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Components for Flue Gas and Heating Technology

FAQ: The most common questions about our products

On this page you will find the answers to the most frequently asked questions about the products of Kutzner + Weber. Simply click on the desired product group.

Flue Gas Dampers
Secondary-Air Appliances
Chimney Fans


Chimney Fans

What´s the purpose of the Diajekt?

- The Diajekt generates a sufficient draught in the flue gas system. This prevents gasses from streaming back, ensures an efficient combustion and keeps the flue gas system dry.
- If the draught is insufficient or nonexistent, it ensures the required buoyancy.
- In unfavorable conditions (e.g. downdraughts in the mountains), it prevents flue gas from being pressed back down through the chimney into the living space.
- In open fireplaces it prevents soot and flue gasses from escaping into the room.

For which fuels can the Diajekt be used?

- Due to its design and being made entirely of stainless steel (accept the motor), the Diajekt is of a very high quality and suitable for all types of fuels.
- (pressure switch only possible for gas (maybe oil))

Is it possible to use the chimney fan for support during the heat-up phase and operate the fireplace without the chimney fan for the rest of the combustion process?

- Our chimney fans can be used to support the heat-up process without problems. They are not damaged if they are turned off while the fireplace is in use. The maximum outlet temperature of 300°C should not be exceeded.

Are there any circumstances under which the Diajekt must not be installed?

- If there are two or more chimneys in a house, in conjunction with increasingly tight thermal envelopes, the chimney fan may create such a high negative pressure inside the building that the flue gasses of the second chimney are sucked back into the building. In any other case, the Diajekt can be installed on every system. Since the chimney’s cross-section is barely reduced, the fireplaces can still be operated while the Diajekt is switched off. The Diajekt’s zeta coefficient is comparable to that of a rain hood.

Who is authorized to install a Diajekt?

- The installation has to be carried out by a professional in due consideration of the installation instructions of both the Diajekt and the flue gas system. The lightning protection has to follow the corresponding standards, regulations (e.g. VDE regulations) and guidelines.
- As long as specific standards for chimney fans have not been established, please consult your responsible building control to prevent legal issues.

What accessories are needed for the Diajekt?

- For an easier installation of the Diajekt the insertion adapters or square screw plate should be used.
- The Diajekt may also be screwed on directly depending on circumstances.
- In any case we recommend the installation of the vibration damper.

The Diajekt has to be equipped with a maintenance switch in order to disconnect the power e.g. during cleaning.
In order to adjust the Diajekt’s performance to the requirements, the fully automatic control CFC 10, a radio control with timer, a timer with free runtime setting and a speed control for manual, continuous regulation are also available.

How long does the warranty of the Diajekt last?

- Just like all other products of K+W, the Diajekt has a standard warranty period of two years. Its high-quality design ensures that this product will serve you well for a long time beyond that.

Which performance category is the right one for me?
- For individual fireplaces we recommend our models 150S and 250S. These stand out due to a very quiet operation and an adjusted performance. Whether you should choose the 150S or the 250S depends on the diameter of the flue gas system and the required flow rate.
- If there are several fireplaces or a very high draught requirement, we recommend our models RSD 150 to RSD 350.
- When using the S version the RSD pressure switch cannot be used.

What can I do if the Diajekt causes a humming noise in the living area?

- If the flue gas system is very short, and particularly if it is made of stainless steel, an induction noise may be transmitted to the fireplace. Our vibration damper adapter can be installed to absorb this humming. The special design ensures that there is no power loss.

What to keep in mind when using open fireplaces?

 - In general you should be aware that noise may be transmitted into the living space. This is particularly the case with open fireplaces, which is why the Diajekt S version with vibration damper should always be used.

How can the chimney fan be regulated?

- You have four options to choose from for controlling the chimney fan:
o manual speed control
o timer
o radio timer
o fully automatic control CFC 10

Does the chimney fan have to be cleaned?

- The chimney fan should be cleaned regularly by a chimney sweep. This can be done easily and within a few minutes thanks to the quick fasteners. (We know from experience that it is “self-cleaning” when it is operated regularly and with normal fuels (dry wood etc.).)

How does the chimney fan have to be wired?

- Please see the operation instructions.

Under what circumstances is a fully automatic control like the CFC10 necessary?

