Underpressure monitor / Chimney 4 Pa

Hey guys,

please don’t slam the blocks so hard around your ears.

The arguments on both sides are correct and each understandable. You are both totally knowledgeable.

However – we live in Germany and have BSFW. With its discretionary power, this discretion has also cost me a whole lot of money, with the heating. My garden partly had to go for it.

A DIBT-certified fireplace (stove) alone is of course really not enough.
If there is a controlled residential ventilation system, it must also have the DIBT certification.
Exhaust hoods and co. come into play. It gets critical at the latest here.

The BSFW can still insist on an underpressure monitor, even if only DIBT-certified things are in the house.
For me, after a *very* detailed demonstration of expertise and checking all documents of the existing technology, he initially waived it. But we monitor it by mutual agreement afterwards.

However, I have taken all precautions to install an UDW. And if the slightest indications should arise, the device will be installed. However, my stove is serviced every year by my chimney builder, seals are regularly replaced, and the chimney is swept 4 times a year. I also do not leave the stove door open.

Anyone building a new house with a fireplace (stove) should definitely install the wiring for an UDW and coordinate with the BSFW. Ultimately it is a question of about roughly 1000 euros.

Now let’s calm the spirits, continue celebrating Easter, and assume that generally an UDW is quite sensible, as well as the fact that BSFW does not generally work strictly according to scientific measures and is allowed to do so.

Best regards
Thorsten

Since I want to install a fireplace and an exhaust hood at my home, I have also dealt with the topic and noticed no arbitrariness. Room-air-independent fireplaces are approved according to DIBT certification (all) up to a negative pressure of 8 Pa. Compliance must be proven to the chimney sweep by calculation or measurement. The latter can be done by himself. For room-air-dependent fireplaces, a negative pressure of <4 Pa must be demonstrated, see the possibilities mentioned above. Alternatively, without proof, a safety device (UDW, window switch) can be installed.

Since the exhaust hood at my place can push out about 750 m³/h, I don't even consider the proof. I will have window contact switches and a temperature sensor installed in the flue pipe. The former costs 100 coins and the latter is worth about 250 € to me for the comfort of not necessarily having to open the window at -10°C.

Good morning everyone,

I have to generally call out Mea Culpa here...

Yes, the assumption is too naive
You have to prove everything to the chimney sweep in black and white; just assuming something doesn't help you.

Indeed, my assumption that a controlled residential ventilation system in 2016 at least met basic safety requirements of the machinery directive was obviously too naive.

Unfortunately, Helios has since confirmed to me that the devices have no internal monitoring or safety functions at all. That means if the supply air fan fails, the device does not shut down (as is actually required by the machinery directive. I fail to understand why these devices are still allowed to be sold) but the exhaust air fan continues to run merrily. Even in the case of frost formation on the heat exchanger, only the supply air is throttled, but not the exhaust air!

In other words, the design concept of the systems obviously was and is not really intended for operation in conjunction with a wood stove (regardless of whether it is room air-dependent or independent)!

Monitoring the motor speeds would cost a few cents to euros. And every car, no matter how cheap, has several differential pressure sensors; this is trivial.

This now means in my understanding:

When installing a chimney stove that is not DIBT-certified, a pressure monitor must be installed anyway, no question.

When installing a DIBT-certified chimney stove, it may work without a pressure monitor. No one can reliably predict this (insofar as the statements of the stove builder and BSFM to me were also not correct). One can only measure in the installed state what happens if the supply air fan fails or something blocks the intake at the highest ventilation level. If I then have less than 8 Pa negative pressure, it is okay. But this will always depend on the tightness of the building and is therefore not universally valid. And the catch: the measurement is strictly only valid for the current weather and especially wind conditions! Whether the chimney draws better or worse with more or less wind, whether any wind vortices from other buildings or trees change the chimney’s draft behavior, no one can tell you.

At that point it becomes a lottery game... the chance of success is low but if it happens, it will be really bad.

For my personal safety requirements, this means:

It is completely irrelevant whether someone would approve it without a pressure monitor. Installing a controlled residential ventilation system together with a wood stove (even a DIBT-certified one) absolutely requires the installation of a pressure monitor. Anything else is playing the lottery with your own life.

Since the DIBT equipment for the stove would also cost me an extra €185, I can actually skip it and install the pressure monitor directly for €380. This limits the additional costs to just under €200.

Best regards,

Andreas

You can also use a controlled residential ventilation system from Zehnder, it has the monitoring. But I found Helios more likeable...

The ones from Vallox also do not turn off

I would like to quickly interject with a possibly "stupid" question. Is a UDW also required for a decentralized "ventilation system"? The supply air in the rooms is provided via Lunos ALD-R 160, so without fans and heat recovery. For exhaust air we have Lunos RA 15-60. It is only a theoretical question. A chimney is present, but a fireplace is still something for the future.