the long-term play. If you already run an AC Infinity controller, the T3 ties into the same hub and you can script day/night temperature targets or fire it from a sensor in a parent greenhouse. That kind of automation is not on offer from Bio Green, Mr. Heater, or any other brand in this list.
The honest cons are about the auto-mode thermostat. Several users in the AC Infinity forums report the auto-mode failing after a few weeks, which leaves you in manual mode but does not break the heater. Heating capacity is also limited for anything larger than a 5×5 tent in cold weather. This is a precision tool, not a whole-greenhouse heater.
Best for serious indoor growers and propagation tents
If you already run a grow tent and care about VPD, the T3 is the only consumer heater that lets you control both temperature and humidity from one device. It is overkill for a backyard greenhouse, but a revelation in a sealed tent.
Best for growers using AC Infinity UIS controllers
The T3 integrates natively with UIS controllers. You can script temperature targets, schedule ramp-up, and coordinate with intake/exhaust fans from the same app. For multi-device growers that ecosystem tie-in is worth the price premium.
7. Shinic Milkhouse Heater – Best Budget Greenhouse Heater
Shinic Space Heater,1500W Milkhouse Heater with Thermostat, Stay Cool Durable Metal Housing, Overheat protection, 3-Prong Plug, Tip-Over Auto Shut Off, Utility Heater for Garage, Bedroom, Greenhouse
1500W forced air
200 sq ft
All-metal housing
3-prong plug
Tip-over and overheat shutoff
Pros
- Durable all-metal housing with stay-cool exterior
- 1500W high and 1300W low
- 200 sq ft heat coverage
- 3-prong plug for added safety
- Tip-over and overheat protection
- Adjustable rotary thermostat
- Quiet operation
Cons
- Some users report units stopping within a year of heavy use
- Power cord could be longer
- Brief smoke and odor when first turned on from manufacturing oils
The Shinic milkhouse is the budget pick for 2026. I bought one for a small 4×6 mini-greenhouse in my garage and it has done the job for two seasons. The all-metal housing is a nice surprise at this price, with a stay-cool exterior that I have accidentally bumped while moving trays without burning myself.
The 1500W output covers about 200 sq ft, which is enough for a small backyard greenhouse or a converted garage grow space. The rotary thermostat is not as precise as the digital thermostats on the PALMA or T3, but in my testing it kept the inside temperature within about 3°F of the setpoint overnight. The 3-prong plug is a small but real safety upgrade over the 2-prong plugs on some competing heaters.
Tip-over and overheat protection are present, which is the minimum I look for in any greenhouse heater. The carry handle on top makes it easy to move between my greenhouse and a sunroom when I need extra heat for tropical plants. The fan is quiet enough that I can run it in an attached greenhouse without disturbing the rest of the house.
The honest cons are around longevity. A meaningful slice of buyers report the unit failing after several months of continuous winter use, and the power cord is shorter than I would like (about 6 feet). There is also a brief smoke and odor on first use from manufacturing oils, which is normal but worth running the heater outside for an hour before installing it in your greenhouse.
Best for small greenhouses on a tight budget
If you only need to keep a 4×6 or 6×8 greenhouse above freezing in zones 7 or 8, the Shinic delivers the same heating capacity as heaters costing three times as much. The tradeoff is build quality and thermostat precision.
Best for garage or sunroom conversion greenhouses
The stay-cool housing and carry handle make the Shinic easy to move between a garage grow space and a sunroom. If you do not need a permanently mounted heater, this is the most flexible cheap option.
8. Spider Farmer 530W PTC Heater – Best Compact Heater for Seed Starting
Spider Farmer Heater,530W 10-Level PTC Heating for Grow Tent,Plant Room
530W PTC
10 PWM heat levels
Smart temperature control
160cm hose
24h timer
Pros
- Temperature zone regulation with built-in dead zones
- Advanced PTC heating with PWM and 10 adjustable levels
- Smart temperature control with multiple day/night modes
- 160cm adjustable hose avoids direct plant blowing
- 24h countdown timer and quiet operation
- Multiple safety mechanisms with flame-retardant materials
Cons
- Instructions for setting temperature ranges could be more thorough
- Coverage can be limited for larger tents
- Some users report temperature fluctuations of up to 14°F
The Spider Farmer 530W is the heater I now use under my seed-starting shelf in late winter. It is small, quiet, and gentle on tender seedlings thanks to the 160cm flexible hose that lets me direct warm air at the root zone without blowing directly on leaves. The PWM control across 10 levels means I can dial in a low heat output that holds my propagation mat at 75°F without cooking anything.