- If the building contractor demands that the system is monitored, the CFC 10 has to be used. Whenever the operator wants the highest comfort but does not want to switch on the chimney fan manually, the fully automatic control should be used.
- In multi-cascade systems (in connection with the control dampers)

Does the fully automatic control switch off the chimney fan if the draught is sufficient?

- The control continuously measures the negative pressure in the flue gas system and regulates the chimney fan to make sure that this value is maintained. If the natural draught is sufficient or even too strong due to favorable weather conditions, the chimney fan is switched off and if necessary a motor-driven draught regulator is activated.

What is the speed range of the chimney fan that a speed control can regulate?

- The minimum is approx. 700-800 rpm (this is more of a power reduction than a speed reduction)

How long is the silicone tube?

- 2m

Can the silicone tube be extended?

- Yes, but no more than +2m.

How long is the cable of the thermal element?

- 2m

Can the cable of the thermal element be extended?rlängert werden?

- Yes, this has been tested for up to 20m.

What are the resistance values of the chimney fans?

- RSD 150 & 250 = < 1,0 Zeta
- RSD 350  = < 1,5 Zeta
- RS-180 & 225  = 0,0 Zeta

Is a radio control available for the chimney fan so that it isn’t necessary to lay a cable to the fireplace?

- Yes, RS/RSD radio control with signal amplifier (repeater).

What temperatures can the chimney fans withstand?

- 300°C

Can the chimney fan be installed in the connection pipe?

- No.

Does the chimney fan fit on every chimney and what needs to be considered?

- Almost anything can be covered with our adapters.

What is necessary to install the chimney fan on a brick-built chimney?

- The chimney fan can be screwed on directly, but we recommend the use of a square screw plate or an insertion adapter.

When is the insertion adapter absolutely necessary?

- Stainless-steel chimneys.

When is a square plate necessary?

- Preferable for brick-built chimneys.

Why is a maintenance switch necessary?

- A 2-pole maintenance switch is needed to prevent the chimney fan from turning on during maintenance.


Secondary-Air Appliances

Why do I need a secondary-air appliance (draught regulator)?

In order to ensure high-quality combustion and the resulting high efficiency of the fireplace you need consistent operation conditions. The chimney draught is an essential factor for this. This is why all notable manufacturers of fireplaces state in their documentation a so-called “draught requirement” at the fireplace connection and the draught should not fall below or rise above that value. When calculating/planning the flue gas system, this draught requirement is taken into consideration alongside various safety factors and an external temperature of 15° C which is unfavorable for the chimney system (the so-called heating limit temperature).
In practice the safety factors, the use of standard pipe cross-sections and considerably lower external temperatures, particularly in the winter months, generate a much higher chimney draught than calculated. This means, however, that the heating gasses stay in the combustion chamber for a shorter time and this reduces the heat transfer to the surface of the heat exchanger. For the operator of the fireplace this results in higher fuel consumption and increased pollutant emissions.
A high-quality independent secondary-air appliance solves these problems. The flue gas system is provided with “leak air” by opening the control damper precisely and as required, thus limiting the chimney draught and, most importantly, keeping it steady.

What’s the difference between a secondary-air appliance and a draught regulator?

The term “secondary-air appliance” is used in DIN 4795. Colloquially, this is usually referred to as “draught regulator”. It’s one and the same component.

What kind of secondary-air appliance (draught regulator) do I need?

A secondary-air appliance is based on the diameter of the connection pipe. The following three factors are important: effective chimney height, chimney diameter and, to an extent, the output of the fireplace.

What’s the difference between independent, combined and positively controlled secondary-air appliances?

- Independent secondary-air appliance:
An independent secondary-air appliance doesn’t require any additional auxiliary energy. While the fireplace is in use, the control damper is constantly regulating depending on necessity and setting.

- Combined secondary-air appliance (with motor control):
This version is often called motor-driven secondary-air appliance or motor-driven draught regulator. It has the same basic characteristics as the independent secondary-air appliance. In addition, however, the control damper is pushed open with a spring-return drive – only while the fireplace isn’t in use – in order to ventilate the chimney system. During the ordinary operation of the fireplace, the control damper can regulate freely due to the pressure difference between flue gas system and installation room. This model cannot be used with solid fuels.

