A picture of a waste oil heater or waste oil burner heater from Flexiheat UK for warm air heatingFlexiheat UK

Waste Oil Heater /Multi Oil Fired Heater – Automatic Ignition -Output range- 23 kW to 180 kW

A picture of a waste oil heater or waste oil burner heater from Flexiheat UK for warm air heating

Waste Oil Heater – Automatic Ignition – Kroll

Waste Oil Heater – Our waste oil warm air heaters are the ideal solution for heating and controlled ventilation of small, medium and large areas such as workshops, car and lorry garages, industrial buildings, warehouses etc. A waste oil heater is the best way to get free heat! Recycle your waste oil, and burn waste oil with our range of waste oil heaters.

The operating principle is simple, reliable and extremely effective: cold air sucked by the fan is conveyed towards the heat exchanger, warmed up by the combustion that develops inside it; when crossing, the air raises its temperature and then it is distributed in the area to be heated. The heaters also allow the ventilation of the environment during the summer season. The peculiarity of the “dry” heating technology is to directly and immediately transfer the heat produced by combustion in the environment to be heated, without use of intermediate heat transfer fluids (each intermediate heat exchange involves thermal losses and further system complexity), ensuring a high overall efficiency of the system, combined with a very low thermal inertia. These distinctive features make the installation of our waste oil cabinet warm air heaters particularly advantageous in cases where rapid, reliable, intermittent or occasional heating is required or where there is a risk of freezing. Flexiheat cabinet warm air waste oil space heaters require very little maintenance and ensure durability and reliability over time.

waste oil heater

Our cabinet warm air heaters have a wide range of energy-efficient models that meet the efficiency and atmospheric emissions requirements of the new European ERP2018 legislation which came into force on 1 January 2018.

Multi Fuel Capability of our Multi Oil Heater / Waste Oil Heater 

  • Non waste fuel such as 35 or 28 second Heating Oil/Diesel Oil
  • Processed Fuel Oil ( PFO )
  • Rapeseed Oil
  • Linseed Oil
  • Vegetable Oils 
  • Used Engine Oil (subject to licensing control- please see here for more information on this subject)  
  • Hydraulic Oil
  • Bio Diesel

Please note that solvents, thinners, transformer oil, petrol, and petrochemical-based oils should never be used as a fuel in these waste oil burners. They are designed to burn waste oil not waste fluids!

Waste oil from gearboxes, hydraulic systems or transmissions (gearbox oil) burn really well.

Burning waste oil is subject to environmental permitting regulations / the industrial emissions directive.

Our Energy range of Waste Oil Heaters which are warm air heaters , ensure maximum energy efficiency and environmental comfort thanks to the ability to condense at a reduced thermal load.

  • 8 models with a thermal capacity from 23 kW to 180 kW and air flow from 1,650 to 13,800 m3 / h.
  • Suitable for direct diffusion with an air outlet plenum, or as a ducted waste oil heater.
  • High efficiency ~ 91 %.
  • Heat exchanger made entirely of stainless steel AISI 304 with aerodynamic profile and turbulent imprints.
  • Combustion chamber in AISI 430 stainless steel, ensuring long service life
  • High performance centrifugal fans with variable ratio transmission (adjustable during installation)

The vast majority of these waste oil space heaters are supplied with the standard free blowing head configuration , that allows you to direct the warm air via the grills to the required area. We also offer the units suitable for ducted systems, with high pressure versions up to 800 Pa available. The standard version is designed to treat air with a minimum temperature of -15 ° C. On request, suitable versions are available for operation with intake air down to -25 ° C and -40 ° C.

With any warm air heating system, we recommend also installing destratification fans, which push the warm air that rises withing the building back down to ground level. Destrat fans can save up to 20% to 30% on the energy consumption, reducing the running costs of your heating system.

Waste Oil Heater Construction

• External casing consists of demount-able panels made of pre-painted galvanized steel sheet, with thermal insulation of the surfaces exposed to the heat exchanger. For all the models there is a load-bearing structure of painted galvanized steel of particular profile, joined by special die-cast aluminium joints.
• High efficiency heat exchanger, made of welded sheet steel, easy to inspect for normal operations of cleaning and maintenance, consisting of:
– Flame inversion combustion chamber, in AISI 430 stainless steel resistant to high temperatures, of large volume and low thermal load, with circular or ellipsoidal profile, complete with inlet with burner plate and flame control spy.
– Heat exchanger tubes entirely in AISI 304 stainless steel, suitable for the heater operation with reduced thermal power in condensation. Fumes tubes have a flattened tubular section with staggered and opposing turbulent imprints, with special reticular turbulators for maximum efficiency, complete with front and rear manifold with detachable inspection door, entrance for chimney connection and connection for condensation drainage.
• Ventilation group consists of one or more high performance centrifugal fans with low level of sound emission, powered by an electric motor (s) connected by a pulley and belt drive system, with a variable ratio driven pulley.
• Fan-limit safety thermostat/s, for automatic control of ventilation group and for the safety stop of the waste oil burner in case of abnormal overheating of the air.
• Electrical panel for command and control with general switch.