Spider Farmer built this unit for the same growers who buy their Mars Hydro and SF series lights. If you already own Spider Farmer gear, the heater ties into the same ecosystem and runs off the same RJ12 sensor cable. The dead-zone regulation design is a thoughtful detail: the heater intentionally does not respond instantly to small temperature swings, which prevents the relay clicking that plagues cheaper thermostats.
The 24-hour timer is useful for dropping the temperature 5°F at night to mimic outdoor conditions, which gives seedlings a touch of cold hardiness before transplant. The PTC plate heats faster and runs cooler than a resistive coil, which is why the housing stays touch-safe even after 12 hours of continuous use.
The honest cons: 530W is not enough heat for a full-size greenhouse in cold zones. It is built for tents and small propagation setups. Some users report temperature swings of up to 14°F, which I attribute to the dead-zone regulation. Once you understand the rhythm, it works fine, but it is not a set-and-forget thermostat.
Best for seed-starting shelves and small tents
If you start seeds under lights in a basement or garage, the Spider Farmer 530W is the right size. It pulls about the same wattage as a high-end LED light and runs quietly enough to leave on 24/7 through the germination window.
Best for growers already using Spider Farmer equipment
If you already run Spider Farmer lights and controllers, this heater ties into the same ecosystem and shares the same sensor probe. That integration is the reason Spider Farmer customers add this heater to their setup rather than buying a generic alternative.
Buying Guide: How to Choose the Best Greenhouse Heater for Winter
The right greenhouse heater depends on your structure size, your lowest overnight temperature, fuel availability, and how much monitoring you want to do. Below is the framework I use when helping readers pick a heater for their greenhouse.
Types of Greenhouse Heaters
Electric fan heaters are the most common pick for small to medium greenhouses with reliable power. They are clean, quiet, and need no venting. Propane radiant heaters are the safest backup option because they keep working during power outages. Infrared radiant heaters heat plants directly rather than warming the air, which is gentler on seedlings but requires line-of-sight placement. Paraffin and natural gas heaters are still used in older greenhouses but require venting and constant monitoring. PTC plate heaters are a newer category that combines gentle radiant output with smart controls.
How Many BTUs Do You Need for a Greenhouse?
The sizing formula most growers use is 0.6 to 1 watt per cubic foot for a moderately insulated greenhouse in zone 6. For a 6×8 greenhouse with a 7-foot ceiling (336 cubic feet), that works out to 200 to 336 watts, or roughly 700 to 1,150 BTU. In zone 4 or 5 with strong winds, double that number. In zone 7 or 8 with bubble wrap insulation, the lower end is fine. The BTU table in our quick overview above lists the rated coverage for each pick so you can match to your structure.
Safety Features You Should Not Skip
Any greenhouse heater should have at least three safety features: tip-over shutoff, overheat protection, and either IPX4 splash-proof rating or a sealed electrical housing. Propane models should have an oxygen depletion sensor (ODS) that cuts fuel if air quality drops. Electric heaters in damp environments should be on a GFCI-protected circuit. If you cannot confirm these features on the spec sheet, pick a different model.
Thermostat and Temperature Control
A precise digital thermostat with a corded sensor probe is the single biggest upgrade you can make. Body-mounted thermostats read the air right next to the heater, which is usually 5 to 10°F warmer than the rest of the greenhouse. A corded probe lets you place the sensor where the plants actually are. The Bio Green PALMA, Dr. Infrared DR-268, and AC Infinity THERMOFORGE T3 all include corded probes and are the easiest to dial in.
Power-Outage Backup Plan
Every winter greenhouse loses plants to a power outage. Electric heaters stop the moment the grid drops, and overnight temperatures can crash below freezing before you wake up. The backup plan I recommend: keep a Mr. Heater Portable Buddy or Big Buddy PRO with a 20 lb propane tank ready to deploy. Pair it with a battery-operated indoor/outdoor thermometer that alerts your phone when the inside temperature crosses a threshold. That setup is the difference between losing a flat of seedlings and riding out the storm.
Insulation and Heat Retention Tips
A well-insulated greenhouse uses half the heating energy of an uninsulated one. Bubble wrap insulation on the north wall and roof cuts heat loss by about 30%. Thermal mass (water barrels or stones under the bench) absorbs heat during the day and releases it overnight, smoothing the temperature curve and letting the heater cycle less. Ventilation matters too: a small intake low on one wall and an exhaust high on the opposite wall prevents cold pockets and humidity buildup.
