external oil boilers; external oil fired boilers; external oil boiler location; external oil boilers prices;Flexiheat UK

External Oil Boilers – System or Heat Only – 6.1 kW to 40.5 kW Output

external oil boilers; external oil fired boilers; external oil boiler location; external oil boilers prices;

External oil boilers or external oil fired boilers from Flexiheat UK

External oil boilers – Our Evolution range of external oil fired boilers feature some of the highest efficiencies available on the market at present. They are ErP rated “A” oil fired boilers, that comply with all the latest stringent emission regulations as well as the efficiency regulations for oil fired boilers.

These oil fired boilers are a great solution or alternative to an internal boiler, whereby limited space within the property may prevent you using an internal boiler. They also offer some other benefits from being outside the home, such as eliminating the smell of oil that you can get when an oil boiler is located within the home and can be considered safer , as there is no possibility of carbon monoxide poisoning in the event of a flue system failing, that you could get with an internal mounted oil boiler.

All of our external oil boilers are condensing, as they are extremely energy efficient, converting more of the oil burnt into usable heat and ensuring you have the lowest running costs and great value for money. They are located in the ErP “A” segment, which is the very top band of the energy related oil boilers available.

Before we go any further, lets explain the difference between a heat only external oil boiler and an external system oil boiler – we do both here at Flexiheat, so we have both options covered.

Heat only oil boilers

A heat only oil fired boiler, which are also referred to as traditional, regular, conventional or open vent oil boiler, often are found in older homes or properties with an open vented heating system (i.e. an expansion tank located in the roof or loft space). They do the hot water requirements of the property via an indirect hot water cylinder, often located in an airing cupboard.

These boilers are often found in older heating systems, which can easily be converted to what is now termed a sealed heating system or an unvented heating system – which has great benefits.

System oil boilers

A system oil boiler, or a sealed system oil boiler on the other hand has both the pump and the expansion vessel inbuilt to the boiler. This expansion vessel does the job of the header tank /expansion tank or cistern that used to be required in the loft or roof space, and thus eliminates this requirement. The use of a system oil boiler also frees the homeowner from the worry of leaks or frost damage to the header tank, which can not only be a pain but often costly too.

As a system boiler has both the pump and expansion vessel inbuilt to the boiler, they are more compact and space saving, and makes them easier to maintaining and install in the first place.

They still require a domestic hot water cylinder to produce the hot water requirements for the property.

As standard these oil boilers are supplied as a heat only boiler, they are easily converted to a sealed system oil boiler by the optional sealed system kit. This kit basically consists of a high efficency heating pump, heating outlet and return pipes, a check valve, saftey relief valve, filling valve,pressure switch and the expansion vessel sized for the relevant boiler. This kit is fitted within the boiler casing, ensuring a compact and neat installation.

Outside oil boiler;Outdoor oil boiler;System oil boiler external

Hydraulic kit, that is fitted to our outdoor or outside oil boiler, making it a system oil boiler – fits neatly within the boiler casing


If you require a external oil combi boiler, then these are listed on this page here

Adavntages and features of our oil boilers

  • No carbon monoxide poisoning risk – Although, thankfully these days it is not a common occurrence, carbon monoxide leaks are a reality, which can be eliminated by locating the boiler outside.
  • Less noise pollution – When mounted internally boilers, some boilers have a tendency to be noisy, and can become irrorating, with banging, humming or even a vibrating noise – these are eliminated when you locate the boiler externally.The effective acoustic insulation of the body and the boiler housing, as well as the use of an airtight burner, ensures our boilers are one of the quietest on the market.
  • Robust heat exchangers – Our boilers heat exhangers are made of cast iron which is a sturdy and robust material  and it ensures a long service life
  • Easy access for servicing – Being external to the property, this ensures that any heating engineers coming to service or work on your boiler, have easy access, and normally won’t even have to have access to the internals of your property. Thus, servicing for example can be done while you’re not present at home.
  • More internal free space – Not having the boiler in your utility room or kitchen, frees up valuable space within the home. Also, this factor also has another benefit, in that should your internal oil boiler leak, the oil can cause damage and can smell the home out.
  • All of our boilers are supplied with an internal controller and an external temperature sensor as standard, unlike some of our competitors – these are additional extras. This controller and temperature sensor, allows you have a compensated heating system, that adapts to the external weather, and results in lower fuel bills.

Condensing outside oil boilers

Both models in our range of the Evolution outside oil boilers are condensing – as condensing oil boilers provide optimum performance with the lowest running costs and reduced CO2 emissions into the environment, and in majority of cases are required by the building regulations, with regards to oil boiler installations.

Modern condensing oil boilers extract the additional heat from the waste gases (flue gases) by condensing the water vapour produced into liquid water, thus recovering its latent heat. A typical increase of efficiency can be as much as 10-12%.

They are as easy to install as non-condensing oil boilers, but need a connection from the boiler’s condensate outlet to a soak away or drain.

Technical details of the boilers

We do thre models with the evolution range of external oil boilers – The EV20 , EV30 and EV 40 models – below is a quick reference output data chart – thier kW output differs depending on your flow and return temperatures – as you can see.

