Looking for ideas: Fireplace and kitchen hood

Under certain circumstances it is not allowed to operate an kitchen hood in Germany when the fireplace is burning. A window must then be opened to ensure adequate fresh air supply and the the hood is allowed to operate.

I am now looking for ideas for an automatic system that ensures that the kitchen hood does not start when the fireplace burns.

The main question here is probably fire detection.

Any ideas?

thank you

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What’s about a flame or a temperature sensor or a pressure sensor to detect depression or a airflow-meter?
If you have a damper, you can use the position.

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You have to talk to your “Bezirksschornsteinfeger” (see http://www.schornsteinfeger.de/ if you don’t know) about this issue.
He must accept your kitchen hood in combination with your fireplace and window solution. If you don’t talk to him beforehand, you risk to rebuild the solution from scratch again. He’s responsible for the legal aspects and therefore has the authority to decline your installed solution, if he deems it not suitable for your specific home.

In theory you have two options (AFAIR):

  • install a “Druckwächter” (expensive Version - checking the air for low or negative pressure)
  • install a “Abluftsteuerung” (less expensive Version, checks if window is open - only then the kitchen hood can operate)

but again: talk to your Bezirksschornsteinfeger - and be advised: without a certification no self-constructed solution - especially on some non-certified software on some non-certified hardware (yes, I’m talking openHAB) will suffice! :wink:


Is you kitchen hood smart already, i.e., do you know if it’s on and you can turn it off remotely (through OH or otherwise)?

If so, just create a rule in OH.

    Item Fireplace changed to ON
    sendCommand(kitchenhood, OFF)

Just turn it off when the fireplace is on. By turning it off, I mean disconnect the power source such as through a relay switch. In my local county, it is against code to remotely switch a fireplace, but its perfectly fine to remotely check its state.

I think that’s the most common way to do this.
Some magnetic contact for a window and this enables the functionality.

Maybe one can extend an already accepted solution with some mor openHAB logic afterwards.
But on the first run i would go for a working and accepted solution, even if its not integrated into openHAB then.

Hey Thomas,

thanks for the advice. I am in close contact with my “Bezirksschornsteinfeger” and we are discussing both solution, but i like to have some more ideas. The “Druckwächter” is really expensive and the Windows contact works all the time even if the fireplace is not on.

Thank you for your care.


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This is irrelevant in Germany. The local chimney sweeper has the Overall authority of an open fireplace and all its surroundings (e.g. kitchen hood, heating exhaust (gas, oil, …), air ventilation system, …). Only he decides finally on an accepted solution… and being Germany Germany - you have to have certifications. Without it no “Bezirkschornsteinfeger” won’t accept anything. :wink: In the end, he is responsible for any damage and injuries resulting from bad consulting…


I don’t recall having seen something other than those two… And again: your Bezirkschornsteinfeger must know the solutions… :wink:

:+1: This is the reason I always consult with a licensed technician first before messing with critical stuff

Guys calm down. This is about ideas and not german law. I will never do anything that will harm my family, but it should be allowed to think about things.

The most interesting question is how to detect if the fireplace is on. Ther is no switch, just light some papier and wood with a match

Just measure the temperature near the fireplace. If high enough -> it is ON.

Lots of things you can choose from…

and many more. Hook it up to a $2 ESP01

either measure some output from your fire (heat, exhaust, …) or press a button (dash or some other wireless one?) after igniting the fireplace.

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If that’s the case, just go to the kitchen and turn off the kitchen hood :stuck_out_tongue:


Why don’t use a ‘closed system’ chimney?

IMO your problem is a fireplace design issue. The kitchen hood is actually not even relevant to your problem. Because if you have a closed ventilation system (D - balanced ventilation) you will also have the issue of creating underpressure when your fireplace is burning. Your balanced ventilation system will try to counteract the chimney effect of your frieplace. And sucking the chimney particles back down in your living room.
At the moment you’re focussing on the kitchen hood, but someday it might be another thing that’s causing the unbalance.

