Length of Kitchen Hood Duct

Georgie Burges

Hi Everyone

I am getting an extension done on my house, and as part of the job, I am moving the kitchen around.

As the house is an end of terrace house, and the cooker will be on an adjoining wall, I won't be able to vent the extractor fan to the outside on the adjoining wall. This means if I want a hood fan that vents, which is my preference as opposed to recirculation, I will have to run a duct approx 5.8 meters long to the opposite wall. There will be one 90 degree elbow where the duct connects with the fan otherwise the 5.8 meter duct is a straight line.

The manufacturer of the hood (Rangemaster) do not recommend anything longer than a 3 meter duct.

Would like some advice if a 5.8 meter duct is advisable or not?

Thanks.

Kevin McCloud

Is there any other wall nearer than the one you have in mind, failing that get a different extractor and up the pipe diameter to compensate for distance.

jack of all

That's a long run of duct to be honest and you run the risk of water (condensate) and grease droplets forming in the duct unless you come up with a better proposal. You should certainly use a smooth wall ducting (110mm or 100mm PVC pipe/ duct) rather than a ribbed flexi, also if you could introduce an in-line fan along the duct length this may help considerably.

gutteruu

Their 3m figure is probably calculated on worst case scenario like a flexi pipe bent a few times. If I were to guess, I'd say you might get away with 1 clear run of PVC as jack of all said (with a good grease filter on hood). If its straight worst case you can get in from outside to clean it. I would have a fall going outside and a trap outside to catch greasy moisture from running down your wall. If all else fails you could get a higher powered extractor and put it outside.

Georgie Burges

Thanks Kevin McCloud - the other options are

1. 3 meter run with an additional 90 degree bend to vent out the extension roof. The problem from what I have read is that the extra 90 degree bend is the equivalent of adding 2 or 3 meters to a straight run anyway. Also I think the that roof vents are ugly as hell (especially on the new zinc roof I am putting on the extension).

2. The only other option would be a straight 3 meter run with no bends, but it would vent across the boundary wall in to my neighbours (beside her back door) so pretty sure she would object to that.

3. Just use the recirculation mode on the fan (there will be plenty of ventilation in the kitchen to get rid of steam).


Thanks Jack of All and gutteruu - was considering using a rectangular duct from a crowd I found online called Luxairhoods, as there will be an RSJ to get past on the straight 5.8m run.

Calahonda52

re 1: could u turn it down through the soffit board, still a bend but at least the gung will fall out:)
what direction are the ceiling rafters in relation to the direction of the duct.

Even if you can move the air quickly enough in the 5.8 run, it will still chill down so could u insulate the duct in the 5.8 run