yeah. That’s what I meant with “DIY-Solutions”. Why am I writing this? and why am I so vehemently arguing the point of CERTIFICATION??
So nobody comes to the idea of doing something like this on his/her own. It’s not and I repeat not recommended to do something like this.
The “pulsion” mode (I guess you mean you’re opening a direct air lock from your kitchen to your garage?) is as dangerous in case of emergency as negative pressure. First of all: you don’t know why your house goes into negative pressure: malfunction of the ventilation, some blocked pipes in the ventilation system, whatever. Opening a air lock to the outside (even the idea to open it for a garage with all NOx in that one makes me shiver!) is much more riskier than just shutting the whole thing down. That’s why, there are certified experts looking into life-saving solutions. Not making your own DIY-solution out of thin air. Sorry if I stressed this point and please don’t be offended personally. Unless you’re a certified expert in your field: DON’T RISK YOUR LIFE ON SAVING SOME BUCKS!!
uh. sorry, that even makes it more worse than before. Having an “airtight” house (passive or low energy house) IS THE WHOLE BASIS FOR DRUCKWÄCHTER as the air doesn’t have the possibility to even some under/over pressure through windows or the walls… please @all: ask someone, who knows his stuff, before doing something like this…
Come on… You’re mixing two things up now. You DO KNOW what the problem is when the kitchen hood is ON. It IS the source pressure difference. Seriously… I feel like I’m repeating the same thing. Putting a kitchen hood on IS NOT A MALFUNCTION and should never ever disable my ventilation system. The pulsion vent is also LOCAL which means that it solves the pressure on a room level. The rest of the house remains ventilated (although less efficient).
And the solution for the kitchen hood is not DIY, It can be found built in, in several hoods… So please don’t opinionate the facts.
I guess, we have common ground here:
having negative pressure is bad, if you have an open fire (like we have with our fireplaces). Ok so far?
So, how does negative pressure come into place?
- having (de)central air ventilation, which has a malfunction (my case)
- having a kitchen hood running EVERYTIME it runs (your case)
ad 1)
so, for my malfunctioning air ventilation, the Druckwächter switches the whole thing off => no negative pressure anymore. In parallel the Druckwächter is attached to a alarm signal, which tells me to open all windows possible and leave the house. (if not I’m receiving a warning beforehand from my COx-sensors - I’m not sure, what comes first - and I don’t want to know)
ad 2)
so, now running a kitchen hood without an open (suitable!) window (which one, tells you the expert!) always results in negative pressure - especially if you’re in a airtight house. That’s what you experienced by “causing the kitchen hood not too function properly”. For that one you can either have a Druckwächter (which also shuts down the kitchen hood - and would force you to manually open some window before it allows the hood to turn ON again - or a simple relais, so the hood won’t turn ON, until the window is open. Again: the expert will tell you, which window to use. And that’s why I’m telling you, your DIY solution might have the effect of broadening the consumable air in giving you some air from the garage - at the price of sucking in the air from your garage - not a good idea in my opinion. and depending on the size of the airlock and how “airtight” your garage is - it won’t suffice. But again: I’m not a certified expert either - but I know enough to tell everyone on this forum not to risk their lives doing some stunts to save bucks.
Use Miflora to detect if fire is on, it has temperature and light sensor for 10 eur in a nice package with battery.
Case 1 was never discussed in this thread before so obviously I was giving my input on case 2 as the thread it called “looking for idea’s: fireplace & kitchen hood”.
Case 2 is is essentially the same for the fireplace hence I gave my situation as an example… I can only hope it has given him/her ‘some ideas’ 
And now that we are on the same page…
You don’t need ANY expert to tell you which window to open in case 2. Heck, I will tell you. AS CLOSE AS POSSIBLE TO THE ELEMENT CAUSING THE UNBALANCE WITHOUT ANY OBSTRUCTIONS BETWEEN IT Which is in this case the kitchen hood. In some professional kitchens there is an inlet just below or behind the cooking plate. Which causes the air to rise just above the cooking plate, blowing over the countertop, straight up the hood. Which is a theoretically perfect chimney effect and will catch most of the smell/vapor from your food. Again, this is not DIY, this is available off the shelf.
IMO, this is the same principe they use in closed chimney systems for fireplaces. I’ve only seen those. I can’t comment on any other systems so I’ll refrain from that.
