Multi / Waste Oil Heater – Manual Ignition- Drip Waste Oil Heater

Waste oil workshop heaters – Output range 20kW/ 68,240 BTU’s to 55kW / 187,660 BTU’s

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Kroll W401 Waste Oil Heater from Flexiheat UK

Small waste oil heater – Experience gained over many decades makes the Kroll multi/waste oil heater a reliable, cost effective and an environmentally friendly heating product.Our W401 heater is a manual ignition, or vaporising waste oil heater- which are lower cost, simple to use and maintain and very robust.It is a vaporising heater which means it is drip fed so it does not require a compressed air supply to work unlike our larger waste oil heater, which are detailed on this page 

Unfortunately the Kroll W401 manually fired waste oil workshop heater is no longer manufactured, spare parts are still available for the unit for the foreseeable future, this unit is now superseded by either the Flexiheat”FH” range of multi or universal oil heaters or the Kozy, a waste oil workshop and garage heater that in reality in a multi fuel warm air heater, as it will also burn solid fuels to. All the details of the Kroll W401 heater have been moved to the bottom of this web page, where we still have all the technical data, and also the manuals, spare parts drawings/ list and the wiring diagram available as a downloads.

The FH Range of Universal Oil / Waste Oil Drip Heaters

The Flexiheat “FH” range of waste oil heaters produce clean heat with the use of cheap or even free fuel that simultaneously provides high efficiency. Flexiheat waste oil heaters are durable and reliable products based on testing and feedback from many satisfied customers from the UK and Irish markets. These heaters are equipped with safety devices that prevent overheating and oil spillage of these universal oil heaters.They are are manually fired, and all heater models within this range are equipped with an integral fuel tank which can easily be removed for cleaning purposes.

These warm air waste oil heaters can be the ideal heating solution for the automotive sector such as car garages and workshops, but are also used widely in farm and other industrial heating applications.

Although these heaters are classed as a multi or universal oil heater it is important to know that petro-chemical based oils, solvents, transformer oil, thinners and any oil above grade S.A.E. 90 should not be used in these drip waste oil heaters.

This heating technology can permit the end user to recover the initial investment costs sometimes within one heating season due to the savings made from using our universal oil heater instead of a more expensive fuel oil heater.These heaters are manufactured using the latest technology and have a 12-month warranty on them,which ensures complete customer satisfaction

The high efficiency of the Flexiheat “FH” range of universal oil heaters is achieved by an integral, large heat exchanger, through which all the combustion gases have to pass before entering the flue system. Then depending on the model (as we do one version that is only a radiant heater) a high capacity axial fan draws the air from within the workshop, garage or building over the heat exchanger and combustion chamber and expels this now heated warm air into the area, providing a constant recycling of this warm air.

In order to increase the efficiency of these universal oil heaters, we have designed and manufactured innovative air recuperators, due to this upgrade, the efficiency of our multi oil heaters has improved substantially.

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Download the Flexiheat Brochure for ” FH” Waste Oil Heaters

Firstly we have the 3 smallest units of the range, which are all 20 to 29 kW output models –

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The model “FH105” model comes with no fan and thus is a radiant heat only waste oil heater, the we have the “FH105F” which benefits from a galvanised body, making it a more economical heater and has a warm air blowing fan, which benefits the heaters performance, and will push out 450 metres cubed per hour. Lastly, we have the “FH115” unit, which has a 600 metres cubed per hour fan fitted to the unit.

Then we have the medium heat output range,as shown below –

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The “FH125” and the “FH1250” units have the same heat output of 29 kW to 39 kW, but the “o” model has a galvanised body, making it a more economical heater, for when price is an issue. They both have warm air distribution fans fitted, which are rated at 1,000 metres cubed per hour.

The “FH135” model has a higher heat output of 29 kW to 42 kW, and also has the 1,000 metres cubed per hour warm air fan fitted.

Then we have the largest heat output models of our universal oil heaters –

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Both have the same heating output range of 39 kW to 55 kW, and benefit from a high capacity axial fan providing a heated air flow rate of 2,660 cubic metres per hour.The “FH145C” model differs from the F version in that it has a combustion air inlet of 315mm in diameter, that allows you to duct fresh air into the heater for the combustion process from outside. Thus, ensuring the combustion fan draws in only clean air from the outside the building, and ensures that no dust, vapours or oxygen can be sucked into the heater from the workshop floor.

This range is also available with a small hot water heat changer that can produce hot water for either a central heating system or for domestic hot water demands. The output of this is not large at 6 to 8 kW of output, but nevertheless it can be a great solution for a garage or workshop that has a small office that requires heating via a wet system or requires domestic hot water, via a calorifier or cylinder for washing up or bathing. This version of the heater is designated with the reference “WH” after the figure number.