Waste oil heater range technical data –

Waste oil warm air heater range technical data 25kW to 180kW from Flexiheat UK

Download the Flexiheat Waste or Multi Oil Warm Air Heaters SZ Brochure from Flexiheat UK

Waste Oil Heaters – Burner Options 

All of our waste oil heaters, withing this range require a compressed air supply to operate the waste oil burner attached to the heater cabinet.

We use two burner options on these waste oil warm air heaters – depending on the kW output required of the heaters

The first is the Germany Burner –  as pictured below – This can be fitted up to the 160.3 kW Output heater, the benefit of this multi oil burner is that not only can you supply your own compressed air to the unit , but we can also supply what is classed as a quiet compressor ( 70dBA max , for reference normal speech is 60dBA) – which is powered and controlled by the burner on demand. This results in lower running costs, as the energy needed is reduced, as you don’t have to run your system compressor all day and night.Our quiet compressors are the diaphragm type ( Oil Free )and are continuously rated, which is very important as many compressors aren’t, requiring very little maintenance. The quiet compressor is also very small  , about the same size as a brief case , and this sits next to, or underneath the burner taking up very little space. Should you wish to utilize your own compressed air supply, this isn’t a problem , the 20 to 100 kW multi oil burners require on 1 Bar supply, and the 100 kW and 150 kW require 1.4 Bar supply. We do insist that you install a good quality quality water and air filter prior to the burner though.

We offer this quiet compressor for the burners matched to these multi oil heaters , but should you wish to supply the compressed air requirements from your own compressor, again the pressure requirement is not large, only 1.5 Bar for this range of burners fitted to our waste oil heaters, and a flow requirement of 120 Litres/ minute and again we insist that you install a good quality water and air filter prior to the burner.

Waste Oil Heaters – What you need to know 

  1. When burning correctly, these units burn as clean as a standard oil heater, with no plumes of black smoke etc
  2. The burner attached to the waste oil heater, is a multi oil burner, which means it will burn gas oil (sometimes referred to as red diesel), kerosene, waste engine oil (with some conditions – see point 3 ), transmission oil, vegetable oil, and used vegetable oils ( with some conditions – see point 4)
  3. If you are using waste engine oil, then if you have over 50% synthetic oil, and by this we mean any oil that has the word synthetic in it , to mineral oil , then you need to add 15% gas oil to the waste engine oil. This needs to be agitated, so it mixes with the engine oil (normally done, by dropping a compressed air line into tank, for approximately ½ hr after introducing the gas oil into the waste engine oil). This needs to be done on a monthly basis, as the diesel will settle to the top of waste oil over this period and needs to be remixed
  4. If you are using waste vegetable oil, then the fats have to be removed, via settling out, the oil should also be filtered down to 5 micron

Waste Oil Heater Maintenance 

“You get nothing, for nothing” as the saying goes, and if you are burning waste oil, then they are not made to a definite BS / EN , which specifies their filtration level, their calorific value etc. Waste engine oil often has small metal particles suspended in the oil, which should lie as a fine white dust if the heater is burning correctly. This builds up over a period of time, how quickly this does depends on how “dirty” the oil is (remember it’s your oil, not mine – I can’t tell you ! ) thus we recommend opening up an inspecting the warm air heater every 300 burning hours ( roughly 6 weeks in the winter ) and cleaning the combustion chamber , and the heat exchanger – this should take approximately ½ to ¾ of an hour of your time – if so required- if it isn’t dirty, close the waste oil heater back up and check again in another 6 weeks . If you are not prepared to do this, to ensure the correct operation of the boiler, please buy a standard oil or gas warm air heater off us, and don’t moan to us regarding how much your fuel bills are !!! , you get free heat via your waste oil heater, it needs you time!!

The multi oil burner is an “oil burner “not a miracle worker, and things like water,  brake fluid and clutch fluid, should not be burnt as they cause problems to the burner ( they destroy the rubber seals, that we use in our nozzles, and crystallize up, causing blockages in the nozzles and pipes of the burner – they are fluids not oils !!!!!

Also no petrol or paint thinners either!!! We use a pre-heater to heat the oil up to 80 C  for waste engine oil , or up to 140 C for vegetable oil . This will ignite the fluids and cause a fire!!!

A picture of a waste oil heater or waste oil burner heater from Flexiheat UK for warm air heating

Waste Oil Heater – Automatic Ignition – Kroll


A waste oil heater is the best way to get free heat! Recycle your waste oil with our range of Kroll waste oil heaters. We can offer a full range of Kroll waste oil heaters and waste oil heater spares. Your investment in a Kroll waste oil heater will quickly pay for itself.