Now, why my garage? Two fold:
- My garage, which is my basement, is naturally ventilated though eight diameter 160 tubes (vertical ends top & bottom) on different sides of the house to use the pressure difference of the wind to it’s maximum. I’m pretty thorough on those things and consulted architect & experienced basement constructors. The only reason I take the air from there instead of outside is that it’s already DRY and slightly WARMER than outside due to the ground buffer effect.
- My garage is aligned just below my kitchen, just it has the perfect position for the chimney effect. I didn’t trust the recirculation technology due to bad past experiences (alhough my hood supports it in case I want to try later on)
PS: my main intent has never been to save bucks, but use the best technique at hand.
you can do what you want with your life. I’ll rest my case here, anybody else can decide what to do with his/her life.
I don’t see how my life is at risk using this technique. At all.
I do think you have made your point repeatedly by now. If you don’t know what you’re doing, don’t potentially endanger yourself and others, and simply don’t mess around with it. But this is very quite trivial on a DIY forum…
Something I don’t understand is how a closed system (original suggestion) does not solve this ?
How can the kitchen hood create unbalance when the fireplace is a closed system connected only to the outside ?
Or is this simply regulation (hence I assumed overregulation), and you need to place the “Druckwächter” & other things anyway?
It would solve this, if its “airtight” (sic!) as a whole, meaning there’s not the smallest inch of openness. Which you only achieve by certified hardware, certified installation and regular Service.
So you need
- the correct chimney construction (in my case I had to tighten it)
- the fireplace which guarantees it’s airtight by certification
- airtight installation using only certified material for the air supply and the gas exhaust to the chimney
- regular service of the system as a whole (changing the seals at the door, the air supply and the chimney connection)
Nevertheless, as my air ventilation detects negative pressure and shuts down itself detecting it - it is not certified. That’s why I had to install the Druckwächter anyways - even though the rest of my whole fireplace was certified and my kitchen hood doesn’t have an external exhaust.
I understand, that this can seem like over-regulation - but it’s not. It truly saves lives. Even the certified fireplace can have a malfunction (be it from too much heat or incorrect handling or whatever).
Ok, got it. Makes sense.
I can only hope that the vendors of closed systems really test and benchmark their products. And not simply think: the customer needs to install a a pressure monitor anyway, so lets take our responsabilities not too seriously. One of the main reasons people take these are safety concerns so it’s kind of important.
In your installation, does the pressure monitor also give you an alert, in what form? sound alert ? is there a risk you might not notice it alltogether?
Can wind conditions affect it negatively? and potentially cause false positives? At what pressure difference (bar/pascal) is it configured?
My installation came from my heating/air ventilation installateur. He used the Leda Controller and as I understood it, that one has some relais, which he used to add a acustic alarm. It’s really loud - but except Tests, I didn’t hear it. I don’t know the settings as this one was done by him and I trust him. Talking about relais - I try to find out in the next service, if I can also attach a simple binary input from the Druckwächter for my KNX-Installation, so I can also handle the alarm in KNX and openHAB.
Wind could affect it, as the whole house could go in negative pressure i was told - as I live in a 1962 built house, renovated 2012 we didn’t go for passive house, but for low energy - so our insulation and window installation isn’t passive house certified. I don’t know the results of the blower door test, but it was quite good for the old house. The field service of Zehnder (my central air ventilation) configured the system and told me, that in certain high winds and storm situations, the house could go in negative pressure, despite the ventilation set to a slight positive pressure. But up until now, even winds in 120km/h didn’t make my Druckwächter go in alarm situation.
Over here in the UK we have rules based on how much heat output of stove (if you have one) you can have before having to install some sort of ventilation near to the fire (under 5KW output requires no extra ventilation). Surely installing some sort of ventilation near the fire would negate the need to only have one or the other on? Another option would be to vent the hood back into the kitchen using a carbon filter or something. Just some suggestions to get around having to build in temperature sensing.
I mesure the exhaust temperature with a PT1000 in the pipe to the chimney with a DS2438 “one wire” client. This is normaly used for batery management, but it is easy to mesure a voltage with this. With a simple voltage divider is this enough for me, because I don’t wont to know the temperature… I only want to know is the fire burning or not. This in combination with an Homematic window contact and a rule works very smart in my installation…