Cookerhood extraction

[Mikeyo62]

I need to vent to out side, my cooker hood, but the only place available adjacent to the hood is a space next to my Glow worm combi heater. I can not go further away from this point as the floor joists above go the wrong way for an easy run and not too long either. Can anyone advice me on, 'is it safe to have the cookerhood outlet close to the combi outlet, with drawing any unwanted gasses back in, or do new combi's have safer outlets? Regards Mike

 

[Doghouse Riley]

I wouldn't have thought you'd have a problem as both have exhaust vents. The combi does have a pressure sensor safety feature that shuts it down if any exhaust gases get blown back into the flue. But the only ever instance of this of which I'm aware was with a nighbour. Her semi has a drive up the side of her house matched by the semi next door. They have a shared full length car port but with a fence between the two drives.
Early this year, she came over to ask me to have a look at her combi which had stopped working. I found that it had tripped out. I concluded that with the very high winds we had experienced that day, the car port had acted lke a wind tunnel with the wind blowing down between the two houses, enough to put some back pressure on her boiler flue which vents into this area. It hasn't happened since. But that was just air pressure not trapped boiler exhaust gas, That would have just got blown away, not back into the house through a possible adjacent cooker extractor.The feature is in case the flue actually becomes blocked.
If as often the combi is on when the cooker hood isn't, it's unlikely that any gases would enter the kitchen via the cooker hood, as usually houses are warmer than the outside air so there likely will be some air exiting through the cooker hood even when it's off rather than air coming in. Hot air rises, so the low pressure at which the combi vents, the exhaust gases will soon dissipate upwards.

Now that's not an expert opinion, it's just me applying common sense. But someone might tell you different.

We have an extractor fan in the top corner of one of our kitchen windows. This is right next to the flue of our combi. It's been like that for twenty years. I've never given the possibilty of a problem with that situation a single thought.
I'd have no hesitation in doing what you want to do. If you are concerned, buy a CO2 detector patch and stick it on the side of the cooker hood.

 

[Mikeyo62]

I wouldn't have thought you'd have a problem as both have exhaust vents. The combi does have a pressure sensor safety feature that shuts it down if any exhaust gases get blown back into the flue. But the only ever instance of this of which I'm aware was with a nighbour. Her semi has a drive up the side of her house matched by the semi next door. They have a shared full length car port but with a fence between the two drives.
Early this year, she came over to ask me to have a look at her combi which had stopped working. I found that it had tripped out. I concluded that with the very high winds we had experienced that day, the car port had acted lke a wind tunnel with the wind blowing down between the two houses, enough to put some back pressure on her boiler flue which vents into this area. It hasn't happened since. But that was just air pressure not trapped boiler exhaust gas, That would have just got blown away, not back into the house through a possible adjacent cooker extractor.The feature is in case the flue actually becomes blocked.
If as often the combi is on when the cooker hood isn't, it's unlikely that any gases would enter the kitchen via the cooker hood, as usually houses are warmer than the outside air so there likely will be some air exiting through the cooker hood even when it's off rather than air coming in. Hot air rises, so the low pressure at which the combi vents, the exhaust gases will soon dissipate upwards.

Now that's not an expert opinion, it's just me applying common sense. But someone might tell you different.

We have an extractor fan in the top corner of one of our kitchen windows. This is right next to the flue of our combi. It's been like that for twenty years. I've never given the possibilty of a problem with that situation a single thought.
I'd have no hesitation in doing what you want to do. If you are concerned, buy a CO2 detector patch and stick it on the side of the cooker hood.

Thank you for that in-depth explanation. That does make sense to me. It is the only possible route for the extraction pipe to go. Like you say a alarm next to the hood. Cheers.