What Is A Paraffin Greenhouse Heater? (Heating Output Specs)
A paraffin greenhouse heater burns an approved kerosene-type fuel to warm a greenhouse. Its useful heat output is model-specific, and the right size depends on heat loss, not floor area alone. Check the heater’s rated output, fuel use and flue requirements, then match them to the greenhouse, local conditions and safe installation rules.
I have seen how one unfamiliar number in a heater manual can make a simple choice feel harder than it is. A rating in kilowatts tells you about heat, while a fuel-use figure tells you how quickly the heater may use fuel. They are related, but they are not the same thing.
What Is a Paraffin Greenhouse Heater?
A paraffin greenhouse heater burns liquid fuel to produce heat. In many places, “paraffin” means kerosene, but the exact approved fuel depends on the heater. These heaters may be flued or unflued, so check the model’s instructions before choosing or using one.
A flued model sends combustion products outside through a flue. An unflued model releases them into the greenhouse. Burning fuel also creates water vapour, and poor combustion can create carbon monoxide (CO), a poisonous gas. A heater’s label and manual should identify its fuel, output and installation requirements.
“Greenhouse-rated” matters: the appliance and its instructions should suit the intended setting. Do not assume a heater designed for another use is suitable for a greenhouse. Nor should you treat “paraffin,” “kerosene” or another fuel name as proof that a particular grade is approved. Check the manual.
How to Read Heater Output and Fuel Specs
A heater’s output rating describes its heating capacity, usually in kilowatts (kW). One kilowatt is 1,000 watts. Fuel consumption, often shown in litres per hour (L/h), estimates how fast the unit uses fuel under stated conditions. Check whether a specification refers to heat input or useful heat output.
Fuel contains energy, but not all of it becomes useful heat in the greenhouse. Kerosene contains roughly 9.8–10 kilowatt-hours of fuel energy per litre. Actual delivered heat and fuel use depend on the heater’s design, operating level and cycle, so use the maker’s figures for planning.
| Figure | What it tells you | What it does not tell you |
|---|---|---|
| Rated output, kW | The heater’s stated heat capacity | Whether it will meet your greenhouse’s heat loss |
| Fuel consumption, L/h | Fuel use under the maker’s stated conditions | A guaranteed rate in every use pattern |
| Tank capacity, L | The amount the tank holds | Exact run time in changing conditions |
| Fuel energy, kWh/L | Approximate energy stored in the fuel | Useful heat delivered by a particular heater |
For example, a 2.5 kW heater running near full output would use about 0.25 L/h if fuel energy were converted to heat at 100% efficiency: 2.5 kW divided by about 10 kWh/L. This is a simplified estimate, not a product specification or a runtime promise. Use the manufacturer’s rated consumption when comparing heaters or estimating refill needs.
Heater Selection, Greenhouse Sizing & Safety Setup
Choose a flued, greenhouse-rated heater by estimating the structure’s heat loss, then checking the heater’s approved fuel, output and installation instructions. Floor area alone is not enough: glazing, frame, gaps, weather and the temperature you want all affect the required heat.
A basic estimate is:
Heat demand (W) ≈ U × A × ΔT
Here, U is the overall heat-loss coefficient in watts per square metre per degree (W/m²·K), A is the area of the greenhouse envelope in square metres, and ΔT is the difference between target indoor and outdoor temperatures in kelvins or degrees Celsius. Envelope area means the walls and roof that lose heat, not just the floor.
This estimate does not capture every effect. Air leaking through gaps adds heat demand, as can door opening and other site conditions. Ask the greenhouse or heater supplier for appropriate values where available. Treat a simple calculation as a starting point, not a guarantee.
Worked greenhouse sizing examples
These are illustrative calculations, not measured installations or universal sizing advice. The U-values and envelope areas below are assumptions chosen to show how the method works. Use values that fit your structure and local conditions.
| Illustrative scenario | Assumed envelope area | Assumed U-value | Temperature difference | Basic heat-loss estimate |
|---|---|---|---|---|
| Small, sheltered greenhouse | 20 m² | 6 W/m²·K | 15 K | 1,800 W (1.8 kW) |
| Larger greenhouse in colder conditions | 40 m² | 6 W/m²·K | 20 K | 4,800 W (4.8 kW) |
The first estimate is 6 × 20 × 15 = 1,800 W. The second is 6 × 40 × 20 = 4,800 W. Both exclude extra demand from air leakage and controls. A heater’s rated output should be compared with the estimated demand, but the manufacturer or a qualified installer can help account for the structure and local requirements.
Check the installation before buying
Confirm the following details before selecting a model:
- The heater is intended and rated for greenhouse use.
- The manual approves the exact fuel grade you plan to use.
- Its rated output and fuel consumption are clear.
- The flue type, route and installation requirements suit the site.
- The required clearances and base are achievable.
- Local fire and building rules are met.
