# Ventilation advice needed



## tonyjover (Feb 1, 2008)

Hi all, hopefully someone can give us some good advice because we're really struggling to find a suitable solution here. Apologies in advance for the long post.

We have virtually finished our home cinema (we're in the UK, so that's why I didn't call it a home theater :bigsmile It's small - 2.2m wide, 4.2m long, 2.4m high - and has two 2-seater sofas (or will have when they finally arrive). We've named it "The Cosy Corner"

It's insulated with high-quality sound-deadening material within/behind stud walls and the ceiling and the floor. This also acts as effective heat insulation. So we have effectively ended up with a sealed box which needs adequate ventilation for 4 people (and we won't even go into what happens if someone is a smoker!).

UK homes rarely have HVAC, and ours is no exception.
Above the ceiling is a roof space which has adequately cool air and good ventilation that we can use for ventilating The Cosy Corner.

My initial experiment was to fit two 100mm (4") diameter vents in the ceiling. One of them is above the screen, which is where the roof vents to the eaves above; I thought that would work well as an 'inlet'. It does nothing more than vent into the roof space. The other vent is just in front of the PJ, near the rear of The Cosy Corner, and is connected by a 100mm diameter hose to an inline fan which pulls the stale air into the roof space; I thought this would work well as the 'exhaust'.

The problems we have with the existing setup are:
1. The fan is noisy. Effectively, all we've achieved is a bathroom exhaust.
2. Neither inlet nor exhaust vents are sound deadened, so they're making a large hole in our 'sound-tight' cinema
3. Despite the noise, the system is innefective - the cinema room becomes very stuffy after 30 minutes and we have to open a door. How pointless is that?

So... what I'm thinking of is making two labyrinth baffles - one for each vent - and making the vent areas much bigger. What I don't know is how big the vents should be, plus I have virtually no idea how to design a suitable labyrinth; Google hasn't been a lot of help in this respect.

Can anyone suggest a good place to find a labyrinth design?
How large should the vents be?
Should we be thinking in an entirely different direction?

Thanks in advance
Tony


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## bpape (Sep 14, 2006)

Hi Tony.

Most likely, you'll need at least 6", maybe 8" for the 'exhaust'. I'm also thinking a lot of your problem is simply not enough fan/cfm of air movement. For the labrinth, use MDF or something similar. Keep it around the vent for at least 15' and make sure there are at least 3 90 degree bends in it that are at least 4' apart. Fill the space between the duct and the MDF with insulation.

Don't use any kind of hard ductwork. Use flex-duct if you can get it - otherwise just line the MDF labrinth with duct board. 

Bryan


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## tonyjover (Feb 1, 2008)

bpape said:


> Keep it around the vent for at least 15' and make sure there are at least 3 90 degree bends in it that are at least 4' apart.


Hi Bryan,

Thanks for the response :bigsmile:

I'm a little confused about the labyrinth you describe - do you really mean 15 feet long? If so, wow!

So, if I change the vent to say 8" square, do I then want an 8" x 8" x 15' labyrinth?

Gee...

Thanks again,
Tone


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## Prof. (Oct 20, 2006)

Tony,

I have a similar room situation to yours..
My theatre room is small at 10'6"x15' and is virtually soundproof and airtight..
It did get very stuffy and hot in a short time, so this is what I did...

I originally fitted a 10" diam. exhaust fan in the ceiling tray, that is suspended about 12" below the ceiling..
I then fitted a 10" diam. tube over the back of the fan and put it through a cut out in the ceiling, to exhaust the warm air..
This worked fine until I closed the door, and then the fan slowed considerably, trying to draw air from a sealed room..
So I fit a double sided vent to the bottom of the door, to allow air to be drawn in from outside..
The double sided vent is virtually light proof, plus I have curtain that covers it so you don't even see it ..

Since then, I've now fitted the fan directly onto the ceiling and just have a grill in the ceiling tray where the fan used to be..It works well..It takes the heat from the gear, plus the build up of warm air that accumulates near the ceiling..

If you look around, you should be able to find one of the quieter exhaust fans..

The fan I bought was very quiet and you have to listen for it to even know that it's there..


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## nitrox1 (May 26, 2007)

Hi here is my two cents worth. Try covering back up the holes you made so that you will maintain your sound proofing, see if your builders shop carry any moisture absorbent buckets. Inside the bucket is a material that will take moisture from the air and can be emptied and reused for some time, and it does this silently. Second borrow a large fan and put in your home cinema on the lowest setting and point it at the ceiling. To try this should be inexpensive, but what I think is happening is the heat from 4 people each the equivalent heat of a 100 watt bulb, not to mention the moisture given off by each, plus all the equipment, it's possibly the humidity which is making everyone uncomfortable. If you cannot find the moisture absorbent bucket, freeze as large a piece off ice as you can and put it in plastic and on a tray on the floor and this should help a little with the humidity in the room. Might be worth a try mate. As for smoking, do it outside.
Cheers!


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## bpape (Sep 14, 2006)

The labrinth I was discussing is really 15' long. Imagine going up into the ceiling and immediately turning. Then go 5' and turn 90 degrees. 5 feet in another direction then turn. Repeat one more time. The inside of the box would be 8"x8"x whatever the actual material requirement is.

A ducting system like that works VERY well and does a great job of isolation and allows a strong fan at the far end to really move some air with practically zero audibility. I have people build these all the time and they're all amazed at how well they work.

