Quick verdict
For most UK sites, a propane cabinet heater like the Sealey LP69C is still the fastest, cheapest way to get useful heat into a shell or unheated building. If people are working in the space while it dries — plasterers, decorators, anyone breathing the air all day — step up to an indirect diesel heater like the ABI1000 instead, since it doesn’t put combustion fumes into the room. Electric only makes sense once you’ve got mains or a generator big enough to run it properly.
Propane, Diesel or Electric – Get This Right First
Propane (LPG)
Cheap to buy, cheap to run, and available everywhere — every builders’ merchant sells 19kg and 47kg bottles. Direct-fired, so it puts moisture and combustion gas into the room, which is exactly what you want when you’re trying to dry out plaster or screed fast, and exactly what you don’t want if people are working in there for hours.
Diesel and Paraffin
Direct diesel heaters are the brute-force option for big open sheds and unheated shells — huge output for the money, but noisy and fumey. Indirect diesel heaters route the exhaust outside through ducting, so the heated air stays clean, which is why they’re the standard choice for occupied spaces and drying work where air quality matters.
Electric
Clean, quiet and fume-free, but you need the power to run it — a 3kW fan heater on a domestic 13A socket is fine, anything bigger needs a 110V site supply or a generator. Best suited to smaller enclosed rooms rather than trying to heat an entire shell.
Sizing – How Much Heat Do You Actually Need?
As a rough rule of thumb, budget around 100W per square metre for a reasonably insulated space, and roughly double that for an open shell with no insulation or glazing yet fitted. It’s almost always better to slightly oversize than undersize — a heater that’s too small will run constantly and still lose the fight against an open doorway.
Ventilation, Carbon Monoxide and Moisture – The Bit That Bites
Any direct-fired propane or diesel heater needs ventilation — a cracked window or door, never a fully sealed room. Fit a CO alarm any time you’re running a direct-fired heater in an enclosed space, and be aware that both propane and diesel direct heaters add significant moisture to the air, which can undo drying work rather than help it. If drying is the actual goal, pair a heater with a dehumidifier rather than relying on heat alone.
At a Glance – Site Heaters Compared
Model | Fuel | Output | Best for | Approx. price |
Sealey LP69C Space Warmer | Propane | 9–20kW | Portable all-round drying & heat | ≈£75–£90 |
Sealey LP55 Space Warmer | Propane | 16kW | Value workhorse, workshops | ≈£55–£65 |
Sealey ABI1000 Indirect | Diesel/Kerosene | ~29kW, ducted | Occupied spaces, clean dry heat | ≈£450–£520 |
Sealey AB1008 | Diesel/Kerosene | ~29kW (100k BTU) | Big open sheds, fast blast | ≈£230–£270 |
Rhino FH3 | Electric | 2.8kW | Enclosed rooms, no fumes | ≈£45–£55 |
The Best Site Heaters for 2026
Sealey LP69C Space Warmer — Best All-Round Propane
The LP69C is the heater most builders reach for first: a portable 9–20kW cabinet that runs off a standard propane bottle, heats up almost instantly, and is light enough to move between rooms as work progresses. It’s the sensible default for general site heat and fast drying where you’re not worried about people breathing the exhaust all day.
Sealey LP55 Space Warmer — Best Value Propane
A step down in output from the LP69C but a step down in price too, the LP55 is the pick for smaller workshops or single rooms where you don’t need the bigger unit’s full 20kW. It’s the same simple, reliable cabinet design, just sized for a smaller job.
Sealey ABI1000 Indirect Diesel — Best for Occupied Spaces and Drying
Because the ABI1000 ducts its exhaust outside, it’s the right call whenever people are actually working in the space being heated — plastered rooms being dried out with trades still in there, occupied refurbishments, anywhere air quality matters. It costs several times more than a direct propane cabinet, but it’s the only sensible option once occupied working hours come into play.
Sealey AB1008 — Best Big Direct Diesel
For heating large open sheds, unfinished barns or big unheated shells fast, the AB1008 is a brute-force direct diesel heater that pushes out serious heat for the money. It’s not for occupied spaces — the exhaust goes straight into the room — but for warming a big empty space before trades move in, nothing here beats it for output per pound.
Rhino FH3 2.8kW — Best Electric Fan Heater
Where fumes genuinely can’t be an option — a small occupied room, somewhere with poor ventilation, or a space where a client is present — the Rhino FH3 is a solid, no-nonsense 2.8kW electric fan heater. It needs a proper supply to run well, but it’s clean, quiet, and simple.
Running Costs – A Quick Reality Check
Propane is the cheapest heat per kW on paper but burns through a 19kg bottle faster than people expect on a big direct heater running flat out. Diesel indirect heaters cost more upfront but are efficient to run over a long drying job. Electric is cheap to run in short bursts but becomes expensive fast on a big space if you’re paying domestic electricity rates rather than running off a generator already on site.
FAQs
Can I run a propane heater indoors overnight?
Not unattended — always ventilate the space and never leave a direct-fired heater running unsupervised overnight in an enclosed building.
Do I need a CO alarm with a diesel heater?
Yes, for any direct-fired diesel or propane heater running in an enclosed space. Indirect heaters like the ABI1000 carry lower risk since the exhaust is ducted outside, but a CO alarm is still cheap insurance.
Will a heater dry out a room on its own?
Heat alone moves moisture into the air rather than removing it — pair a heater with a dehumidifier if the actual goal is drying plaster, screed or a flood-damaged room.
The Verdict
Sealey’s propane cabinets remain the easiest, cheapest way to get heat onto most UK sites, the ABI1000 is worth the extra spend the moment people are working in the space, the AB1008 is the one to reach for on big empty sheds, and the Rhino FH3 covers you anywhere fumes simply aren’t an option.
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