oil unit heater- oil fired unit heater- oil unit heaters- suspended oil heatersFlexiheat UK

Oil Fired Unit Heaters – Suspended – Warm Air

Oil fired unit heaters – Output range 16 kW to 209 kW warm air heaters

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Suspend Oil Unit Heaters from Flexiheat UK – With Stainless Steel Heat Exchanger & Combustion Chamber

Oil Fired Unit Heaters -The Flexiheat range of oil fired unit heaters are indirect oil fired suspended warm air unit heaters, which have been designed for use in factory or warehouse premises where floor space is at a premium, particularly in areas where supplies of other fuel sources , such as natural gas or LPG gas, may be undependable , uninterruptible or unavailable.

The main advantages of these oil fired unit heaters is the space-saving suspended installation with efficiency, energy saving, comfort and reliability in a compact design that is specially designed for indoor areas that are tight for space. The units suspended from the ceiling – ensuring the entire area under the appliance can be used.

We now have three ranges of oil fired unit heater we can offer, to cover any of your oil warm air heating requirements

The first range is our “FHOUH” range of  oil fired unit heaters, which can be room sealed, taking the combustion air from outside to the building, and expelling the exhaust gases ,(or often referred to as the products of combustion) externally.

The following oil fired unit heaters are fully compliant with the Eco-design Directive (2009/125/EC) ErP Lot21 – 2021

The Flexiheat “OUH” oil fired unit heater range can be supplied in axial fan free blowing configuration, which are normally installed directly into the space being heated, or a centrifugal fan option for ducted applications. The range of oil-fired unit heaters is comprised of 3 models with outputs ranging from 30kW to 70kW of output power.

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These suspended oil fired unit heaters are to provide comfort for the occupants of a heated space – and emit NOx levels less than 100 mg/kWh.

The flue gas exhaust exit is on the side of the heater, and at the rear is a connection that allows you to bring the combustion air into the unit heater, if so required. When this is done, the units can be deemed a room sealed oil heater. Or you can use the combustion air from within the building – it’s your choice, to suit your site requirements.

This oil fired unit heater range can be flued horizontally, we recommend a maximum length of 5 meters (the use of bends reduces this length)

The following oil heaters can be used with Gas Oil Only, also popularly known as red diesel or Class D, 35 second burning oil, Marked EN590

Oil heater     Oil heater – Free Blowing Heaters with Axial FanOil heater – Centrifugal Fan Heaters – for Ducting
Heat output (kW)32.353.77632.353.776
Useful Power (kW)305070305070
Efficiency (%)939392939392
Oil flow rate (kg / h)
Rotation speed (rpm)1,0001,0001,0001,0001,0001,000
Air flow (m3 / h)4,6004,6009,2003,5005,00010,000
Temperature rise – Δ T (° C)193222252921
Motor Power (W)3703702 x 3707367362 x 736
Available Pressure (Pascal)160160170
Diam. Flue outlet (mm)125153153125153153
Sound level (db)545868

Please note that the two following ranges of suspended oil heaters can only be used for non-comfort heating i.e. – not heating people, as they are not ErP compliant and can only be used in applications such as – horticultural heating – e.g., glasshouses, frost protection of perishable products, agricultural heating – e.g., poultry houses or process heaters/dryers.


The GE models are units having axial fans – free blowing warm air oil heaters
The GC models are units having centrifugal fans – for the heating of environments with ductwork

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Horizontal Oil Fired Unit Heater from Flexiheat UK

  • 10 YEARS GUARANTEE on the heat exchanger and the combustion chamber ** , as they are both made of stainless steel
  • AUTONOMOUS in its operation
  • EASY & Flexible installation for any commercial or industrial oil warm air heating applications
  • SUITABLE for various applications
  • EXTREMELY QUITE during its operation from 51 -61 dBA dependent on the model
  • FUEL TYPE: Oil – Gas Oil Only, also popularly known as red diesel or Class D, 35 second burning oil, Marked EN590
  • TWO-STAGE VERSION- With Hi / Low Oil Burners available on the 85 and 100 oil heaters
  • CENTRIFUGAL FAN –  with up-rated air pressures , for warm air ducting applications  -the version “GC”  donates Centrifugal models
  • Outputs ranging from 16kw to 92.9 kW

* The guarantee depends on regular maintenance
** ON/OFF operation for all the diesel oil model, also if combined with INET control panel

Oil Unit Heater Technical Table

Oil fired unit heater / Suspended oil heaters : Technical features

  • High efficiency operation > 91% with light diesel oils
  • The new stainless steel combustion chamber is able to guarantee high efficiency and reduced load losses.
  • The dimensions of the heater have been reduced and it doesn’t require a lot of space. Thanks to its new design it is suitable for all the kinds of heating applications.
  • These air heaters are CE certificated for type C Flue installations (external air intake and fume exhaust with airtight connections). See below –flue systems for oil unit heaters; horizontal oil-fired unit heater; Suspended oil heaters; oil fired unit heaters;
  • The oil burner is positioned in a separated housing or compartment, easy to be inspected, airtight, with IP45 electrical protection

Oil Fired Unit Heater Installation

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Oil fired unit heater – Horizontal flue kit – on the left is the combustion air inlet pipe (made from galvanised steel) and on the right is the combustion gases or flue gases terminal (which is made from stainless steel) this way of flueing the suspended oil heater allows you to have a room sealed heater.

Because this oil fired unit heater range can have the flue pipes or chimney exiting the building horizontally , this make them very easy to install , as well as cheaper , as no cranes , lift etc are required to install the flue pipe , especially when the units are installed at low level / ground level – not to mention the health and safety requirements at working at heights are eliminated – So no more of this – and the expense and health and safety associated with it.