The trick is to pull air out of the room. If you try to push it in, you're fighting a losing battle. Remember the old high school physics problem about whether it's easier to pull or push a box across concrete? Same principle. We're removing hot air and creating a low pressure area that naturally draws air into the room.

Bryan


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## tonyjover (Feb 1, 2008)

Thanks all 

As soon as I can find the time I'll get up in that roof space and build Bryan's Labyrinth. Hey, sounds like a film title!

I'll let you know how I got on.

Cheers,
Tone


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## MatrixDweller (Jul 24, 2007)

The air up in your unfinished attic is probably stale and would get even hotter than your room on a warm day. You'll need to vent to the exterior. 

For the inlet you could use wide ABS tubing or sheet metal to make two or more 'U' bends then extend it up to the roof and cap it with a proper roof vent to stop water from getting in. Line the interior of the vent with some sound proofing to stop reverberation. You'll get fresher air, but will loose some heat (maybe a good thing?). YOu can also buy duct mufflers (http://www.espenergy.com/duct_muffler.htm).

Do the same for the outlet vent and attach an inline power vent like this one. If you wanted to get fancy you could put an electonic damper on either pipe to seal things up better when not in use.


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## tonyvdb (Sep 5, 2007)

The trick for not only moving air but keeping the noise of the fan out of the equation is to have the fan its self mounted at the far end of the flexible ductwork on the exhaust side this will isolate the noise of the fan. By running the ductwork of the fan outside not in the attic you also eliminate the possibility of condensation buildup in the attic causing mold to grow and other issues.
Fresh air intake should also come from the shady side of the house on the outside this will give you the best cool air movement possible. A 5 inch duct would be more than enough for the exhaust with a minimum 100 CFM fan and a larger duct for the intake.


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## Chicago (Jun 11, 2008)

tonyjover said:


> Hi all, hopefully someone can give us some good advice because we're really struggling to find a suitable solution here. Apologies in advance for the long post.
> 
> We have virtually finished our home cinema (we're in the UK, so that's why I didn't call it a home theater :bigsmile It's small - 2.2m wide, 4.2m long, 2.4m high - and has two 2-seater sofas (or will have when they finally arrive). We've named it "The Cosy Corner"
> 
> ...


 Hi , I know this is little late but just read the thread. I do HVAC for living , What i would suggest is getting a attic fan put into the roof itself, then make a sheet metal box screwed to roof plywood inside attic, insulate the outside of the box, then cut a 10 inch hole in it ,stick a 10 inch round pipe say 6 inches long into the hole, pull 8 inch insulated flex with liner over it tape screw it to pipe, then run the 10 inch flex down to a say 12x12 insulated box in ceiling with a 8 inch hole cut into it,with a 8 inch pipe inside hole. thats more then enough to pull air from the cosy . But i would also cut the top plate of your wall and use the 2x4 bay in the wall as a recycler of air , putting a 6x12 grill very near the floor 6 inches up. This isnt very detailed as i see OP was over 1 month ago and not sure how houses are built over there. If youd like more detailed description PM me or post here again . There are many very cheap and easy options other then this as well . This would virtually eliminate any noise from fan and move quite abit of air while drawing in freash air.


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## bpape (Sep 14, 2006)

From an HVAC standpoint, what you describe would work fine. Unfortunately, it also completely loses any isolation for sound into and out of the room. Using one of the stud cavities as a return would allow a ton of sound to get into and out of the space. 

Also, I would strongly advise that any hvac work for a theater system should be as much flex and duct board as possible with little to no tin involved. The tin can actually amplify mid and high frequency transmission in both directions.

Bryan


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## Chicago (Jun 11, 2008)

bpape said:


> From an HVAC standpoint, what you describe would work fine. Unfortunately, it also completely loses any isolation for sound into and out of the room. Using one of the stud cavities as a return would allow a ton of sound to get into and out of the space.
> 
> Also, I would strongly advise that any hvac work for a theater system should be as much flex and duct board as possible with little to no tin involved. The tin can actually amplify mid and high frequency transmission in both directions.
> 
> Bryan


 As far as the tin goes you could insulate the inside of the 12x12 box with insulboard, And yes i guess if the wall return wasnt placed properly you could lose sound through it ,if it was done in a location where a minimum of sound would escape. Ill be first to admit this is something I have very little knowledge of, so you are more then likely right. How bout if he cut the 12x6 out and slid in pieces of insul board say 3 feet up 3 sides of wall(glued) just another thought. But the movement of air would be more important then the loss of a little sound to me . And like i said , I described breifly my remedy, there are many other ways to do this, But i would definitley get the fan out of the room as far away as possible, Eventually the fan will become loud and need replaced , If in attic attached to roof with say 20 feet or more of inusl flex attached youd never even hear it . 
Well good luck anyways. P.S. Id also have the fan on a switch and not on a thermo switch .


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## tonyvdb (Sep 5, 2007)

I agree with Chicago on this one as i stated in my earlier post the fan needs to be on the far end of the flexible duct.
I also work in the HVAC industry (20 years) and know what will work and what wont. 
The fan can either be placed on the supply duct or exhaust duct but the ductwork that is not forced air needs to be twice the size as the one with the fan to allow for proper air exchange.
Like Chicago mentioned insulation around the outside of the ductwork would virtually eliminate all noise transfer into the attic at least anything that could be heard outside or in other rooms. You can buy pre insulated flex duct from most home renovation stores.


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