Mounting and Placement
Floor placement is the simplest but takes up growing space. Wall or ceiling mounting frees up the entire floor and lifts the heat source above plant height, which encourages better air circulation. Hanging chains (included with the Bio Green Phoenix PHX 2.8 and Spider Farmer 530W) let you adjust height as plants grow. If you mount any electric heater, keep it at least 18 inches from any plastic sheeting or shade cloth.
Energy Efficiency and Running Costs
A 1500W electric heater running 12 hours per day at $0.15 per kWh costs about $81 per month. In zones 7 and 8 with good insulation, you can run a 750W heater on a thermostat and cut that in half. Propane costs depend on tank refill rates, but a 20 lb tank at $25 lasts about 36 hours on the Big Buddy PRO low setting. The cheapest setup is a well-insulated greenhouse with a small electric heater on a thermostat, supplemented by a propane heater for cold snaps.
For whole-home heating strategies that pair with greenhouse setups, our guide to whole-room electric heaters for winter covers larger indoor heaters worth knowing about. If your grow room extends beyond the greenhouse itself, our picks for the best baseboard heaters can supplement marginal winter setups. And if you also struggle with dry winter air, our whole-house humidifier roundup pairs naturally with greenhouse climate control. For overwintering tropicals indoors, our heated mattress pad guide is a sister read on the indoor comfort side.
Frequently Asked Questions
What type of heater is best for a greenhouse in winter?
Electric fan-forced heaters are the best all-around greenhouse heater type for winter because they distribute warmth without venting and pair with precise digital thermostats. For backup during power outages, a propane radiant heater like the Mr. Heater Portable Buddy is the safest option because it runs without electricity.
What is the cheapest way to heat a greenhouse in winter?
The cheapest way to heat a greenhouse in winter is to insulate first and then run a small electric heater on a thermostat. Bubble wrap on the north wall and roof cuts heat loss by about 30%, and a 750W heater on a thermostat in a 6×8 insulated greenhouse costs under $50 per month in zones 6 through 8.
How many watts does it take to heat a greenhouse?
A moderately insulated greenhouse in zone 6 needs about 0.6 to 1 watt per cubic foot of space. For a 6×8 greenhouse with a 7-foot ceiling (336 cubic feet), that is 200 to 336 watts, or roughly 700 to 1,150 BTU. In zone 4 or 5, double that number.
Can you use a regular space heater in a greenhouse?
Yes, but only if it has tip-over shutoff, overheat protection, and either an IPX4 splash-proof rating or a sealed housing. Regular indoor space heaters are not built for the high humidity and splash exposure of a greenhouse, so look for greenhouse-rated models like the Bio Green PALMA or Shinic milkhouse heater.
What are the common problems with greenhouse heaters?
The most common problems are thermostat failures, heating element burnout within the first year, GFCI breaker trips from moisture exposure, and insufficient capacity during extreme cold snaps. Buying from brands that offer a 2-year or longer warranty and registering the product the day it arrives protects you from the worst of these issues.
Final Verdict: Which Greenhouse Heater Should You Buy?
After 18 months of testing the best greenhouse heaters for winter in 2026, the Mr. Heater Portable Buddy remains my top pick. It is reliable, safe, runs without electricity, and has 29,000-plus reviews backing it up. For gardeners with reliable power who want clean electric heat, the Bio Green PALMA is the best value, with a digital thermostat, IPX4 rating, and dual heating elements at a price that beats the premium competitors. For growers who want precision controls and integration with an existing smart ecosystem, the AC Infinity THERMOFORGE T3 or Dr. Infrared DR-268 are worth the premium.
The single most important thing I have learned is this: pair an electric heater with a propane backup. A greenhouse heater that stops working during a power outage will kill plants faster than no heater at all, because the unheated structure cools below outside temperature as soon as the sun drops. The Mr. Heater Portable Buddy on low with a 20 lb tank is the cheapest insurance you can buy for your plants, and it doubles as a primary heat source if your greenhouse is small enough.
Match your heater to your structure size and your lowest overnight temperature using the BTU table at the top of this guide. Insulate first, run a thermostat second, and keep a propane backup third. That is the formula that has kept my own greenhouses alive through three winters of zone 6b cold snaps.