Outside oil boiler;Outdoor oil boiler;

Quick reference output data for our oil boilers


Here is a full technical chart, with addiontal information

EVOLUTION- External Oil Boilers – ModelsEV 20
EV 30
EV 40
Boiler typeCondensation
Heating only
Rated heat outputPratedkW193040
Useful heat outputP4kW1928.738.7
Useful heat output (30%)P1kW6.18.512.4
Seasonal space heating  energy efficiencyȠS%909192
Useful efficiencyȠ4% (PCI)96.5597.9697.29
% (PCS)91.0492.3891.74
Useful efficiency (30%)Ƞ1% (PCI)103.82103.45104.15
% (PCS)97.997.5598.21
Auxiliary electricity consumption at full loadelmaxkW0.226
Auxiliary electricity consumption at part loadelminkW0.078
Auxiliary electricity consumption in standby modePSBkW0.001
Standby heat lossPstbykW0.1270.1350.17
Emissions of nitrogen oxidesNOxmg/kWh92118119
Heating temperature adjustment rangeºC0 – 85
Maximum safety temperature limit statºC110
Maximum pressure for heating systembar3
Heating expansion vessel capacityLts121414
Heating water volumeLts1419.223.2
Water pressure dropmbar96163272
Fume / Flue gas temperatureºC696783
Volume on fume / Flue sidem30.0940.1140.175
Maximum fume / flue gas flowKg/s0.00850.01320.0186
Fume / Flue gases pressure dropmbar0.20.20.21
Combustion chamber lengthmm220300400
Combustion chamber typeWet, with three flue runs
Burner adjustment typeON/OFF
Electrical supply~220-230 V – 50 Hz – 200 W
Gross weightKg157188217

Brochure and Manual downloads

For full dimensional details and other information, please click on the following to download / open them

Download the External oil boilers- system and heat only brochure from Flexiheat UK

Download Flexiheat Evolution EV ODT External Oil Boiler Manual

External oil boiler location

Our boilers are oil-fired boilers, and the combustion products are therefore removed through an exhaust or flue pipe terminal. The regulations below show the recommend position of the boiler, in relation to the flue exhaust and to various locations.

external oil boilers location; external oil boiler flue regulations; external oil boiler housing;

External oil boilers location and flue regulations – Flexiheat UK


The table above, and the following recommendations must be complied with when installing the boiler:

  • Terminals should be positioned to avoid products of combustion accumulating in stagnant pockets around the building, or entering into the property.
  • If the lowest part of the terminal is less than 2 metres above the ground, balcony, flat roof or other place to which any person has access, the terminal must be protected by a stainless-steel guard.
  • Notwithstanding the dimensions given in the diagram and table, a terminal should not be sited closer than 300 mm to combustible material.
  • Flue gases have a tendency to plume and in certain weather conditions a white plume of condensation will be discharged from the flue outlet which could be regarded as a nuisance, for example, near security lighting.
  • There should be no restriction preventing the clearance of combustion products from the terminal.
  • Where a flue is terminated less than 600 mm away from a projection above it and the projection consists of plastic or has a combustible or painted surface, then a heat shield of at least 750 mm wide should be fitted to protect these surfaces.

Flue Options

Our externally mounted oil boilers are capable of being flued from the rear, left or right hand sides of the appliance as standard.

external oil fired boilers; flue option for external oil boiler; external oil boilers for sale;

External oil fired boilers flueing options from Flexiheat UK

Should the site conditions require it, these oil boilers can be vertically flued with a 100 mm Ø flue system.

external oil boilers prices; external oil boilers for sale;external oil fired boilers

Vertical flue option for these oil fired external boilers

The maximum length of pipe that can be installed is 12 metres (EV 40 ODT) and 15 metres (EV 20/30 ODT). Each elbow of 90°, or two of 45°, reduces the available length by 1 metre, and 1 metre of horizontal pipe represents 2 metres of vertical pipe.

It is recommended that the flue gases outlet pipe be fitted slightly upwardly-inclined 2º to 3º thus preventing water and condensate from being ejected outside.


These oil boilers are designed to burn Kerosene 28 Class C fuel – to British Standard Specification BS 2869 Part 2 Class C2 , European standard BS EN 2869:2010 Class C2, which are also referred to as Heating Oil, 28 Second Burning Oil or Central Heating Fuel. This grade of Kerosene has clean burning characteristics whilst maintain a high heat output and maximum fuel economy.

Installing and maintaining your oil boiler

Your new external oil boiler is a long-term investment into a well built, reliable, high quality product.

Thus, they should be installed by an OFTEC ( Oil Firing Technical Association for the Petroleum Industry) engineer or other suitably qualified person, and the installation should comply with the current Building Regulations and British Standards.

To ensure its maximum product life, it is recommended that servicing and maintenance checks are performed at least once a year, to ensure it continues to operate at peak efficiency and performance, , and therefore, will result in lower running costs and long term reliability

Should you wish to find a local OFTEC qualified installer , please click here

Best External Oil Boilers / Outside Oil Boilers /Outdoor Oil Boilers for sale in the UK & Ireland

Whether you call these oil boilers – external oil boilers, outside oil boilers or even outdoor oil boilers – we have a great quality product,at a great price, being highly efficient and well built, and perfect for your property or home. Should you require anymore assistance or information on our oil boilers for sale in the UK and Ireland, then please don’t hesitate to contact our sales team on 01202 822221 or click here for our email contact form