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A waste oil drip heater that can also produce hot water for a heating system or domestic hot water for bathing from Flexiheat UK

Following is a basic heat loss calculation for our garage / workshop heaters – that you can download and calculate how much heat you require

Heat Loss Calculation for Workshop Heaters – Flexiheat UK

Waste oil heater flue installation

All of the range of the “FH” universal oil heaters have a 150mm (6″) flue pipe connection.All of the heaters are supplied with a draught stabilizer , which is mounted in a tee piece. This draught stabilizer is designed to stabilize and compensate the draught in the flue system.We recommend using a stainless steel flue on our universal oil heaters, aluminium flue is not allowed.If possible, please ensure that the flue system is kept internal to the building, if or when the flue exits the building , then we recommend using a twin wall stainless steel flue system.

If possible , all sections of the flue pipe system should be vertical, in which case the minimum flue height is 5 Metres.The flue should extended at least 0.5 Metres above the ridge to allow the free flow of wind around the the terminal.

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Universal oil heater flue heights

Horizontal flue sections are not permitted,and bends should be avoided if possible.If you have to use bends, then the maximum angle you can use is 45 degrees, and in such cases the minimum flue length then is 7 metres.

Flexiheat Kozy waste oil workshop or garage heaters

The Flexiheat Kozy Warm Air Heater is in reality not only a waste oil heater but a multi fuel heater, as the warm air heater can be fuelled by solid fuel such as wood and coal should this be your preferred or back up fuel in the event of you running out of  waste oil. The Kozy heater range has two models within it , the first is a 20kW Output heater , and this is designated as the Kozy 20  , and the second is the Kozy 30 , which is a 30kW Output model. Both of these heaters require and are powered electrically by a 240 volt , 1 Phase supply.

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The Flexiheat Kozy Waste Oil / Multi Fuel Heater

As you can see from the above picture the Flexiheat Kozy is a warm air heater that benefits from many years of experience of burning waste oil and continuous quality control which has allowed us to produce a solid and durable product whilst maintaining a competitive price.Both models come with a 12 Month warranty and are CE approved.

You will notice that the heaters have two access doors-

The bottom one , is the access door to the burner basin, which is used when burning oils ( Be it waste oil, 35/28 Second Heating Oil/Diesel/Kerosene,vegetable oil,bio diesel etc)  . You remove this burner basin when using solid fuels such as wood, coal , paper etc as these are burnt on a metal hearth, which comes as standard with the heater.This process ensures that it is very quick and easy to change your fuel type.

The top access door gives access to the combustion chamber and flue exit – making cleaning the unit easy. This access door is also used to feed the heater with fuel when using solid fuels.

A high capacity axial fan draws air from the area over the heat exchanger and combustion chamber and expels the warm air into the building, providing a constant supply of warm air.

In times of rising fuel costs, the payback period for a Flexiheat Kozy multi /waste oil heater is very short. Utilising your waste oil, you get an effective warm air heater with no fuel costs, and no fees to pay for the collection and disposal of your waste oil. The Kozy in our opinion is the best small waste oil workshop or garage heater available in the UK and Ireland.

It has been commonly known for years that waste oils, have a calorific value or heating energy, very similar to conventional heating oils. The secret has been to get the oil to burn safely, cleanly, and without any pollution and Flexiheat has been doing this for years with this unit, meaning that you get as much heat as you require, combined with virtually no running costs. These Flexiheat waste oil heaters run cleanly and more importantly efficiently on all engine oils , whether it be hydraulic oil, sump oil, gear oil or transmission fluid. You can literally use it as it comes from your transmission or engine from your machinery or vehicle, without the need for any special filtering.

The Flexiheat “Kozy” range of  waste oil heaters are particularly suitable for heating automotive workshops and garages, warehouses, small greenhouses, etc.They are equipped with a  self contained oil tank of 21 litres ( which is enough fuel for a solid 10 hours of heating ) and are easy to install, being instantly ready for use.

Technical Data for the Kozy Drip Waste Oil Heater

Model  Kozy20Kozy30
Nominal heat outputkW2030
Air deliveryM³/h1,7002,350
Oil consumption * at maximum fireLitres/hr2.0 2.8
Electrical connectionV/A230/1 Phase230/1 Phase
Electrical power consumptionkW0.090.09
Flue pipe connectionØ mm160160
Tank contentlitres2121

Small Waste Oil Heater – Flexiheat Universal or Waste Oil Fired Heaters can be operated on the following fuels –

  • Used Oil , such as engine or gearbox oil (subject to licensing control)
  • 35/28 Second Heating Oil/Diesel/Kerosene
  • Bio Diesel
  • Rapeseed Oil
  • Linseed Oil
  • Certain Vegetable Oils
  • Processed Fuel Oil ( PFO )


  • Wood – for all wood fuels the moisture content can be no more than 20%
  • Waste Wood
  • Logs
  • Coal
  • Paper
  • Cardboard
Waste Oil Heater Maintenance on the Flexiheat Kozy Heater / Waste Oil Garage or Workshop Heater

Well as the saying goes ” you get nothing for nothing in life “. The only thing you will have to give to any small waste oil heater , that is manual ignition , is a bit of your time. Firstly, this waste oil heater is a basic bit of heating equipment and not “high tech” in any form – by this we mean that you don’t have to be a heating engineer to use or maintain the heater.