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Oil Fired Unit Heaters – Supply Pipe Distances –

We use the Riello oil burners on this range of unit heaters which are high quality and a well-known brand, and we often get asked how far the pumps on the oil burners will lift the oil and how far horizontally in metres the pipework can be , so below is a chart , show the head either positive or negative in relation to the burner level – which cannot be more than 4 metres for either configuration , and how far horizontally the oil pump will work .

Please note that the measurement of the ” Head ” of the burner must be taken form the lowest point in the oil tank (less 100mm or 10cm’s as recommended, as you don’t want the oil tank suction pipe in this lower level, due to the risk of contaminants such as debris and water in the oil, which would settle here. The Type “A” is referred to as a “twin pipe oil system ” which has a feed and return pipe, and the Type “B” is referred to as a “single pipe oil system ” which just has the feed pipe to the oil burner.

In a nutshell, if you use a twin pipe oil system, you can longer distance than a single pipe system, and for either system if you use a larger diameter bore on your pipework, again you can go a further distance to your oil tank


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As usual we always recommend that our oil fired unit heaters are installed by a competent installer, preferably an OFTEC approved one

Download the Oil Fired Unit Heaters Brochure – FHOUH Range

Download Oil Fired Unit Heater Manual

Oil Unit Heaters – From 52kW to 208kW – Our Agri-P Range

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Suspended Oil Heaters from Flexiheat UK

These warm air heaters can be used in either a free blowing or flexible ducting air distribution, working with a light oil burner. The stainless steel combustion chamber and heat exchanger are constructed in stainless steel AISI 430, either with high performance axial or centrifugal fans, electronic control and safety system. These oil unit heaters are robustly constructed ,manufactured by galvanized pre-coated steel panels fitted with radiant sheet insulation.

Please note that this range of suspended oil heaters can only be used for non-comfort heating i.e. – not heating people, as they are not ErP compliant and can only be used in applications like this –

• Horticultural heating – i.e. glasshouses
• Frost protection of perishable products
• Agricultural heating – i.e. poultry houses
• Process heaters/dryers

Which are exempt from the ErP warm air heating regulations and standards.

The range of  5 models have been designed for : warehouse heating, greenhouses heating, factory heating ,workshop heating or basically any where you would like to use oil as your heating fuel, and keep the heater off the floor . A huge range of accessories is available for heater range. Another great benefit of this heater range , is that they can be flued horizontal , for a maximum of 3 metres , which often saves in the time and hassle factor , as opposed to flueing these oil fired unit heaters vertically through a roof.

The Flexiheat oil unit heaters can be supplied in axial fan free blowing format, to be installed directly into the space to be heated, or with centrifugal fan for ducted applications. Heaters are generally arranged for on/off operation.

Oil fired unit heaters / Horizontal oil-fired unit heater – Key Features
  • Indirect Oil fired
  • Compact oil unit heater
  • 35 sec or 28 sec oil
  • Stainless Steel combustion chamber and heat exchanger
  • All units are high efficiency
  • Axial or centrifugal fans option
  • Choice of outputs: 52.2kW, 74kW, 100.8 kW,152.3kW and 208.8kW
  • The 52.2kw ,74kw and 100.8 kW models are 240Volt / 1 phase powered, with the 152.3kW and 208.8kW being a 3 phase /400Volt heater

The special stainless steel heat exchanger: The heart of the machine

Oil Unit Heater Heat Exchanger

With our patented highest efficiency heat exchanger, with air flow completely in counter current to the exhaust flow, made exclusively in 18% chromium stainless steel, which guarantees total protection against corrosion, both from humidity and combustion by-products.

The heat exchanger is made up of:

– Combustion chamber, cylindrical flame inversion model, perfectly cooled at every point, with outlet to oil-fired burner and visual control of flame

– Exchange elements, inclined upwards, with flat tubular section exhaust flues and with swirl impressions for maximum thermal efficiency.

– Exhaust manifold with wide inspection door for easy cleaning of the exchanger and chimney inlet.

These oil unit heaters are available with various different option, below in the left hand picture you can see the horizontal unit , fitted with a two way air plenum with clear warm air distribution duct attached, and in the right hand picture , you can see the vertical oil unit heater option, again fitted with a clear warm air duct, these heaters a very popular choice for industrial and commercial greenhouse heating applications

oil unit heaters - greenhouse heaters

Oil Unit Heaters – Fitted with clear warm air ducts ,a perfect solution for greenhouse heating

This Unit Heater Range is certified in accordance with :

Gas Directive 90/396/CEE

Low Tension Directive 72/23/CEE

Machine Directive 89/392/CEE

Electromagnetic Compatibility Directive 89/336/CEE

Free blowing models are fitted with axial fan sets and discharge warmed air directly into the heated space via adjustable louvered horizontal grilles. Centrifugal fan models are fitted with a centrifugal fan close-coupled directly to the heater casing. The burner , along with the fan and high limit stat, are externally mounted, giving good and easy access to them when servicing the unit. The stainless steel combustion chamber and heat exchanger , which are guaranteed for 10 years gives you a reliable and long life suspended oil heater.

The range has been designed for use in factory or warehouse premises where oil fired heating is a requirement and floor space is at a premium.

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Oil Fired Unit Heater – Suspended from chains

Oil Fired Unit Heaters for Sale UK and Ireland

Should you require anymore assistance or information on our oil fired unit heaters / Suspended oil heaters / Oil unit heaters ,please don’t hesitate to contact our sales team on 01202 822221 or click here for our email contact form, please note we can also supply these heaters with either natural gas or a propane gas burner if so required.