Hello,

My hob has a cooker hood above it but it has been installed in
re-circulation mode. If I change the carbon filter it might absorb
smells but it will not do anything about steam, so I would like to
convert it to extract outside. That would be straightforward: the hood
is about 6.5' or 2m ish from the wall. I could run ducting along the
top of the cupboard units.

What ducting is best: circular or rectangular? I know the oblong one
can be hidden behind a pelmet but I'm happy to have unsightly circular
if that is better - does one shape offer less resistance to the air?

The thing that may be a problem is that the wall is only 2' wide. Then
there is a french door in the wall and I'm not sure whether there is a
lintel above it.

I'm just wondering whether I can cut a 6" hole in the wall for the
extractor fan if the wall is only 2' wide; that's a quarter of the
width of the wall, which sounds a lot.

OTOH I live in a semi, so although I only have 2' on my side, there is
another 2' on my neighbours side which mirrors mine.

What do you all think?

Thanks.

On 30/06/2019 09:04, Stephen wrote:
Hello,

My hob has a cooker hood above it but it has been installed in
re-circulation mode. If I change the carbon filter it might absorb
smells but it will not do anything about steam, so I would like to
convert it to extract outside. That would be straightforward: the hood
is about 6.5' or 2m ish from the wall. I could run ducting along the
top of the cupboard units.

What ducting is best: circular or rectangular? I know the oblong one
can be hidden behind a pelmet but I'm happy to have unsightly circular
if that is better - does one shape offer less resistance to the air?

The thing that may be a problem is that the wall is only 2' wide. Then
there is a french door in the wall and I'm not sure whether there is a
lintel above it.

I'm just wondering whether I can cut a 6" hole in the wall for the
extractor fan if the wall is only 2' wide; that's a quarter of the
width of the wall, which sounds a lot.

OTOH I live in a semi, so although I only have 2' on my side, there is
another 2' on my neighbours side which mirrors mine.

What do you all think?

Thanks.

Modern house presumably? Cavity wall with insulation?

*Probably* not a lintel at the place you would want to make the hole,
which is presumably at the junction of the party wall and one side of
your 2 foot wall.

Not sure what if any implications there are for putting vent close to
your neighbour.

With a 2 metre straight run I would not worry about pressure drop in
rectangular duct.

Can't see a 6 inch hole having structural implications, especially as it
is probably nearer 4 inches.

On 30/06/2019 09:04, Stephen wrote:
Hello,

My hob has a cooker hood above it but it has been installed in
re-circulation mode. If I change the carbon filter it might absorb
smells but it will not do anything about steam, so I would like to
convert it to extract outside. That would be straightforward: the hood
is about 6.5' or 2m ish from the wall. I could run ducting along the
top of the cupboard units.

What ducting is best: circular or rectangular? I know the oblong one
can be hidden behind a pelmet but I'm happy to have unsightly circular
if that is better - does one shape offer less resistance to the air?

The thing that may be a problem is that the wall is only 2' wide. Then
there is a french door in the wall and I'm not sure whether there is a
lintel above it.

I'm just wondering whether I can cut a 6" hole in the wall for the
extractor fan if the wall is only 2' wide; that's a quarter of the
width of the wall, which sounds a lot.

OTOH I live in a semi, so although I only have 2' on my side, there is
another 2' on my neighbours side which mirrors mine.

What do you all think?


If using rectangular ducting then you would be better off with a brick
grille.



--
Adam

On 30/06/2019 09:04, Stephen wrote:
Hello,

My hob has a cooker hood above it but it has been installed in
re-circulation mode. If I change the carbon filter it might absorb
smells but it will not do anything about steam, so I would like to
convert it to extract outside. That would be straightforward: the hood
is about 6.5' or 2m ish from the wall. I could run ducting along the
top of the cupboard units.

What ducting is best: circular or rectangular? I know the oblong one
can be hidden behind a pelmet but I'm happy to have unsightly circular
if that is better - does one shape offer less resistance to the air?

The thing that may be a problem is that the wall is only 2' wide. Then
there is a french door in the wall and I'm not sure whether there is a
lintel above it.

I'm just wondering whether I can cut a 6" hole in the wall for the
extractor fan if the wall is only 2' wide; that's a quarter of the
width of the wall, which sounds a lot.

OTOH I live in a semi, so although I only have 2' on my side, there is
another 2' on my neighbours side which mirrors mine.

What do you all think?

Another option that I have used before is to install the ducting between
the joists esp with the chimney hoods.


--
Adam

On 30/06/19 09:18, newshound wrote:
On 30/06/2019 09:04, Stephen wrote:
Hello,

My hob has a cooker hood above it but it has been installed in
re-circulation mode. If I change the carbon filter it might absorb
smells but it will not do anything about steam, so I would like to
convert it to extract outside. That would be straightforward: the hood
is about 6.5' or 2m ish from the wall. I could run ducting along the
top of the cupboard units.

