Frequently Asked Questions


What size radiator do I need to heat up my room?

The size will depend on the heat required for the room. This can be established by your plumber/installer.

However, as a guide:
• Calculate the volume of the room by multiplying the height, width and length to get the volume in cubic metres.
• For bedrooms, hallways and kitchens allow 40 Watts per cubic metre, and multiply the total by 40; for bathrooms, living and dining rooms, multiply the total by 50. This will give the output required in watts. Example: A bedroom 3.6m long x 3m wide x 2.4m high has a volume of 25.92cubic metres. Multiply this by 40 to get 1036 Watts.
• If the room has large windows or exposed walls, increase the total by 10%.
• Always choose the next radiator size up if the exact output is not available and allow more length and less height for radiators under a window. Please note that these are only guidelines. There are many other factors which need to be considered like : “tightness” of house (infiltration), walls construction, ceiling and floor construction, heat gain from electric appliances etc. We do not advise an estimated calculation. We recommend to contact our office for assistance.

How do I convert BTU’s into watts?

Divide the BTU’s (British Thermal Units) by 3.414. (for example 5870 BTU’s ÷ 3.414 = 1919 watts). Or to convert watts to BTU’s multiply by 3.414 (for example 1259 watts x 3.414 = 4298 BTU’s).

How can I vent my radiator?

To vent a radiator yourself, some technical skill is required. Either have this done by a technician or get detailed information in advance.

My radiator is making knocking sounds. What does that mean?

One frequent cause of ‘knocking sounds’ at the thermostat valve is interchanging of the flow and return. As a result, the flow in the valve is in the wrong direction. Please contact your technical specialist.

My radiator makes flowing sounds. Why?
There are sounds that could be heard as rushing sounds constantly over an extended period of time. These are generally flowing noises. Generally, these are due to excessively high flow rates (because of excessively high differential pressures) in certain sections of the heat distribution, for example in valves. Flow balancing by a specialist can help.

What does flow balancing mean?
Flow balancing is the limiting of the water volume flows to values that correspond to the heat requirement of the plant. By means of a ‘hydraulic regulation’, which generates the same resistances for all the radiators in a heat distribution network, flow noises, overheated rooms and rooms with a shortfall of heat supply are avoided. In addition, the energy consumption for heat generation and heat distribution are optimized.

My radiator does not reach the required temperature. Why?
There could be several reasons for this: Is the setting of the thermostat sensor correct? Is the radiator correctly deaerated? Is the flow temperature sufficient? Is the circulation pump working correctly? Has the heating plant been flow balanced?

What is the difference between a direct and an indirect system?
A direct system is where the domestic hot water (hot tap water) is connected to a radiator, whereas an indirect system is totally central heating.

What is the hydraulic pressure drop across a radiator?
The pressure drop across a radiator is dependent on the style, size & type of radiator as well as the flow & return temperature. Please contact our office for details.

What is the difference between outputs listed at ΔT60°C and ΔT50°C?
These are a calculation between Flow, Return and Room temperatures. For radiators tested to EN442 a Flow temperature is 75°C, a Return temperature is 65°C and a Room temperature is 20°C. Our outputs are published to ΔT50°C and also at ΔT60°C for those who may have older boilers that may be running at temperatures above 75°C. We can also make calculations for other Flow and Return temperatures if necessary, please contact our office.

What will happen if radiator selections are made from the ΔT50°C tables when the boiler in question has flow and return temperatures of 82°/71°C?
Unless the installer/heating engineer has taken it into consideration when calculating the heat loss requirements of the room, the radiator will be oversized by up to 25%.

The temperature can be moderated by the use of a thermostatic valve, and in the future, when the boiler is replaced with a condensing type the radiators will be of the correct size.

What will happen if radiator selections are made from the ΔT60°C tables when the boiler in question has flow and return temperatures of 75°/65°C?
Unless the installer/heating engineer has taken it into consideration when calculating the heat loss requirements of the room, the radiators will be undersized by approximately 25%, and the room will not be sufficiently heated.

