There are two times a site heater matters: when you are trying to keep a crew working through a cold snap, and when you need to dry a building out fast so the next trade can get on. Get it wrong and you either freeze, choke on fumes, or pump so much moisture into a room that the plaster never goes off. Get it right and the job keeps moving whatever the weather is doing outside.
Autumn creeps up quicker than anyone expects, so it is worth sorting your heating before the first proper cold week rather than fighting over the last unit in the branch. This guide covers the three fuel types tradespeople actually use – propane, diesel and electric – how to size a heater to the space, the safety points that catch people out, and the specific units worth buying in the UK right now. Prices are typical high-street figures from Screwfix, Toolstation and Amazon UK at the time of writing; always check the current price before you buy.
Quick Verdict
For most tradespeople the answer is propane. A Sealey LP69C or LP55 Space Warmer gives you 16–20kW of instant, portable heat for the price of a decent cordless drill, runs off a standard bottle, and takes the chill off a room in minutes. It is the sensible first heater for the van.
If you are heating an occupied space for days on end – a fit-out crew working in a closed shell, or drying a building without soaking it – step up to an indirect diesel heater like the Sealey ABI1000, which flues its exhaust outside and blows clean, dry warm air in. For a small enclosed room, a site office or anywhere fumes are a no-go, an electric fan heater such as the Rhino FH3 is the safe, simple choice – just respect the power supply it needs.
Propane, Diesel or Electric – Get This Right First
The fuel type dictates everything else: how portable the heater is, what it costs to run, whether it dumps moisture into your building, and where you are legally allowed to use it. Choose the fuel to suit the job, not the other way round.
Propane (LPG)
The trade default. Propane space heaters are cheap to buy, light to carry, need no cable, and throw serious heat the moment you light them. They run off a standard red propane bottle and most have piezo ignition and a safety solenoid that cuts the gas if the flame goes out. The catch: they are direct-fired, so all the combustion products – including water vapour – go straight into the room. That is fine for taking the edge off a well-ventilated space, but it is the wrong tool for drying, and you must keep a window or door cracked for ventilation and carbon monoxide safety.
Diesel and Paraffin
Diesel heaters split into two camps. Direct-fired units (like the Sealey AB1008) are cheaper and pump out huge heat, but like propane they vent everything into the space – good for a big draughty shed, bad for a sealed room. Indirect units (the ABI1000) burn the fuel in a sealed chamber and flue the exhaust outside through a duct, delivering clean, bone-dry warm air. That makes indirect diesel the professional choice for occupied fit-outs and for drying out a building, because you are adding heat without adding moisture or fumes. You pay for it – indirect heaters cost several times what a direct unit does.
Electric
Electric fan heaters produce no fumes and no moisture, so they are safe in enclosed rooms and need no ventilation. The limit is the power supply. A 13A socket gives you about 3kW maximum, which heats a small room but will not touch a large open space, and running one flat out all day is not cheap. On CDM sites you cannot plug a 240V heater into the 110V supply, so you need a 110V-rated fan heater fed from a site transformer. Electric is the right answer for site offices, welfare units and small enclosed second-fix jobs; it is the wrong answer for a cold, cavernous shell.
Sizing – How Much Heat Do You Actually Need?
Heat output is quoted in kilowatts (kW) or BTU per hour – 1kW is roughly 3,400 BTU/hr. As a rough working rule for a poorly-insulated site space, allow about 0.1kW per cubic metre you want to warm quickly. A single room of maybe 40–50m³ is comfortable on a 3kW electric or a turned-down propane unit. A large open floor or a draughty warehouse needs 15–30kW and realistically means propane or diesel.
Bigger is not automatically better. An oversized propane heater in a small closed room will cook you, waste gas and dump more moisture and combustion products than the ventilation can clear. Match the output to the space, and buy a unit with an adjustable burner (the LP69C dials from 9kW to 20kW) so one heater covers a range of jobs.
Ventilation, Carbon Monoxide and Moisture – The Bit That Bites
Every direct-fired gas or diesel heater consumes oxygen and produces carbon monoxide and water vapour. In a sealed room that is genuinely dangerous, and every winter there are avoidable incidents from heaters left running in shut-up spaces. The rules are simple and non-negotiable: never run a direct-fired heater in an unventilated room, always leave a permanent air gap, never use a propane heater to sleep near or in a caravan or welfare unit overnight, and fit a battery CO alarm where the crew is working. If the job needs heat in a sealed space, that is exactly what indirect diesel or electric are for.
Moisture matters for the finish, not just for safety. Burn a litre of propane and you release roughly a litre of water as vapour. Blast a freshly plastered or screeded room with a direct-fired heater and you can actually slow the cure and cause condensation to run down the very walls you are trying to dry. To dry a building out properly, use indirect heat (which adds none of its own moisture) and pair it with ventilation or a dehumidifier so the damp air is carried away.