- Positively controlled secondary-air appliance:
Positively controlled secondary-air appliances are always closed while the fireplace is in use and are only opened when the fireplace is turned off to ventilate the chimney system. This is done via motor control. This version isn’t sensible from a technical standpoint. This is why this type of secondary-air appliances is not part of our product range.


Flue Gas Dampers

I need a flue gas damper (Diermayer damper), which one can I use?

First of all, you need to choose between motor-driven and thermal flue gas dampers. Thermal flue gas dampers must only be used in gas heating appliances of type B11 (atmospheric burner with flow-operated safety device without any kind of fan). For all other types of fireplaces and fuels a motor-driven or manually operated flue gas damper has to be used.

Thermal Flue Gas Dampers
Can I use a thermal damper and if so, which one?

Thermal flue gas dampers must only be installed for atmospheric gas appliances of type B11 (B11 = unit with flow-operated safety device without any kind of fan). In the case of draught burners, solid fuels or liquid fuels you have to use a motor-driven flue gas damper. The DIN 3388 4 contains further information.

GWR ... Thermal flue gas dampers for wall-mounted devices (gas, continuous-flow and circulation heaters, multifunctional devices)

HKS ...   Thermal flue gas dampers for standard devices (gas boilers, storage water heaters, heating elements)

HOS ...   Thermal flue gas dampers for small devices (room heaters, storage water heaters, heating elements)



My heating is too noisy, what can I do?

If there is already a silencer installed in your flue gas system, it probably is an ordinary so-called passive silencer (cylindrical design, porous absorption material like mineral wool or the like). This type of silencer tends to only achieve good silencing values from about 400 Hz upwards; below that they also silence, but considerably less effectively than, for example, at 500 Hz frequency. Depending on the silencer design, the maximum insertion attenuation is approx. 800 – 1000 Hz. This is also what the stated silencing capacity, such as “20 dB”, usually refers to.
Therefore, when a value of, for example, “20dB” is given, this doesn’t automatically mean that a frequency of 20 dB is silenced in the same way as the sum level of about 20 dB. Not only the relatively quiet flow noises can be bothersome, but also the flame noises caused by the combustion itself (explosive volume change). These formation mechanisms create a broad sound spectrum that shows the highest peaks in the low frequency range, approx. 160-250 Hz.

There are four basic solutions available for this problem:

- Passive silencers like AGM... / AVM... / AWM... or AGT...
- Low-frequency passive silencer combination TTSA...
- Sound survey and specific design of a silencer.

If a chimney cover is installed, please note that this may reflect sound waves downwards.

Passive Silencers AGM... / AVM... / AWM... / AGT...

In order to effectively and passively silence heating specific frequencies of 160 – 250 Hz, you need to use sufficiently long silencers (combination of AGM… and AVM…). The elbow silencer AWM… and the muffle silencer AGT… can achieve better, even considerably better, results in comparison to an about equally long straight silencer. This is due to deflections inside the silencer. However, please note that these last two silencer types cause a higher pressure loss.

Low-frequency passive silencer combination “TTSA...”

Another option is the silencer combination “TTSA…” (low-frequency silencer “TTS…” and passive silencer “AVM…”). The combination is designed according to empirical values that we have gathered from several hundred surveys. The main focus of the TTS design was put on the frequency range of 125 to 250 Hz. The insertion attenuation, depending on dimensions, can be found in our price list. 

Sound survey and specific design of the silencer

The optimal solution is to conduct a sound survey of the system while it’s operated on full capacity. Further parameters that should be determined during the survey are the flue gas temperature in the installation room, the flow rate or the available space. Pictures of the installation room are certainly helpful. Of course these can be digital.
The gathered data can then be used to calculate a silencer design that avoids overdesign or underdesign in relation to the individual frequencies as much as possible. This makes it possible to plan a silencer system that is optimized in both cost and performance. On request, we are happy to let you know how to conduct a sound survey or what to measure. However, you are welcome to directly consult one of the sound survey partners of Kutzner + Weber. You can find their contact information on our website at, sorted by postal code. We recommend this for systems where standard products can’t be used, optimal silencing has to be ensured or larger pipe dimensions are present.

Octave and third – what’s the difference?

Three individual frequencies (sounds) are combined in the octave band. This results in a median that can be considerably lower than possible peaks in the third-octave band. The individual third-octave frequencies (sounds) are no longer distinguishable in this median. The big downside is that individual peaks can no longer be recognized as such.