There is no single clearance or ventilation rate that applies to every heater and greenhouse. Follow the appliance label and manual, along with local rules. Place the heater on a stable, non-combustible base and protect it from water, plants and accidental contact. Use a suitable CO alarm where required; an alarm does not replace a correctly installed flue.
Starting, Temperature Control & Greenhouse Operation
Safe operation begins with the maker’s cold-start instructions and a quick condition check. Confirm that the heater, fuel system and flue are sound before lighting it. Once running, watch for stable operation, track the temperature and fuel use, and follow the manual’s limits.
Before filling or starting, check the tank, cap, wick or burner, seals, flue and guards for damage or leaks. Fill only when the heater is cool and off, using approved fuel. Clean up any spill before ignition.
Use the manufacturer’s start-up steps. Confirm that ignition is stable and the exhaust path is clear. Keep required ventilation, and do not leave the heater unattended unless the manufacturer explicitly says it is designed and approved for unattended operation. Follow the instructions for temperature controls; do not assume every model has a thermostat or automatic shutoff.
Stop using the heater if you notice fumes, soot, an abnormal flame, a damaged or blocked flue, or a CO alarm. Leave the area, ventilate it if you can do so safely, and have the appliance and flue checked before using them again. If anyone may have CO poisoning, get outside and contact emergency services.
Inspection, Cleaning & Burner or Wick Maintenance
Routine inspection helps you spot faults before they become a bigger problem. Follow the maker’s service schedule and cleaning instructions, since burner and wick designs differ. Never change an adjustment or dismantle a part unless the manual says how to do it safely.
With the heater off and fully cool, check for fuel leaks, soot, damage and loose or blocked flue parts. Inspect the wick or burner for deposits as the manufacturer directs. Soot or a change in flame can signal a problem; stop use and seek service rather than trying to correct an unknown fault by guesswork.
Keep guards in place and keep the exhaust route unobstructed. If a part needs replacement, use the specified part or an approved service provider. A clean appearance does not prove that combustion is safe, and a CO alarm is not a substitute for maintenance.
Shutdown, Off-Season Storage & Fuel Care
Use the maker’s shutdown method, then let the heater cool fully before inspection or storage. Store fuel only as the product label and local rules allow. Keeping the appliance and fuel in good condition helps reduce leaks, spills and trouble at the next start.
After shutdown, check for soot, deposits, leaks and flue blockage when the unit is cool. Clean and service it at the intervals in the manual. For off-season storage, follow the maker’s directions for the tank, wick or burner, and protect the heater from damage.
Do not leave fuel in a heater for storage unless its instructions allow it. Keep fuel in an approved container, away from ignition sources, and follow its label and local storage rules. Before the next season, inspect the heater and flue again; do not use a damaged or obstructed appliance.
Frequently Asked Questions
Is paraffin the same as kerosene?
In common usage, paraffin often means kerosene, especially in some regions. Names and fuel grades can vary, though. Check the heater manual for the exact approved fuel and grade. Do not assume that every product sold as kerosene or paraffin will work safely in every heater.
How many kilowatts do I need for my greenhouse?
There is no single output that suits every greenhouse. Estimate heat loss using U × A × ΔT, then account for air leakage and controls. Compare the result with the heater’s stated useful output, and seek advice if the structure’s heat-loss values are unknown.
How much fuel does a 2.5 kW heater use?
A simplified energy calculation gives about 0.25 L/h near full output: 2.5 kW divided by roughly 10 kWh of fuel energy per litre. This assumes ideal conversion and is not a guaranteed consumption rate. Use the heater maker’s rated L/h figure for planning.
Is a flued heater safer than an unflued one?
A flued heater sends combustion products outdoors, while an unflued model releases them inside. A flue can still be unsafe if it is blocked, disconnected or installed incorrectly. Follow the heater instructions and local rules; do not treat a flue as a reason to skip inspection.
Can I use any kerosene or paraffin fuel?
No. Use only the fuel grade approved in the heater manual. Fuel products can differ, and a name alone does not confirm compatibility. If the manual is missing or unclear, ask the manufacturer or a qualified supplier before filling the heater.
Does a paraffin heater add moisture to a greenhouse?
Burning fuel creates water vapour. An unflued heater releases combustion products, including that vapour, into the greenhouse; a flued model sends exhaust outdoors when correctly installed. The amount depends on the heater and its operation, so check the manual for product-specific details.
What should I do if I smell fumes or see soot?
Stop using the heater, leave the area and ventilate it if you can do so safely. If a CO alarm sounds or anyone feels unwell, get outside and contact emergency services. Do not restart the heater until the appliance and flue have been checked.
Can a greenhouse paraffin heater run unattended?
Only if the manufacturer explicitly designs and approves that model for unattended operation. Do not infer this from a timer, thermostat or other feature. Follow the manual’s supervision instructions, and keep required ventilation and safety checks in place during operation.
(This article was written by one of our staff writers, Evan Bradley. Visit our Meet the Team page.)