At a Glance – Site Heaters Compared
The table below covers the pick of the current UK range across all three fuel types. Prices are typical and move with promotions and season – confirm before buying.
| Model | Fuel | Output | Best for | Approx. price |
| Sealey LP69C Space Warmer | Propane | 9–20kW | Portable all-round drying & heat | £120–£150 |
| Sealey LP55 Space Warmer | Propane | 16kW | Value workhorse, workshops | £150–£200 |
| Sealey ABI1000 Indirect | Diesel/Kero | ~30kW | Occupied spaces, clean dry heat | £900–£1,100 |
| Sealey AB1008 Direct | Diesel/Kero | ~30kW | Big open sheds, fast blast | £300–£380 |
| Rhino FH3 Fan Heater | Electric 230V | 2.8kW | Enclosed rooms, no fumes | £45–£60 |
| Sealey 110V Fan Heater | Electric 110V | 1.65–3kW | CDM sites off a transformer | £70–£110 |
The Best Site Heaters for 2026
Best All-Round Propane: Sealey LP69C Space Warmer
If you buy one heater, make it this. The LP69C is an adjustable 9–20kW (30,000–68,000 BTU/hr) propane space heater that will warm up to around 350m³, with piezo ignition and a safety solenoid that shuts off the gas if the flame dies. The combo version even offers a cordless 20V option so you can site it away from a mains lead. It is light, tough, and the adjustable burner means it copes with both a small workshop and a big open floor. Runs off a standard propane bottle. Around £120–£150 for the mains unit; well-ventilated spaces only.
Best Value Propane: Sealey LP55 Space Warmer
A simpler, fixed-output 16kW (54,500 BTU/hr) propane heater that heats around 275m³ and sips roughly 1.32kg of gas an hour. Same piezo ignition and safety solenoid, same tough build, a bit less flexibility than the LP69C but a proven workhorse for garages, workshops, yards and agricultural buildings. If you do not need the adjustable burner or the cordless option, this is the honest-value pick. Around £150–£200.
Best for Occupied Spaces and Drying: Sealey ABI1000 Indirect Diesel
When you need heat in a room people are working in, or you are drying a building without soaking it, indirect is the only right answer. The ABI1000 burns kerosene or diesel in a sealed combustion chamber and flues the exhaust outside, so what comes off the front is clean, dry, warm air – no fumes, no added moisture. Around 30kW of output on wheels, with a ducting option to push the heat exactly where you want it. It is a serious bit of kit at £900–£1,100, but for fit-out firms and anyone drying buildings for a living it pays for itself in dry walls and a crew that can actually work in the room.
Best Big Direct Diesel: Sealey AB1008
For a large, draughty, open space where ventilation is not an issue – a big shed, a barn, an open steel frame – a direct diesel heater gives you the most heat for the money. The AB1008 puts out around 30kW (100,000 BTU/hr) on wheels and will blast a cold shell warm in short order. It vents combustion products into the space, so it is for open and well-ventilated areas only, never a sealed room. Around £300–£380 – a fraction of the indirect price if you do not need the clean-air trick.
Best Electric Fan Heater: Rhino FH3 2.8kW
The safe, simple option for enclosed rooms, site offices and second-fix work where fumes are a no-go. The Rhino FH3 is a 2.8kW industrial fan heater in a heavy steel body with three heat settings and a built-in thermostat, so it holds a temperature rather than just running flat out. It plugs into a normal 13A socket, needs no ventilation, and adds no moisture. It will not heat a warehouse, but for a room you can close the door on it is the no-drama choice. Around £45–£60. For CDM sites, buy the 110V version to run off your transformer instead.
Running Costs – A Quick Reality Check
Propane is usually the cheapest way to buy a lot of heat quickly, which is why it dominates the trade. A 16kW unit will get through a bottle over a long working day, and swapping bottles is easy. Diesel is efficient for long, continuous running of a large space, which is where the fuel economy of an indirect unit tips the balance over weeks of use. Electric looks cheap to buy but is the most expensive per kW of heat delivered, so it makes sense for small enclosed jobs and site offices rather than heating big volumes all day. Match the fuel to the pattern of use and you will not overspend.
FAQs
Can I use a propane site heater indoors?
Only in a well-ventilated space, never in a sealed room, and never overnight where anyone is sleeping. Direct-fired propane produces carbon monoxide and water vapour. Keep a permanent air gap, fit a CO alarm, and if the room has to be sealed, use indirect diesel or electric instead.
What size heater do I need to dry out a building?
For drying, the heater type matters more than raw output. Use an indirect diesel heater, which adds heat without moisture, and pair it with ventilation or a dehumidifier to carry the damp air away. A direct-fired propane or diesel unit will fight you by adding its own moisture to the room.
Why can’t I use my normal heater on site?
Most UK commercial and construction sites run a 110V centre-tapped supply and ban 240V equipment. A standard 240V electric heater cannot be plugged into the site setup – you need a 110V-rated fan heater fed from a site transformer. Gas and diesel heaters sidestep the issue as they do not run off site power, but still follow the site’s ventilation and permit rules.
Propane or diesel for a workshop?
For a typical trade workshop or garage that is reasonably ventilated, a propane Space Warmer is cheaper, lighter and more than enough. Only step up to diesel if you are heating a very large space continuously, or to indirect diesel if the space is sealed and occupied.
The Verdict
Buy the fuel to suit the job. For the van and most day-to-day trade heating, a propane Sealey LP69C or LP55 is the sensible, affordable workhorse – fast heat, no cable, standard bottle. For drying a building or heating a room people are working in, an indirect diesel heater like the ABI1000 earns its higher price by giving you clean, dry warmth. And for small enclosed rooms and site offices, a Rhino FH3 electric fan heater is the safe, simple pick – just remember the 110V version for CDM sites. Sort it before the cold sets in, respect the ventilation rules, and the weather stops being the thing that decides whether the job moves.