What ducting is best: circular or rectangular? I know the oblong one
can be hidden behind a pelmet but I'm happy to have unsightly circular
if that is better - does one shape offer less resistance to the air?

The thing that may be a problem is that the wall is only 2' wide. Then
there is a french door in the wall and I'm not sure whether there is a
lintel above it.

I'm just wondering whether I can cut a 6" hole in the wall for the
extractor fan if the wall is only 2' wide; that's a quarter of the
width of the wall, which sounds a lot.

OTOH I live in a semi, so although I only have 2' on my side, there is
another 2' on my neighbours side which mirrors mine.

What do you all think?

Thanks.

Modern house presumably? Cavity wall with insulation?

The OP needs to watch out if the cavity wall insulation is old
polystyrene beads which no longer stick to each other. When the hole
saw is removed the stuff will just pour out (especially if it's a
standard two-storey house and the hole is at the top of the ground
floor). I would advise him to have a vacuum cleaner ready and to shove
the ducting in a soon as possible after the hole saw is pulled out.

--

Jeff

Stephen formulated on Sunday :
Hello,

My hob has a cooker hood above it but it has been installed in
re-circulation mode. If I change the carbon filter it might absorb
smells but it will not do anything about steam, so I would like to
convert it to extract outside. That would be straightforward: the hood
is about 6.5' or 2m ish from the wall. I could run ducting along the
top of the cupboard units.

Check which way the joists in the floor/ ceiling above run, you might
be able to fit a suitable duct between joists. That is how I did my hob
extract. Rigid plastic pipe up from hob into ceiling, then duct between
joists, terminating in a gravity closing terminal on the outside wall.

On Sunday, 30 June 2019 09:41:32 UTC+1, Jeff Layman wrote:
On 30/06/19 09:18, newshound wrote:
On 30/06/2019 09:04, Stephen wrote:
Hello,

My hob has a cooker hood above it but it has been installed in
re-circulation mode. If I change the carbon filter it might absorb
smells but it will not do anything about steam, so I would like to
convert it to extract outside. That would be straightforward: the hood
is about 6.5' or 2m ish from the wall. I could run ducting along the
top of the cupboard units.

What ducting is best: circular or rectangular? I know the oblong one
can be hidden behind a pelmet but I'm happy to have unsightly circular
if that is better - does one shape offer less resistance to the air?

the big difference is between smooth walled & corrugated flexible, The latter is bad news for airflow, especially with axial fans which only deliver low pressure.

The thing that may be a problem is that the wall is only 2' wide. Then
there is a french door in the wall and I'm not sure whether there is a
lintel above it.

I'm just wondering whether I can cut a 6" hole in the wall for the
extractor fan if the wall is only 2' wide; that's a quarter of the
width of the wall, which sounds a lot.

OTOH I live in a semi, so although I only have 2' on my side, there is
another 2' on my neighbours side which mirrors mine.

What do you all think?

Thanks.

6" in 4' should not be a problem

Modern house presumably? Cavity wall with insulation?

The OP needs to watch out if the cavity wall insulation is old
polystyrene beads which no longer stick to each other. When the hole
saw is removed the stuff will just pour out (especially if it's a
standard two-storey house and the hole is at the top of the ground
floor). I would advise him to have a vacuum cleaner ready and to shove
the ducting in a soon as possible after the hole saw is pulled out.

Drill an 8mm test hole. You can block that trivially easily if it rains beads.


NT

On Sunday, June 30, 2019 at 11:01:37 AM UTC+1, wrote:
On Sunday, 30 June 2019 09:41:32 UTC+1, Jeff Layman wrote:
On 30/06/19 09:18, newshound wrote:
On 30/06/2019 09:04, Stephen wrote:
Hello,

My hob has a cooker hood above it but it has been installed in
re-circulation mode. If I change the carbon filter it might absorb
smells but it will not do anything about steam, so I would like to
convert it to extract outside. That would be straightforward: the hood
is about 6.5' or 2m ish from the wall. I could run ducting along the
top of the cupboard units.

What ducting is best: circular or rectangular? I know the oblong one
can be hidden behind a pelmet but I'm happy to have unsightly circular
if that is better - does one shape offer less resistance to the air?

the big difference is between smooth walled & corrugated flexible, The latter is bad news for airflow, especially with axial fans which only deliver low pressure.

The thing that may be a problem is that the wall is only 2' wide. Then
there is a french door in the wall and I'm not sure whether there is a
lintel above it.

I'm just wondering whether I can cut a 6" hole in the wall for the
extractor fan if the wall is only 2' wide; that's a quarter of the
width of the wall, which sounds a lot.

OTOH I live in a semi, so although I only have 2' on my side, there is
another 2' on my neighbours side which mirrors mine.

What do you all think?

Thanks.

6" in 4' should not be a problem

Modern house presumably? Cavity wall with insulation?

The OP needs to watch out if the cavity wall insulation is old
polystyrene beads which no longer stick to each other. When the hole
saw is removed the stuff will just pour out (especially if it's a
standard two-storey house and the hole is at the top of the ground
floor). I would advise him to have a vacuum cleaner ready and to shove
the ducting in a soon as possible after the hole saw is pulled out.