So if health and family safety are your main concern, your only real solution is a closed system wheren you take outside air from below the stove, and then use the chimney effect for extraction. And all other suggestions will by default be bad ones :wink:

Two thoughts on that:

  • there are only a handfull of certified closed System (read: expensive!) fireplaces for use in Germany
  • they also do only work 100%, if they are installed by a certified installateur and they have to be checked biannial

and they don’t solve the underlying issue (official accepted overall solution) at all - even for those closed systems my “Bezirkschornsteinfeger” (which is a nice guy, btw!) expected me to have a “Druckwächter” and those certificiations (for my fireplace and my “zentrale Wohnraumlüftung”; my kitchen hood doesn’t have an external exhaust). Yes, it’s Germany and yes, you have to have certifications everywhere. and lastly and importantly (!) the “Bezirkschornsteifeger” is the one responsible for the whole solution.

So, I have installed not only the “Druckwächter” (which shuts down the ventilation in case of low or negative pressure) but also CO and CO2 sensors (certified ones, no DIY) to be on the safe side. The COx sensors were optional.

As Thomas wrote even if it is a closed system …

I’m not aware of German regulation. I live in Belgium, so I’d say we have our fair share of (over-)regulation and can feel your pain. Sometimes there is a big gap between regulation (highly influenced by insurance bureaucrats who only think about their exposure) and actual safety / health. All I want to say is, one might (and will) clash with the other.

I’m only an engineer so I can only focus on the science, and for one I can’t understand how simply shutting off ventilation can ever be a good idea. In case of unbalance (in general) you’re getting air from outside the ventilation system (either in our out from an untrusted source is expected to be bad news) and the solution from the “Druckwächter” is to shut it off and potentially make the problem even worse for the inhabitants ? COx are only ‘some’ of the thousands bad gasses that can build up in your house. Granted, it are the main bad guys, but in modern houses you’re be amazed what else can be found. Also shutting it down might lead to a bacterial-build up which can cause problems later on. So if the shutdown happens regularly, you’re destroying the value of your ventilation system.

So as for the regulation stuff I can’t comment. Talk to the “Bezirkschornsteifeger” as said above. I guess he needs to be willing to ‘warrant’ the system and measures you have in place. Technical and/or procedural.

It’s simple: if you have ventilation, you risk negative pressure. Resulting in sucking gases (and ashes) down the chimney.
That’s why a kitchen hood with an external exhaust has to be prevented from working without opening a suited window. Same goes for ventilation (central or decentral): if for some reason it creates negative pressure same happens. Shutting ventilation down prevents the vacuum. That’s why “Duckwächter” is obligatory in that scenario. I can’t think of a scenario where negative pressure is created in a house without ventilation of any kind.
And I think you don’t understand the underlying physics. Shutdown induced by a “Druckwächter” only happens in emergency! Not even close to regularly! My air ventilation creates a slight positive pressure on purpose; of course this decreases the efficiency of my heating on winter times, but I’ll live with it.

I don’t see overregulation here, as it’s human lives at risk. Otherwise everybody would just install some windy DIY and tell the authorities it worked! That’s why I’m 100% behind those regularities.

My point is that the “Druckwächter” should open an extra pulsion vent instead of just shutting down the ventilation system.
It should solve the problem, and not create an additional one.

Some ventilation systems also have the option to put it into pulsion mode only for a period of time. This could also help you while the kitcken hood is on.

I tried this for my own kitchen hood, but I was losing too much heat during winter as the heat exchanger was totally bypassed. Instead I leave it in balanced mode, but as soon as the kitchen hood goes on, a pulsion event (between garage and kitchen) opens which re-establishes the balance. It closes when the balance has returned. So basically I have built a pressure relieve valve (Druckwächter?).

Edit: I have to add that my house is quite airtight, which was causing the kitchen hood not too function properly due to the unbalance (underpressure) it was causing. So this is similar to your issue. My future gas fireplace won’t have this issue as it will be a closed system.