Ventilation Fan Placement

[Johnbroadb]

Hi,

I have been reading thread after thread on Ventilation and silencer boxes, I'm feeling pretty good with how it all works, I just have few questions that i can't seem to find the answer for.

Am i correct in saying i would have an air out line with a silencer box in a soffit which is attached to my inner leaf framing, the silencer box penetrates the inner leaf then the ducting is run in-between the leaves and penetrates the outer leaf (preferably not right next to the inner leaf penetration)?

I was planning to use an inline fan with the right specs i need, where do i put the fan? does it run inside the leaves? otherwise it would either be in the room or outside in the weather?

For the air intake line is the silencer box also inside, so its the last thing the air moves through before entering the room?

Thanks for your help.

John

[Soundman2020]

Am i correct in saying i would have an air out line with a silencer box in a soffit which is attached to my inner leaf framing, the silencer box penetrates the inner leaf then the ducting is run in-between the leaves and penetrates the outer leaf

You also need a silencer box at the point where the duct penetrates the outer leaf. One box for each penetration.

If you don't need very high levels of isolation then you can design a silencer box that has some type of thick wooden "sleeve" that goes through both leaves but without touching them mechanically: decoupled with highly flexible caulk. But if you need good isolation, the you need a box on each penetration.

I was planning to use an inline fan with the right specs i need, where do i put the fan? does it run inside the leaves? otherwise it would either be in the room or outside in the weather?

If you have a fan inside the wall cavity, you have no access to it! You can't get it to for cleaning, maintenance, repair or replacement. You'd have to break down your studio wall to get to it...

Of course, you don't want to have fans inside your room, so that leaves you with the only other option: the fan(s) must go outside. So you need an exterior fan, not inline. Something like this:

Fantech-exterior-exhaust-fan.jpg

Fantech makes some good ones, such as the EWE152 and EWE 154, and the RVF line.

For the air intake line is the silencer box also inside, so its the last thing the air moves through before entering the room?

Same rule as for the exhaust duct: one silencer box per leaf penetration, if you want high levels of isolation. If your needs are not so extreme, then you can make one box with a sleeve that goes through both leaves, and is decoupled from them.


- Stuart -

[Johnbroadb]

Its making great sense now, thank you so much for your input!
Can i have the silencer box for my outer leaf penetration in the cavity attached to the outer leaf wall? So i would have a silencer box on the inside penetrating the inner leaf then another box inside the cavity penetrating the outer leaf.

I understand this would mean the space between the leaves would need to be sufficient enough to house a silencer box.

Thanks heaps!

[Johnbroadb]

I was going to ask as well, is it prudent to have a supply fan as well as an exhaust fan? or will the negative pressure in the room be enough to draw the fresh air in?

[Soundman2020]

Can i have the silencer box for my outer leaf penetration in the cavity attached to the outer leaf wall? So i would have a silencer box on the inside penetrating the inner leaf then another box inside the cavity penetrating the outer leaf.

You sure can! I often do it that way. In fact, I often put BOTH boxes inside the cavity, so there's nothing inside the rooms or outside the building at all! Keeps it clean, visually. You can link the two boxes with simple flex duct.

Once again, this "two boxes per duct" approach is only needed if you have a need for fairly high degree of isolation. If your needs are a bit more modest, then you can have one single box on each duct, with penetrations through both leaves using solid "sleeves" that are carefully decoupled at the point where they pass through each leaf.

I understand this would mean the space between the leaves would need to be sufficient enough to house a silencer box

Yup!

is it prudent to have a supply fan as well as an exhaust fan?

You can do that, but then you have to carefully balance the flow from both fans to be the same. If not, then one fan tries to "drive" the other. Since the room is basically a sealed box, if one fan is running faster than the other, moving more air, then that additional air pressure forces the other fan to speed up as well, which isn't good for the motor, bearings or air noise. As long as you can balance the two air flows well, then you can do it.

or will the negative pressure in the room be enough to draw the fresh air in?

It will be enough. However, there is a good point to be made for having only one fan but on the inlet side, creating a positive pressure inside the room, that "pushes out" the stale air through the exhaust duct. Having positive pressure inside the room does prevent air leaking in through any tiny gaps that you might have missed when you sealed up the room... And it does tend to keep your door closed a bit more tightly, up against the seals (but not a huge amount!).

In other words, use just one fan, not two, and there's a slight advantage to putting it on the inlet, but there's also no problem at all with putting it on the exhaust.


- Stuart -