Drill an 8mm test hole. You can block that trivially easily if it rains beads.


NT

Yes. Flexible hose kills the efficiensy of the air flow handling . Also get the largest size recommended by the extractor manufacturer. SWMBO got a Miele fan and it could cope with 6" pipe. I used smooth wall plastic pipe. It works perfectly. Even frying fish laves no residual odours in the kiytchen and no steam at all

On 30/06/2019 09:04, Stephen wrote:
Hello,

My hob has a cooker hood above it but it has been installed in
re-circulation mode. If I change the carbon filter it might absorb
smells but it will not do anything about steam, so I would like to
convert it to extract outside. That would be straightforward: the hood
is about 6.5' or 2m ish from the wall. I could run ducting along the
top of the cupboard units.

What ducting is best: circular or rectangular? I know the oblong one
can be hidden behind a pelmet but I'm happy to have unsightly circular
if that is better - does one shape offer less resistance to the air?

The thing that may be a problem is that the wall is only 2' wide. Then
there is a french door in the wall and I'm not sure whether there is a
lintel above it.

I'm just wondering whether I can cut a 6" hole in the wall for the
extractor fan if the wall is only 2' wide; that's a quarter of the
width of the wall, which sounds a lot.

OTOH I live in a semi, so although I only have 2' on my side, there is
another 2' on my neighbours side which mirrors mine.


Are you able to download installation instructions for the hood?

I was able to buy a part that connects the round pipe inside the hood to
a square pipe that runs along the top of my cupboards. The square pipe
was a standard part which terminates in a brick coloured plastic vent
in my outside wall.


--
Michael Chare

On 01/07/2019 17:27, Michael Chare wrote:
On 30/06/2019 09:04, Stephen wrote:
Hello,

My hob has a cooker hood above it but it has been installed in
re-circulation mode. If I change the carbon filter it might absorb
smells but it will not do anything about steam, so I would like to
convert it to extract outside. That would be straightforward: the hood
is about 6.5' or 2m ish from the wall. I could run ducting along the
top of the cupboard units.

What ducting is best: circular or rectangular? I know the oblong one
can be hidden behind a pelmet but I'm happy to have unsightly circular
if that is better - does one shape offer less resistance to the air?

The thing that may be a problem is that the wall is only 2' wide. Then
there is a french door in the wall and I'm not sure whether there is a
lintel above it.

I'm just wondering whether I can cut a 6" hole in the wall for the
extractor fan if the wall is only 2' wide; that's a quarter of the
width of the wall, which sounds a lot.

OTOH I live in a semi, so although I only have 2' on my side, there is
another 2' on my neighbours side which mirrors mine.


Are you able to download installation instructions for the hood?

I was able to buy a part that connects the round pipe inside the hood to
a square pipe that runs along the top of my cupboards. The square pipe
was a standard part which terminates in a brick coloured plastic vent
in my outside wall.


IIRC Wickes has various "standard" adaptors, like a round to rectangular
elbow, that may well fit generic hoods. You might have to apply a few
turns of duct or PVC tape to make them a push fit instead of a loose one.

On Sun, 30 Jun 2019 09:18:49 +0100, newshound
wrote:

Modern house presumably? Cavity wall with insulation?

1930s. Cavity but no insulation (must get round to that...)

*Probably* not a lintel at the place you would want to make the hole,
which is presumably at the junction of the party wall and one side of
your 2 foot wall.

I don't think there is a lintel above the door they retrofitted.

Not sure what if any implications there are for putting vent close to
your neighbour.

They don't have any windows or doors nearby, so I think I'm ok?

With a 2 metre straight run I would not worry about pressure drop in
rectangular duct.

Can't see a 6 inch hole having structural implications, especially as it
is probably nearer 4 inches.

Thanks,

On Sun, 30 Jun 2019 09:41:30 +0100, Jeff Layman
wrote:

The OP needs to watch out if the cavity wall insulation is old
polystyrene beads which no longer stick to each other. When the hole
saw is removed the stuff will just pour out (especially if it's a
standard two-storey house and the hole is at the top of the ground
floor). I would advise him to have a vacuum cleaner ready and to shove
the ducting in a soon as possible after the hole saw is pulled out.

No insulation in the cavity but I didn't know that. I'll remember that
if I ever move house and have to do it again.

On Sun, 30 Jun 2019 09:26:12 +0100, ARW
wrote:

If using rectangular ducting then you would be better off with a brick
grille.

I wondered that but what are the chances of the brick being in perfect
alignment to where I want the duct!?

On 08/07/2019 10:43, Stephen wrote:
On Sun, 30 Jun 2019 09:26:12 +0100, ARW
wrote:

If using rectangular ducting then you would be better off with a brick
grille.

I wondered that but what are the chances of the brick being in perfect
alignment to where I want the duct!?


Flexible rectangular ducting for the last bit?

--
Adam