Many homes and buildings suffer from high humidity and the problems it causes; Damp patches, condensation on walls and windows, mould and increased dust mite populations. A good domestic or commercial dehumidifier will reduce the levels of moisture and help to alleviate these problems.

High humidity is a problem that affects many environments. From homes to building sites, wine cellars to swimming pools.

Newer homes are better sealed with double glazing and often have less ventilation; older homes may have solid walls that allow damp to enter into the home. Common causes of excess moisture are drying clothes inside and poor ventilation

A domestic or commercial dehumidifier from Kroll is an ideal solution for so many applications;-

  • Drying out water or flood damaged buildings, eliminating the need to replace and reconstruct
  • Developing stable environments for exposed metal to prevent corrosion
  • Reducing drying times at construction sites for concrete, insulation, and fireproofing
  • Preparing surfaces and vessels for painting and coating applications
  • Blanketing equipment to protect from humid air
  • Maintaining correct ambient conditions for laying of flooring
  • Prevention of mould and fungus growth

Domestic or Commercial Dehumidifier

So, what is Humidity?

 Relative humidity is a measure of how much water is in the air relative to the amount that air could hold if it was saturated. Relative humidity is expressed as a percentage. When relative humidity reaches 100% it is at the “dew point”. In other words the air is “full” of water and that water will start to condense onto any surface. Warm air holds more water than cool air so as air cools relative humidity rises even though the physical quantity remains constant.

For every fall in temperature of 20°F/10°C the capacity of the air to hold water is halved. For example air at 80°F with a relative humidity of 50% will reach the dew point, 100% RH when it has cooled to 60°F.


Performance of dehumidifiers? How are they calculated?

Most dehumidifier manufacturers quote the capacities of their dehumidifiers based on a temperature of 30°C and 100 % relative humidity i.e the temperatures and humidity levels that you would find in Florida, in the summer. The capacity the units will extract is given in litres per 24 hours. If the temperature is lower, as we often find in the UK, then the performance of the unit is lower. Here is an example;-

                                                                                                          Kroll unit                                                       Kroll unit

Temperature & Relative Humidity                        T20D dual voltage  model                       T40D dual voltage model

At 10°C / 60% Relative Humidity                                                       4.2 litres                                                                 8 litres

At 25°C / 60% Relative Humidity                                                       9.5 litres                                                                 20 litres

At 30°C / 60% Relative Humidity                                                       20 litres                                                                  36 litres

As you can see from the above, the colder the temperature, the less water is extracted. At a temperature of 5°C refrigerant dehumidifiers will stop extracting all together


Domestic or Commercial Dehumidifier

What can I do about this, to get my extraction rate up ?

Quite simple, add a heat source to the area to be dried. The best option is an electrical heater or an indirect ( this means the products of combustion do not enter the area being heated ) oil or gas heater. The hotter the area is, the better the extraction rate you will achieve

Airflow is important – You need to ensure that you are using the right size dehumidifier for the area you want to extract the vapour from. The general rule is –

To keep the room dry, multiply the air volume the unit will do by 2

So, for the Kroll T20D it is 160 M³/h thus a room with a volume of 320 M³

To dry a room, multiply the air volume the unit will do by 1

So,  for the Kroll T20D it is 160 M³/h thus a room with a volume of 160 M³

Here’s a quick reference chart for all our models




Room Volume for

Keeping Dry  / m³

Room Volume for Drying  / m³


What can happen if I put 2 smaller dehumidifiers in one room, for example I want to keep dry a 640 M³ building, with two Kroll T20D dehumidifiers?

This isn’t a problem, although you need to evenly place the units within the area, for even extraction to take place. If one side of the room is wetter than the other, expect to see the closest dehumidifier to have extracted more than the other unit.


I’ve just had a phone call from a customer and he says the unit isn’t working, nothing or very little is water is coming out?

We test every domestic or commercial dehumidifier prior to dispatch – the unit is working, if the green light is on – simple as that

It’s probably one of these reasons, why the the performance is poor

  1. Our Domestic or Commercial Dehumidifier units only work down to 30% Relative humidity – the ideal relative humidity is around 50% or less within a living environment –  check what relative humidity you have with a hydrostat. If it’s under 30% the unit won’t work
  2. What’s the temperature within the room? Is there heating within that area? Please bear in mind night time temperatures, where heating systems have be turned off, a room can easily get down to 5°C in the winter – the unit won’t work at 5°C or below , and the performance drops off dramatically with lower temperatures, as stated previously
  3. Do you have windows / doors etc open that is allowing fresh damp air into the area?
  4. Are you using a direct fired oil or gas heater? if so , then this adds water content, that is given off in the combustion process
  5. Is the unit the correct size for the room – please see the above sizing chart
  6. Do you have more than one domestic or commercial d dehumidifier in the room – are they evenly placed? Is one in the in the wetter area?