  • High efficiency – Over 91%
  • Minimum service and maintenance – Our Stainless Steel Combustion Chamber ensures the best combustion with longer maintenance intervals
  • Clean, soot free combustion
  • Fast and simple installation
  • Room thermostat for economical operation (optional extra)
  • Automatic burner with pre heating
  • Can be connected to a bulk tank if required

Our stationary warm air waste oil heaters are the most economical way to heat your commercial building, warehouse or garage. Available with adjustable side vents or ducted version to get the most use of the heat produced. They can be fully automated and thermostatically controlled. All of our multi oil heaters have a stainless steel combustion chamber as standard and we often get asked why we construct our waste oil heaters this way, the answer is simple , it’s a better engineering solution as stainless steel is a superior heat conductor allowing our waste oil heaters to get warmer , faster ! as well as being able to withstand higher temperatures than standard steel, ensuring our waste oil heaters have an extremely long service life.  Our 25kW to 110Kw units also have stainless steel heat exchangers (for long product life) fitted as standard to ( this is an optional extra for our larger units). All of our waste oil heaters have –

  • An access panel to the heat exchanger – which allows easy access for cleaning the unit
  • Our waste oil burners have a swing arm – which allows easy removal of the burner from combustion chamber, making cleaning the nozzle and diffuser plate of the waste oil burner a breeze !

Waste Oil Heater – Showing Internal Configuration

Internal picture of our Kroll waste oil heaters from Flexiheat UK

Internal picture of our Kroll waste oil heaters from Flexiheat UK

Features of our Waste Oil Heater / Multi Oil Heater


The burner is equipped with a photocell that continuously monitors the flame.

In case of ignition failure or poor combustion, lack of a flame or partly blocked nozzle, the photocell stops the burner.


This multi functional thermostat ensures that the main fan only starts after the combustion chamber has been sufficiently heated. Therefore, there is no cold air blown before the heater has warmed up.


Electrical overload is protected by a trip system for both the main fan and the burner.

Heating overload is protected by a limit thermostat built into the heater control thermostat. This has an automatic reset.

Any obstruction of the main fan or its air stream is secured by a manually reset overload protection.


In summertime the heater can be used for ventilation only

Download The Kroll Multi Oil or Waste Oil “SZ” Brochure from Flexiheat UK

Multi Oil – Waste Oil Tank – 59 or 109 Litre Storage 

We highly recommend that you use our oil tanks with our multi / waste oil burners, which are fitted to our automatic waste oil warm air heaters or our multi / waste oil boiler packages.

waste oil heater day tank

waste oil heater day tank

The purpose of the day tank is two fold –

  1. It can be used as your oil tank for your fuel, negating the need for an external oil tank, depending on the size of your waste oil burner, it may need topping up every couple of days or may be every week depending on your usage.
  2. You can also use this as in intermediate oil tank , from your external oil tank and there are numerous advantages for this –
  • You have a quantity of oil, which is stored internally within the building, which should mean that the oil is warmer than the oil in the external oil tank. This helps the burner , as the oil does not have to be heated as high
  • The tank has a “floating oil suction line “(see picture), with a filter attached. This takes the cleanest oil as it floats on top of the oil
  • The oil is then pumped , and controlled by the burner , via a filter , ensuring you have the cleanest possible oil to the burner
  • It is a fully automatic operation , the burner controls the pump on demand

Coupling the 59 or 109 litre tank to a bulk external oil tank –

This is an easy thing to do –

We supply a kit, that consists of a solenoid valve, and two float switches. These are to be installed to suit site conditions i.e. where ever your incoming pipework dictates

You need to make a tapping / tank connection on one of the walls of the 100-litre oil tank, for the oil supply that will be controlled with a solenoid valve.

You also need to make one tapping below the incoming oil line, which will have the solenoid valve attached to it, this is for the “control float switch “, which opens or closes the solenoid valve – for safety, the oil solenoid valve we supply is a normally closed valve, which means that the control float switch, energies the solenoid valve when more oil is required, and cuts the power to it, when the float switch is satisfied

The second float switch, which we call the “safety or alarm float switch” needs to be positioned at the top of the tank. This float switch can activate an alarm bell (supplied by others) and also be wired to kill the electric supply to the waste oil heater or burner. It is in effect an alarm system to notify you should the solenoid valve ever fail

Waste Oil Tank Schematic

Waste Oil Heater

We believe we have the best  waste oil heater for sale on the market ,German manufactured for the Kroll Units and Italy for the Energy Condensing Waste Oil Heater range, these units are engineered to the highest standards , giving years of trouble free operation, and paying back their initial cost in a short time period.

You may call these warm air heaters  – used oil heater , waste oil workshop heaters , engine oil heaters , waste oil space heater, waste oil burning heaters, waste oil burner heater, garage waste oil heater , whatever you call them , (they should really be called a ” Universal Oil Heater “) , then we have the solution for your requirements.

Universal Oil Heater 

Please be aware  that whilst “waste oil heaters” is a market term used by many , our heaters are actually universal or multi oil heaters. They burn a variety of oils that are of much higher viscosity than fuel oils. This includes used hydraulic oils , engine oils and also vegetable oils such as rapeseed , sunflower etc. However, they also burn red diesel,  diesel , 35 second oil, and kerosene fuel oils extremely well

If you require any further assistance with our Waste Oil Heaters or any of our products, please click here to contact us via email or call us direct on 01202 822221