How can one avoid making the wrong selection?
The installer must know the flow and return temperatures of the boiler in question, and select the appropriate ΔT output data for the room.

Are Zehnder radiators suitable for my existing central heating system?

Yes. Our radiators work with all central heating systems. All our connections are BSP and will accept manual or thermostatic valves.

Can I change the radiator(s) in just one room or must I re-do the whole central heating system?
There is no problem with integrating individual radiators into an existing system. When new or additional radiators are being installed, the system should be drained, cleaned and flushed in accordance with BS7593 and a good quality inhibitor, suitable for mixed metal systems, used to protect the system.

I want to change an existing horizontal panel radiator for a tall vertical radiator. Is this OK?
Yes, but if you have a system that has a central heating system expansion tank (usually in the loft), then there should be a 1metre clearance between the top of the radiator and the bottom of the header tank.

Why is it important with some of the models that the flow is in a specific connection position?
Some of the design radiators have baffles inside the water-carrying tubes to divert the water flow around the whole radiator to maximize efficiency.

Can steel and aluminium radiators be put on the same system?
Yes, as long as an inhibitor for mixed metal systems is used. In reality, most systems are mixed metal, as many already have aluminium heat exchangers in the boiler, plus copper pipes and steel radiators.



What is Low-H20?
The first energy efficient radiators available in the UK, Low-H2O stands for low mass and low water content. Low-H2O radiators contain only 10% of the water content and 5% of the thermal mass of a steel panel radiator with equivalent output. With this much lower thermal inert, Jaga Low-H2O radiators can react quicker to external factors allowing you to benefit from free heat sources such as sunshine, cooking, ironing etc. without wasting energy. Low-H2O also stands for low water temperatures: these radiators are actually designed to operate on a supply water temperature starting from 43°C or as low as 35°C for Jaga products featuring DBE technology.

Are all Jaga Low-H2O radiators safe?
Unlike panel radiators, Low-H2O heating is based on convection. This means that the casing doesn’t need to get hot to start emitting heat. Jaga Low-H2O casings are safe to touch at all times, even at high flow temperatures. Within the Jaga LST range, there are even products with soft rounded corners and completely concealed pipe connections – for example the Maxi or Play. That’s why Jaga heating solutions are the first and safest choice for many nurseries, schools, homes for elderly people, health authorities, government departments, leisure centres and public buildings.

How responsive are Jaga Low-H2O heat emitters?
Since they only have to heat up 5% – 10% of the mass of a traditional panel radiator, the reaction time is much faster. The Low-H2O heat exchanger transfers the heat immediately into the room and its low mass means that it stops heating much faster when no longer required. Each second that the radiator is emitting heat after the system is switched off is a waste of energy. A traditional panel radiator or underfloor heating system continues emitting heat for a long time due to its high mass and high water content, whereas Low-H2O responds immediately. An independent test by the BRE (Building Research Establishment, Watford) has confirmed this.

Why is a Low-H2O heat exchanger more efficient with lower water temperatures than any other fin tube element?
Jaga Low-H2O elements are designed to work with low water temperatures. The corrugated fins are developed with a maximum aluminium surface and large contact area with the copper tube. The fin distance is optimised to generate the best airflow through the element when using low water temperatures. The element is based on the principle of a cross flow heat exchanger, whereby the temperature difference between the water and air is always optimal. The short contact distance between the fin and the air reduces the outlet air temperature, this maintains a laminar airflow in the element and means that the warm air does not go immediately to the ceiling but mixes with the ambient room air, just where you want it to become warmer.

Can I use Jaga Low-H2O convectors on a 1-pipe system?
We don’t recommend use on a 1-pipe system as the pressure drop through the radiator is higher than the pressure drop through the pipework, therefore the hot water will take the path of least resistance and bypass the radiator.