To start the multi/waste oil heater , you pour a cup of diesel or kerosene into the burner basin, which sits at the bottom of the heater , and then light it with a lit rag or paper, leaving the access door slightly ajar to ensure a supply of combustion air to the heater. After the basin is fully alight , open the fuel supply valve, so that the fuel flowing is literally dripping out, or just slightly above that. Then close the door, and turn on the fan. Waste oil then trickles into the burner basin, where it  vaporizes into a gas and then is burnt very cleanly and efficiently resulting in the heater giving off no fumes or smoke via the flue pipe exhaust system. Any contaminants in your waste oil such as dirt,carbon or detergents are broken down in the 750 °C temperature of the combustion chamber , leaving a crusty dry ash which accumulates in the burner basin , which we recommend cleaning every day . taking about 5 minutes of your time.The amount of ash you will get will depend on the quality and cleanliness of your waste oil , but for example transmission oils leave almost no ash generally, very thick waste engine oil from oil diesel engines leave more ash . Generally , oils from petrol engines , or a combination of waste oils , gives you plenty of heat and very minimal ash.

What a lot of our customers do , is purchase another burner basin off us , so when they start the unit every morning , they use the clean one , then at a time convenient to themselves, they clean “yesterdays burner basin”, making it ready for use in the heater “tomorrow”.But this decision is yours as they say.

I think you agree that these 5 minutes a day , is a small price to pay for the advantage of  warm air heating with free fuel ! 

Installation of the Flexiheat Kozy Waste Oil Workshop Heaters 

The heater must be installed on a completely level, concrete floor.The positioning of the heater in the garage or workshop must be reliant on the following factors –

• A 240 Volt Electricity supply

• The Flue pipe installation

Do not use the Kozy warm air heater in rooms or areas where there are combustible dusts or fumes.These heaters should also have 500mm clearance at the rear of the axial fan, and should also be 500mm off any walls . It is also advisable to have a 2 metre free area around these warm air heaters , ensuring no flammable or temperature sensitive products or items are located withing this area.Please also ensure that you have adequate combustion air / Ventilation as the heater needs this to work.

Warning !! – The Flexiheat Kozy heaters must be operated with their axial fan constantly on during the operation of the heater, and also for 20 to 30 minutes after the fuel being burnt is extinguished otherwise the residual heat can damage the fan.

Never leave the heater unattended

These Waste Oil Workshop Heater can comfortably heat an area of –

Kozy 20 kW = 200 M² ( based on 2.5 Mtrs Height and average insulation values )

Kozy 30 kW =  400 M² ( based on 2.5 Mtrs Height and average insulation values )

But if your in any doubt, please contact us with your buildings volume, and an insulation description and we will do a heat loss calculation for you, to ensure that you get the right kW waste oil space heater for your requirements.

Kroll W401 Heater Information is here and below

Kroll Oil Drip Heaters the W401 Model Features –

  • 35 kW nominal heat input
  • High delta T (80 kelvin)
  • High/ Low manual heat regulation
  • Flame failure safety feature
  • Manual ignition
  • Self-contained oil tank with option for external fuel supply
  • Heavy gauge steel casing with durable powder coated finish
  • Available with or without cross flow fan

Technical Data for the W401 Drip Waste Oil Heater

Model   W401K
Nominal heat inputkW35
Nominal heat outputkW29
Air deliveryM³/h820
Temperature rise (∆T)kW80
Oil consumption *kg/h1.9 – 2.8
Electrical connectionV/A230/0.4
Electrical power consumptionkW0.09
Flue gas pipeØ mm150
Tank contentlitres24

We have just supplied spares to a unit that is 45 years old ! a testament to the quality of this German made unit.

Waste oil heaters for sale

Sometimes these heaters are referred to as waste oil workshop heaters,waste oil drip heaters,drip oil waste heater, small waste oil heater,small waste oil heater for a garage, with thousands sold since its conception , we believe we have the best Waste Oil Heater for sale on the market.Please click here to contact us via email or call us direct on 01202 822221

Download the W401 Kroll Waste Oil Heater Brochure

Download W401 Waste Oil Workshop Heater Manual

Download W401 Spare Parts Document

Download W401 Wiring Diagram