Cooker Hood Extractor - head scratcher

[R11ysf]

I've had a new kitchen put in and a new telescopic extractor hood fitter. It is direct to pip and extracting to outside.

Now here's the odd bit. I ordered a very powerful one and when turned on it is putting out some serious air from the extraction pipe and is making it to outside the house and I can see the vent flaps moving under the air force. However, even on maximum it barely has the force to hold a piece of kitchen towel against the grease traps so clearly is not pulling the air from underneath - i.e. above the hob.

Any thoughts?

[Sanderling]

The traps do restrict flow a lot. If its sucking up the steam from the hob effectively then maybe you just have too high expectations?

What is the size of the exhaust? To get the most from a powerful extractor you need to use the maximum diameter ducting. Most decent domestic extractors need 150mm ducting for best results. Smooth rigid pipe is best too.

[smokey mow]

You need pressure to hold a paper towel against the grease trap not volume.

Think about blowing up a ballon and a football. Both will hold a similar volume of air but the air in the football will be at a much higher pressure and take a lot more effort to inflate.

[Mark V GTD]

If the hob is installed try it with an open pan of boiling water and see where the steam goes.

[Simpo Two]

Take the grease traps and any filters out - all the crud can blow outside now.

But as said you're comparing apples and oranges; it's designed to remove fumes not paper...

[POIDH]

Are you sure the filters are not still wrapped in plastic ;-)

[Sheepshanks]

R11ysf said:

.... However, even on maximum it barely has the force to hold a piece of kitchen towel against the grease traps...

Funnily enough I tried this the other day on ours, and it was just the same. I checked because it seemed hopeless when doing some steaks - the smoke detector in the kitchen went off and the extractor didn't seem to be doing anything at all, yet outside air was fair blasting out of the vent.

[Bill]

The inlet is much bigger than the outlet so I wouldn't expect anything like as much suck as blow.

Fnar!

[OutInTheShed]

A friend had a 'professionally' installed kitchen, the extractor was put together wrong, sucking from gaps at the top of the housing rather than through the filters.

[Crumpet]

Simpo Two said:

Take the grease traps and any filters out - all the crud can blow outside now.

But as said you're comparing apples and oranges; it's designed to remove fumes not paper...

Given how much muck gets caught in my filters I d say removing them would be a recipe for a very greasy extraction pipe and external vent!

As for the suction, paper sucks flat to the filters on mine - I remember testing it!

[R11ysf]

It is absolutely brand new so zero grease and that was without the grease traps in it. It's pumping out some serious air but definitely not pulling it in from the right place on the bit confused to be honest.

I understand the pressure argument but my old fan which was crap would pull a piece of paper towel up to it and that's was meant to have half the extraction power of this one which is why I won't for such a good model.

[Sanderling]

That doesn't sound right then. I tested mine tonight cooking dinner and it easily holds a sheet of A4 paper on half power.

Can you share the make and model. Was it installed on the same duct work as the original? Any pictures of installation?

Like outintheshed mentioned, I've heard of it where it sucks in through gaps in the sheet metal because they missed something.

Edited by Sanderling on Friday 16th January 20:07

[finlo]

The surface area of the intake is many multiples of the outlet so the velocity at the outlet will be multiples of the inlet.

[motco]

Some extractors are convertible from recirculation via a carbon filter to pass-through to the outside via a duct. It is usually accomplished by moving or rotating a drum or shifting a panel. Check that it's set for the correct mode.

[Sheepshanks]

finlo said:

The surface area of the intake is many multiples of the outlet so the velocity at the outlet will be multiples of the inlet.

The volume of air would be the same though?

Our hob and its extractor are against a wall, with the extractor flush mounted between two wall cupboards - but there's nothing to catch air coming forwards. I find it quite weird that even the steam from a boiling pan seems almost reluctant to go into the extractor and would rather spill forwards into the room. Don't appear to be any air-leaks into the housing, the filters are cleaned in the dishwasher (can see easily through them).

[Rob.]

At risk of turning this into a my-extractor-fan-is-better-than-yours thread, mine can hold a sheet of kitchen towel on the lowest setting...

[Sanderling]

Rob. said:

At risk of turning this into a my-extractor-fan-is-better-than-yours thread, mine can hold a sheet of kitchen towel on the lowest setting...

[Sheepshanks]

Rob. said:

At risk of turning this into a my-extractor-fan-is-better-than-yours thread, mine can hold a sheet of kitchen towel on the lowest setting...

Worst "we use cheap thin kitchen roll" post ever.

[Joe M]

The room can make a difference as well.. If you are in a small enclosed room with the doors shut, the extractor will work better than in a large open plan area.

[motco]

Joe M said:

The room can make a difference as well.. If you are in a small enclosed room with the doors shut, the extractor will work better than in a large open plan area.

As far as airflow is concerned you're better off in a room with a window open as far from the extractor as possible. The outgoing air has to be replaced or you are simply trying to draw a vacuum.