Domestic or Commercial Dehumidifier


For more information on our domestic and commercial dehumidifier range, please click on our main products page here .  Alternatively, please give us a call on 01202 822222 and our dedicated sales team will be happy to offer advice and assistance or just contact us by mail by clicking here





Waste Oil Boilers

Burning waste oil in order to generate heat is a relatively new way to provide warmth and hot water to households that is becoming increasingly popular among industrial or domestic users. Although, installing a waste oil boiler within one’s home would not be possible, due to its design specifics, it still can be mounted in a garage, shed, workshop or a greenhouse. It is one of the most cost-efficient stand-alone boilers currently available on the market, given that it is using a by-product as a heating source. The price of a waste oil boiler is roughly the same as that of a conventional or gas boiler, but the operational costs are much lower.

A waste oil boiler delivers an efficient way to recycle waste oils as a free fuel source to generate heat and hot water, which can be easily accommodated for a broad range of applications

Waste Oil Boiler

So, what makes a waste oil boiler such a worthwhile investment?

There are a number of advantages to consider

  1. The waste oil boiler can run on any kind of synthetic or mineral oil, being one of the cheapest liquid fuels available on the market at the moment. Listed below are just some of oils you would be able to utilise;-
  • 35 second Heating Oil/Diesel
  • Processed Fuel Oil ( PFO )
  • Rapeseed Oil
  • Linseed Oil
  • Certain Vegetable Oils
  • Used Engine Oil (subject to licensing control)
  • Hydraulic Oil
  • Bio Diesel
  1. A waste oil boiler represents a profitable investment, since all the costs associated with buying and installing the boiler will pay themselves off in a short period, due to considerable savings coming from using the waste oil to run the boiler, which is a very cheap heat source.
  2. An environmentally friendly installation, whereas the boiler does not burn the oil itself but its vapours, which burn without leaving any substantial residual products
  3. A high efficiency rate, which in the case of forced convection can quickly generate a considerable amount of heat that would be enough to warm an area.

Kroll waste oil boilers from Flexiheat UK are your best choice for economical and plentiful hot water and are ideal for so many applications from garages and vehicle workshops to warehouses and distributions centres.

For more information on our waste oil boiler range, please click here  Alternatively, please give us a call on 01202 822222 and our dedicated sales team will be happy to offer advice and assistance or just contact us by mail by clicking here



LTHW Air Unit Heaters

LTHW air unit heaters

Many industrial buildings prefer to run their heating from a piped hot water circuit. Where heat is available in this form then the use of LTHW air unit heaters fed on hot water is invariably the most cost-effective method of space heating a room or building. As with electric fan heaters, there are a variety of types and options available and we aim to make choosing the right model as easy as possible. The following guidance is written around the LTHW unit heaters product range that we call the LH series.



LTHW air unit heaters

Applications for Water LTHW air unit heaters

There is no doubt that if you have a good source of heated water on a piped circuit then these unit heaters are a very cost-effective way to discharge the heat in to the areas in which it is needed. Each model has a large range of heat output depending on the flow temperature, return temperature, ambient air temperature, and water flow rate. This means that with the addition of a recirculation air / fresh air mixer cabinet and suitable controls, these ranges are an ideal compliment to heat sources that are bit less controllable than straight oil gas or electricity fired systems. For biomass boilers, solar fed thermal stores and wind turbine heated thermal stores it is useful to have not only a quick and effective means of dumping excess heat, but also a system that can deliver heat from quite low temperatures and be easy to integrate with a secondary heating system when water temperature is too low.


If you are using water fed LTHW air unit heaters to space heat an area, the implication is that you are using available surplus heat and this will be the principle heating for the area.  As with any heating requirement the initial stage is to identify the size of the heating requirement. Please contact us at Flexiheat UK for advice


It is seldom the case that a required heat output for a system of water fed unit heaters can be met neatly with a single heater. In most cases there are a number of configurations using a number of models from a range to achieve the overall space heating requirement for an application. Sometimes there is a choice between a number of unit heaters of a large size or a greater number of unit heaters at a smaller size.

Generally the smaller number of larger unit heaters will be more cost-effective in terms of unit heaters cost, control costs and installation cost. But the choice of unit heaters should also take into consideration the shape of the room and air throw of heaters, perhaps using larger unit heaters for larger uniform areas, and using smaller unit heaters for smaller dead areas of the main area.

Uses of Fresh Air in Space heating

LTHW air unit heaters

Because the water fed unit heaters usually use a circuit of hot water that is often ‘surplus’ it is quite common that these unit heaters are not merely mounted on wall brackets, in 100% re-circulation mode, but mounted on mixer boxes, which themselves are mounted over a vent in the outside wall, enabling heated air to be a mixture of re-circulated and fresh air.