My radiator is not hot to touch but the pipes to and from the valve are hot; is this correct?
Yes this is correct. The Jaga design is to have 97% of the output by convection through the top of the radiator which means that the front will only get warm to the touch.

Do I have to use an inhibitor when using Jaga heat exchangers?
No the heat exchanger is made of brass and copper. However you do need to check which inhibitor is needed for the boiler or heat pump and the pipework on the system.

I have a Jaga convector radiator at the moment and would like to change the casing. Is this possible?
If you want to change the casing for a newer or different finish casing of the same size and style then this is not a problem. The casing can easily be changed without draining the heating system.

Are the raw plugs and screws supplied with the radiator?
Fixing packs are supplied with the Low H₂O radiators suitable for use where there is a solid wall construction. However, if the wall construction is not suitable for the fixing supplied, it is the installer’s responsibility to provide the correct fitting.

Your pictures shows the valve on the right hand side. Can I have the valve on the left hand side?
This is possible by turning the Heat Exchanger 180˚. The pipe dimensions are now from the left side of the radiator.

Can I remove and refit my radiators as I am redecorating?
Unlike most traditional radiators, the Jaga casing can be removed without any draining down at all. We recommend the heat exchanger is covered so that paint, plaster etc doesn’t block the fins.

What clearances do I need above and below my Low-H2O radiator to ensure maximum efficiency?
We recommend clearances of 100mm above and below on a radiator with a type 06, 10 &11 heat exchanger, 120mm above & below on a type15 & 16, 150mm above & below on a type 20 & 21, so that the convection is distributed equally.

Low Surface Temperature

When do I need to use a Low Surface Temperature (LST) radiator?
LST radiators are recommended for areas where a person may injure themselves if left in contact with a traditional radiator. Generally we offer LST style radiators for use in hospitals, schools, nurseries and homes for the elderly and other high risk areas where there may be either accidental or prolonged contact with the radiator casing.

Can I have a Jaga LST radiator in a colour other than white?
Jaga LST’s are available in a range of colours, available at a surcharge.

Can I use Jaga Iguana on a 1-pipe system?
We don’t recommend use on a 1-pipe system as the pressure drop through the radiator is higher than the pressure drop through the pipework, therefore the hot water will take the path of least resistance and bypass the radiator.

DBE (Dynamic Boost Effect)

What is DBE?
Our radiators patented Dynamic Boost Effect (DBE) works in harmony with the Low-H2O heat exchanger to deliver maximum output from much smaller radiators even at very low flow temperatures. The microprocessor controlled unit intelligently controls the speed of the incredibly quiet thermal activators to ensure that the correct level of heating is delivered at all times to achieve and maintain a comfortable temperature. DBE equipped radiators warm a room up 9 times faster than a steel panel radiator with a comparable output.

What is the running cost of the DBE fans?
The running cost is extremely low. The Amperage for the different size DBE units are: type 6 is 0.011 amps, type 10 is 0.012 amps & type 15 is 0.009 amps. The power supply draws 0.08 amps from the mains 230V supply.

What is the sound level of the fans?
Calculated Dba running in comfort mode: type 6 & type 15 is 27Dba, type 10 29Dba.

Can the controls be linked together when using multiple radiators?
Yes this is possible. You can run up to six DBA fan units off one power supply.

Can the DBE fans be retrofitted?
Yes, the fans can be fitted at any time. The minimum length of a convector in which a fan can be installed is 600mm.

Can the DBE unit provide cooling?
The standard DBE is not suitable for cooling just heating. We recommend that you also evaluate whether our oXygen ventilation technology might meet your requirements.

What power supply is needed for DBE units?
You will need a standard 3pin 230v-240v plug socket. The power supply (transformer to 12volt) is similar to that of a mobile phone charger in appearance. In most cases the plug socket can be positioned out of sight above the heat exchange within the radiator casing.

Can I use DBE in a bathroom or wet environment?
The 12v DBE is designed so that it can be in a wet area. Please check the regulation for the 240v supply.

