Do I need a fan on the outlet?

[Melv]

Hello. I have built a band practice/ recording room in my garden. It is 3.3 metres x 4.4 metres and a floor to ceiling height of 2metres. I have created an air intake hole at one end and have made and fitted a baffle box with an inline fan pulling fresh, filtered, outside air into the room. I have also made a hole at the opposite side of the room for the outlet. I am in the process of building the baffle box for this. My main question is...Do I need a fan on the outlet/exhaust? Or, will the build up of pressure force the air out. Any help would be appreciated.

[gullfo]

since you're doing all that work, i'd say install the exhaust fan to ensure steady flow. consider things like moisture (humidity) and seasonal temperature impact on your outdoor ventilation. high humidity can cause mold in the ducts and baffle boxes.

[Melv]

Thanks for your reply Glenn. Yes, some good points there. Looks like a fan it is then.
Hmmm here comes a whole lot of questions and a headache trying to find out spec of the fan.
This building a studio malarky is a science in itself.
So, new main question... Would the exhaust fan need to equal the extraction rate of the inlet?
Or would it need to be more, or less. Sorry I'm a bit stumped here.

[gullfo]

make them the same, or worst case the intake slightly more (e.g. 50cfm out, 60cfm in) may be ok but it would be better to get them the same as duct and plenum and silencer frictions will play into it and if you install a damper on the vents, you can shift the balance if needed.

[Paulus87]

In my opinion I would try out the whole system without a fan at the outlet at first. The fan pushing air into the space will pressurise the room and the air will be drawn out of your exhaust passively anyway.

[Melv]

In my opinion I would try out the whole system without a fan at the outlet at first. The fan pushing air into the space will pressurise the room and the air will be drawn out of your exhaust passively anyway.

Thanks Paul, yeah that's what I was thinking too, but Glenn has certainly put some valid points about condensation etc. Decision time I think.

[Melv]

make them the same, or worst case the intake slightly more (e.g. 50cfm out, 60cfm in) may be ok but it would be better to get them the same as duct and plenum and silencer frictions will play into it and if you install a damper on the vents, you can shift the balance if needed.

Thanks Glenn, that's a massive help and has saved me a lot of hastle. I can easily buy the same fan as the inlet and fit that to the exhaust baffle box. Sorry I don't know what you mean by a damper, but I guess it is some kind a device/flap to slow flow down if needed. However I am going to fit some kind of a potentiometer (dimmer switch) to control the fan speeds when needed, so that should help me to get a good balance. Does this sound a good idea?

Actually, no, that is a bad idea, as I have just spoke to my electrician and you can not safely run an inline fan from a dimmer switch. However, my fan does have two speeds so I can can control it that way up, all be it not to the extent I would like to.

[John Steel]

Hello & howdo' Melv?
It's worth mentioning that it is possible to buy remote speed controllers for inline fans. I ordered a Soler & Palau 'Ecowatt' inline fan with a specified speed controller (which actually does look like a dimmer switch btw) but there are lots of different options. Just make sure the controller is compatible with the fan before parting with cash. Good luck & best wishes, John.

[Melv]

Hello & howdo' Melv?
It's worth mentioning that it is possible to buy remote speed controllers for inline fans. I ordered a PalauSoler & 'Ecowatt' inline fan with a specified speed controller (which actually does look like a dimmer switch btw) but there are lots of different options. Just make sure the controller is compatible with the fan before parting with cash. Good luck & best wishes, John.

Hey nice 1 John. Very well thank you and thanks for the info. I will definitely look into speed controllers then. If I can't get one for my fan's spec then at least I still have the Hi & Low switch option, therefore still maintaining a degree of control.