With the addition of either manual or motorized dampers, the mixer boxes allows the flow to through the unit heater to be set at any level from 100% fresh to 100% re-circulated and anywhere in between.

Mixer boxes are useful because in addition to being able to take air straight from the room through a grill, the grill can be removed leaving an upstand (spigot) for ducting connection, so that the mixing box can be part of a more complex ducted ventilation system.

The key element to connection to a mixing box where outside air is brought in, is that the heater control system incorporates frost protection functionality, to prevent any chance of water freezing in the coils when the heater coils are not being used for general heating.

As well as mixer box options, there are also filter box options allowing a G3 efficiency filter to be fitted. This fitting is essential if the unit heaters are to be used in dusty environments in order that build up of dust on the coils is prevented.


Whilst many will consider conventional boilers to be the heat source of choice for a hot water circuit, they are not necessarily the most flexible source of heat. Water fed unit heaters are not fussy about what heats the water up and will operate perfectly well from a wide range of water feed temperatures. This means that as well as being ideally suited to conventional large boilers, the units can also use relatively low-grade heat produced by chiller/heat pump/ boiler combinations, where the chiller or heat pump preheats water to say 40-50°C  before the boiler adds top temperature to get it to normal heating circuit flow of say 80°C. The benefit of this type of arrangement is that typically the winter heating costs are lower and that in summer the chiller can be used to produce cool water for the heating circuit. Even if you have a heat pump or chiller producing 60°C this is hot enough to be used to feed LTHW air unit heaters, the only difference being that you will get fewer kilowatts out of it than if the flow temperature was higher. The beauty of LTHW air unit heaters is that even for lower temperature flows, they are still a very cost-effective way of discharging heat.

Our LH range of unit heaters from Kroll(A German manufacturer ) offer a wide range sizes and are noted for larger sizes with nominal heat outputs up to 118kw. They are competitively priced and at the bigger end of the range they offer size and output which is beyond the range of most of the other manufactures.

LTHW air unit heaters

The larger Kroll lthw air unit heaters in this range have two fans and at the output at 90/70°C and an ambient air temperature of -15°C the largest LH range heater produces a whopping 203kw. Other useful features in our range are that there are extensive range of options for filter boxes, louvers, and side outlets. There are also options the heaters being supplied with stainless steel casing as an alternative to the standard powder coating. These air unit heaters can also be supplied with explosion proof fan motors, where required.

For more information please visit our  LTHW Unit Heater page , or contact us on 01202 822221  or  visit our website

Automatic Ignition Waste Oil Heater

Automatic Ignition Waste Oil HeaterWaste oil heaters are the best way to get free clean heat! Recycle your waste engine/hydraulic oil with a Kroll SZ Automatic Ignition Waste Oil Heater

Because of the pre heating technology our SZ Automatic Ignition Waste Oil Heater have the ability to burn an extensive range of oils; – waste oil from engines, gearboxes, transmissions, hydraulic systems, or diesel oil. 35 second heating oil/diesel processed fuel oil ( PFO ), Rapeseed Oil,  linseed oil,  certain vegetable oils, used oil (subject to licensing control) and bio diesel

Flexiheat can offer an extensive range of automatic fired units starting at 29kW going up to 187kW. The SZ range are an ideal solution for your heating requirements because of their superior build quality and their capability to burn waste oils thus they not only will give you many years of reliable service but they will reduce your heating costs considerably

KGUB Multi Waste Oil BurnerBelow are just some of the benefits of an automatic fired waste oil heater;-

  • Multi fuel capability
  • Automatic burner with fuel pre-heating
  • High efficiency
  • Fast and simple installation
  • Minimum service and maintenance
  • Clean, soot free combustion


Our range of automatic ignition waste oil heaters are an ideal heating solution for so many applications.   We can even supply  ducted versions , enabling a practical heat transfer from one building to another

At  Flexiheat UK,  waste oil heating  is our speciality. We supply products which are manufactured to very high standards, and which have been designed to withstand the demands of a busy commercial space. Our commitment is to offering high quality heating equipment at highly competitive prices. We understand that budget is an important consideration when you are investing in a new commercial heater, which is why we have worked to develop a product range which offers great value for the money. If you would like to learn more about our commercial heater range or if have a question you think our team can help with, get in touch today and we will be happy to help. Contact  us now to see how we could help to improve and enhance your  premises and most importantly help reduce your heating costs

Manual Ignition Waste Oil Heater

W401K Manual Ignition Waste Oil HeaterFlexiheat UK Ltd is the UK distributor for the Kroll range of heating products. One of the most popular and successful products, which has been manufactured to the same exacting specification for 50 years,  is the W401 manual ignition waste oil heater, capable of burning most oils including waste engine oil, hydraulic oils etc.

