8"(200mm) Y splitter to 8" to 4" reducers?

As above, I don't really want to core drill an 8" hole in my outside wall but quit happy to pop in a couple of 4" holes if it doesn't cause any problem with the airflow. The plan is to have my filter/fan (both are 8"/200mm) then have a Y splitter which then reduces ideally down to 4" or 100mm each and has them vent outside or maybe vent on back into the house so I can check for smells and also have a little 'free heat'.

Just wanted to know if the airflow will still be the same or similar to having a straight 8"pipe outside the house. Drill bits are not cheap and don't really want a hole that big sticking out of the house.

Cheers

Two 4” holes will not be the same size as an 8”, I think it would be more like 4x4” holes. Don’t quote me on that lol

It will reduce the airflow alittle

Brettman said:

Two 4” holes will not be the same size as an 8”, I think it would be more like 4x4” holes. Don’t quote me on that lol

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This^^^

Area of a circle = πr²

For the one 8" duct:
1 * π * 4² = 50.27in²

For the two 4" ducts:
2 * π * 2² = 25.13in²

If you did four 4" ducts:
4 * π * 2² = 50.27in²

Like @Brettman mentioned, it's more like four 4" holes. However, you'll also be increasing the headloss with the splitters. So, in practice four 4" ducts will still have a lower performance than one 8" duct.

Meh, sounds like I will have to just do 8" hole then. Bummer.

Cheers chaps

Couldnt you use an 8" to 6" reducer to minimize your hole? It would help without loosing to cfm..

Two 6" would be better that two 4" definitely

Yeah I'd just get an 8 cut in. Why do you need to go thru a foundation and not the rim joist?

I think just doing a 8"hole will be best me thinks.

waring192 said:

I think just doing a 8"hole will be best me thinks.

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How big is your room?

bk78 said:

How big is your room?

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Its around 3.8m x 4m x 2.2

waring192 said:

Its around 3.8m x 4m x 2.2

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at least 8". Might as well do an 8" hole since two 4" holes will be at least 8" s wide anyway, unless their overlapped. You may also want an intake at least a few feet away.

There are rectangular ducting options too. And all the adapters you would need. Would look better on the side of a house to have a low profile square vent with louvers, than some big bulky 8" roof top looking vent..

farmerfischer said:

Couldnt you use an 8" to 6" reducer to minimize your hole? It would help without loosing to cfm..

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I second this! I have the same and it doesn’t reduce airflow by that much

Plus If the extract is on a controller it won’t matter as much anyway as this will reduce fan speed and lower the airflow, mine rarely go above 20%

Are you drilling a cinder block foundation or a wood rim joist?

nxsov180db said:

Are you drilling a cinder block foundation or a wood rim joist?

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Not looks yet but sounds like its going to be a cinder block.