The lights keep flashing on my DBE panel control, why is this happening?
Lights flashing indicates that the water temperature in the heat exchanger has not reached the required temperature. If the water temperature is correct and the lights are still flashing, you may need to check that the pipe clips on the printed circuit board are securely fixed to the end curves of the heat exchanger.

Trench Heating

What is the maximum possible length of finned tube in “series” on a Trench heater before expansion joints are required?
We supply heat exchangers up to 4.735 Mtrs long, anything longer than this length, we recommend that you plumb in individually. If you wish to link two shorter lengths together we can offer this as a special. We only advise two heat exchangers to be linked together at any one time.

How is a curved trench made?
The curved Mini Canal trench is manufactured with straight wells & heat exchanges that will be installed underneath the curved grille & frame. The rigid aluminium curved grille & frame are fed through a series of rollers that are set to the correct radius. We cannot offer curved grille in stainless steel however with all other Jaga grilles it is possible to have curved grilles and the minimum radius is 1200mm.

What grilles are available?
We can offer three types of wooden grilles; Oak, Beech & Merbau in natural or varnished. The frame & spacers are dark brown however we can offer natural aluminium frame & spacers which we call the Designo style grille – the slats are closer together. We can also offer rigid aluminium grille in natural, brass, black or dark brown. These grilles can also come as a Designo grille which in this case the slats are closer together. We also offer the Pebbles and Accordion styles which help to make a design statement in any building.

Does the type of grille have an impact on the output?
Yes, the output will be effected by the type of grille you choose. This is due to free airflow through the space between the slats.

Can fan units be incorporated in the trench to gain greater output?
We can offer Mini Dynamic Canal trench heating that has 12volt fans fitted. The minimum trench width for fans to be fitted is 260mm.

Can Trench heaters be mounted in the wall?
This is an option we can offer. Please contact our office for further information.

Can fan assisted Trench heaters be mounted in the ceiling?

I wish to purchase the grille & frame only from your Trench heating product range. Is this possible and what is the depth of the frame?
Yes, you can purchase the grille & frame only. The depth of the frame is 31mm and the minimum width we can offer is 100mm.

Radiant Panels

What heating solutions do you recommend for large spaces?

Radiant ceiling panels provide an optimum energy-saving heating system for large indoor spaces such as gymnasiums, sports halls, warehouses, and production and assembly halls.

This type of space heating solution can reduce energy consumption in large spaces by around 44%. The space heating, ceiling systems are effectively used for warehouse heating or to control the indoor climate in large production halls. Space heating solutions with radiant heating panels can be installed as part of an already existing space heating system or as a complete ceiling heating solution for any large warehouse, production and assembly hall.

How do radiant ceiling panels work?
Radiant ceiling panels work on a fundamental natural principle that is identical to the way in which the sun produces warmth. The heating method is as simple as it is effective: the radiant panels are heated by hot water and give off energy to the room. This energy is converted into heat only when it comes into contact with the human body or other objects.

Can radiant panels be used for cooling as well?
Yes, what is used to heat buildings cheaply and efficiently can also be used to cool them. Cold water flows through the cooling ceiling. Because people and objects in the room have a higher temperature, they radiate their heat to the ceiling. At the same time, the warm air inside the room rises and flows along the ceiling, where it gives off its heat to the cooling ceiling. The cooled air flows back down into the room.

What types of radiant panels do we offer?
Carboline: particularly ideal for hospitals
ZBN: ideal for large spaces such as sports halls
ZIP: ideal for high mounting heights
Alumline: ideal for sound absorption

What is the minimum mass flow rate for ceiling panels?
To maintain the performance given in tables, a turbulent flow must be ensured in the tubes within the panel. This minimum water flow depends on the lowest system temperature. In the case of heating, it corresponds to the return temperature. In case of cooling and combined cooling/heating, it corresponds to the cold water flow temperature. If the minimum water flow per tube is not reached, a reduction in performance of approximately 15% can occur.

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