Flexiheat can offer two versions of this heater. The W401L, which produces radiant heat only and the W401K, which produces a combination of radiant heat plus hot air from the top mounted  ’thermo’  blower. Both models produce a heat output of 29kW / 99,000 BTU’s

We have supplied many of these units over the years to many different applications. from garage workshops to farm buildings. If you have an abundance of waste oil, then these products are the most economically efficient heating solution

Because of the popularity and overall longevity of these models, component parts have differed little and therefore we carry stock of all common spare parts suited to both older versions and newer versions.

For more information on our manual fired waste oil waste oil heater, please click here  Alternatively, please give us a call on 01202 822222 and our dedicated sales team will be happy to offer advice and assistance or just contact us by mail by clicking here


Industrial & Commercial Electric Fan Heaters

Industrial Commercial Electric Fan HeatersRanging from 3kW single phase to 18kW 3-phase, Flexiheat has a complete range of Electric Fan Heaters to suit both the domestic and industrial environment.

Electric fan heaters are a very good choice for quickly heating small to medium-sized rooms, such as workshops, garages, home offices, and warehouses. They can be used in greenhouses to distribute heat and provide good air movement keeping damp and airborne germs at bay

The Kroll E3 model is 230 volt and with its lightweight design is an ideal solution to heating smaller rooms and offices.

The E8, E12 and E18 models extend to 3 phase and are ideal  for the larger industrial and construction environments such as; warehouse heating, building sites, heat load testing, frost protection, production and manufacturing facilities. The E18SH is a high temperature 18kW unit and is ductable. This unique feature enables the unit to be stationed a considerable distance away from the targeted areas and thus affords the user greater flexibility.   Because of the high temperature feature, the E18SH allows an external room thermostat to be connected thus a more constant temperate can be achieved. This unit is particular suited for the pest control industry.

Find your Electric Fan Heater.

Dual Voltage Dehumidifier for Industrial and Commercial use


Flexiheat UK Ltd is the UK distributor for the Kroll range of Industrial dual voltage dehumidifiers

We have two units within our standard range, these being the Kroll T20D, a 20 litre a day unit, and the Kroll T40D, a 40 litre a day unit.

We have supplied many of these units over the years within the UK market, as we used to supply the Rhino RD4S dehumidifier as well as the Rhino RD2S Dehumidifier, both of which were dual voltage dehumidifiers.



Rhino Dual Voltage Dehumidifier Flexiheat UK

Following the end of the sales agreement with Birchwood products, Flexiheat UK is now selling the replacements for the RD2S and RD4S units direct, please contact Flexiheat on 01202 822221, Email – for current prices, information etc.

We often get asked for rhino RD4S dehumidifier instructions or rhino RD4S dehumidifier instructions as some people refer to, and these are available to download from the Flexiheat UK website – as well as the Rhino RD2S model.

Spares parts are no longer available for the Rhino RD4S or RD2S Dehumidifiers, but please feel free to give us a call and we can quote you for the equivalent models.

You can contact us on 01202 822221 or drop us an email on

Since we stopped manufacturing the Rhino Dehumidifier range for Birchwood, we have moved forward with the design of our dual voltage dehumidifier, and the replacement units are now designated as the T20D, again a 20 litre dual voltage dehumidifier, and the T40D again a 40 litre dual voltage dehumidifier, which have proven to be a big success in the industrial and commercial flood restoration market, as well as the construction industry

Dual Voltage Dehumidifier



On large sites, our large capacity industrial dehumidifiers are perfect for accelerating the drying process of plasterwork and concrete flooring.

The units have changed in appearance, to make them more ergonomically efficient, and easy to transport and lift if required. But the one thing that hasn’t change is the performance and durability of our market leading dehumidifiers, as Kroll being German, don’t ever compromise on quality. That’s why; we believe we have the best dual voltage dehumidifiers on the UK market.

We also do single voltage 240 volt dehumidifiers too, if you don’t require dual voltage. Contact us for details

Kroll UK is now Flexiheat UK – Important News

From the 1st April 2016 Flexiheat UK has become the sole distributor for Kroll Energy GMBH products within the UK and Ireland. Flexiheat UK is a new company that has arisen from the closed Kroll UK Ltd, taking many of the staff from the existing company to the new.

Flexiheat UK’s mission statement is “to provide our customers with quality flexible heating and dehumidification solutions “.

Kroll is one of Europe’s leading manufacturers of Warm Air Heaters and Dehumidifiers

Our Kroll range of both stationary and mobile warm air units, can be fuelled by either heating oil, gas (both natural and LPG) , waste engine oil , or vegetable oil , and throughout its long history, the Kroll name has been synonymous with quality and innovation. Kroll are world renowned for our universal oil burner, which can burn nearly all animal, vegetable and conventional oils (including waste oil).

All of the Kroll products are exceptionally well engineered, energy-saving and meet all technical, economic and ecological requirements