Post your Dead Vent and HVAC Pics - Page 4

Yes you would need a flow hood to do that. I have used one a few times. 2500 dollars new so I just rented

When building a deadvent like this, what keeps the sound from traveling out of the vent and down the air cavity between the studs in a double stud wall? Since the vent doesn't trap the sound waves, isn't it basically like just putting a big whole in the wall you just tried to sound proof? Sorry if I missed the answer to this, I looked through the whole thread but didn't see it.

Attachment 189849

It's the 6" PVC pipe. Wrap with pipe wrap or MLV. Quite massive and damped when done.

Ahh, ok, didn't realize what "pipe wrap" was. Thanks for your help.

Sure thing. If you want to review a plan, lemme know.

How many of these would you need per room? Is it a function of cubic volume of the room?

There could be 1-2 supplies, and generally one return. My room is 15 x 23 and has one supply, one return, both Dead Vents.

Alternately, you might use the theater room's soffits like this:

I've seen that diagram before but it doesn't look like it would provide near the level of sound reduction that the previous diagrams show. You have a very small area surrounding the pipe and not much room for insulation.

The Dead Vent is short but very fat, allowing for a lot on insulation around the flex. The soffit muffler (above) is narrower, but it's also 15' long. It's all about the interior volume

Ted,

If the ceiling above the soffit is DD+GG, is it okay to penetrate the dead vent soffit to install screen wash lights? The integrity of the room isolation should still be maintained - just wondering if that would reduce the effectivness of the dead vent if there are can lights installed in that same soffit.

Hi Brian,

The "Dead Vent" is a stand-alone structure in an adjacent room or perhaps behind the screen wall. Looks like a phone booth.

I believe you're referring to a soffit that is being used as a muffler. THis Soffit Muffler can't have additional holes in it. We want the sound level to drop for every foot of travel through the muffler. If we have holes along the way, new sound is constantly re-introduced into the muffler, defeating its function.

You wwould have to use surface mounted pucks or build backer boxes for each can light or build a split soffit that is 1/2 muffler and 1/2 lighting.

Make sense?

That makes perfect sense. Thanks for the quick response!

Glad to try and help a little.

Here's mine. I decided to make curved soffits instead. I used a Fantech FR150 and initially, a rotary dimmer switch for speed control. Unfortunately, a dimmer switch is not made for fan control, and made the motor hum loudly when the speed was set anywhere lower than full.

I thought I was going to have to buy a fan with a lower CFM output, such as the Fantech FR100, but I swapped out the dimmer for a proper 3 step speed control (Lutron S2-LFSQH) after reading that's how someone else solved their hum problem. I'll start a thread before too long with my HT progress.

John

I have not come across this and would like to know more about this. I myself have 4 fans controlled by ceiling fan speed conrols. I have not noticed any humm.

Darn nice soffit framing!

Thanks, Ted. All that insulation really helps! With regard to the rotary dimmer and motor hum: I think it has to do with capacitors, but I'm not sure. I suspect that the controls you are using are proper speed controls designed for fan use, probably with built in circuitry designed for the job. Be glad you don't have that problem- that motor hum can bring a dead vent to life, in a bad way!

Incidentally, I also read that a rotary dimmer can cause the fan to burn out if turned down too much- the fan will stop spinning but current still goes to the motor coils. I noticed this while playing around with the dimmer I was using. Fortunately, I immediately dialed it back up or shut it off and had no problems.

John

I'm using a standard Lowes Ceiling Fan variable speed controller. Under $25 as I recall. The only issue I've been aware of is to not try and use a lighting dimmer switch. Needs to me a motor controller, which is a ceiling fan.

Yep, that's what I was doing. I initially bought the dimmer switch, thinking that I could dial in just the right fan speed, something you can't do as well with a stepped adjustable speed controller.

However, I'll gladly trade a little loss of speed control for a big loss in noise (motor hum gone) when using a real controller like the ones you are using and the one I'm now using.

John

Ted,

Probably a dumb question, but here goes. Does a dead vent that transfers the air from one room to the next considered a return? I'm assuming it is and that it eventually makes it's way to adjoing rooms return.

If you have a fan on the supply, does it reduce the need requiring two supplies to a room 17' x 25'.

If there is a cold air return near by, does it make sense just to go through the dead vent and then into the cold air return?

Good questions.


An actual "return" feeds back directly to the furnace. This keeps the system balanced. Just as much air leaving the furnace as is being returned.


Not really. The booster fans simply help overcome the resistance from the longer run and the non-smooth coiled interior of the flex.


Yes. No need to install a special run all the way back to the furnace. Just tap into the nearest return.

Ted,

Thanks so much. For further clarification
1) Can a dead vent that moves air to an adjoiningg room replace a return or is a return recommended in addition to a dead vent?
2) Are there any advantages/disadvantages to connecting the dead vent to an existing return? I have a room above that would also be sharing that same return and I just want to make sure sound leakage doesn't become a problem if I have the option to push the air into an adjoining room. I also don't want to push hot or cold air up to the floor above. I'm ok if some sound leakage enters the basement area.

Thanks as always.

Well the room itself requires air in and out. If both are simple exchanging air with the rest of the basement, that's fine. Or both can be directly connected to the main HVAC. I would not suggest splitting them so that the supply to the room is from the HVAC system, while the return is simply to a nearby room. This can throw the air handling calculations off.


No worries other than the realization that the DV or soffit mufflers will increase the length and air resistance on that leg. This may require the booster fan.

Given that the return is just above where my dead vent would be and then that run is inbetween joists and only about 4' to the main duct...do you think I'll even need the booster fan (Fantech)?

Also, in this diagram (not sure if this is yours or not), I don't see a conversion of 6" > 12" and then back again. Is that no longer recommended?


Also, why the 6" gap at the top of the dead vent?

Perhaps no need for the fan


That is our diagram, and the recommended design has changed.


To allow you to stand it up when completed

Ted,

So this begs my next stupid question:
Is the large enclosure designed to muffle the Fantech FG6XL Fan or the noise that enters the register from the theater room? I'm guessing it's for both?

Assuming I'm doing new construction, could I just bring the dead vent framing all the way to my joists and just put 2 layers of plywood with GG in-between in order to sound proof the area above the dead vent frame?

Also, it appears that we don't need to use insulated 6" flex duct...correct?

I see the one dimension recommendation is 24" at the base, but what is the other recommendation? 24" x 24" or can it be narrower with similar results?

Yes, both

Yes you could. I might avoid contact with the joists if that's practical

Correct

24" x 24" is really a minimum. More is better. We want the insulation volume.

i'm in the process of building my DV and have a question about the 6" > 12" conversion (even though it's no longer in the recommendation). I have installed a 25' 8" flex insulated duct between the DV location in the soffit of the theatre and the adjacent room. I am about to order a fan tech inline fan but I'm trying to determine whether there is any benefit in going with an FG6XL ( 8" down to 6" ) or staying at 8" with a FG8 or 8xl.

any help would be appreciated.

Sorry to resurrect an old thread.

David

Ted,

Thanks for your excellent advice. I have two questions:

- Is there any reason why I couldn't use just one (bigger?) deadvent for both inlet and return? I would then use two seperate flex ducts within one deadvent casing. I would space the intake and outlet apart on the outside as well as the inside with plain duct piping.

- Can the intake vent be rectangular, or is circular the prefered shape? Isn't a slot intake better in terms of sound leakage?

Thanks,

Peter

Is there any need for a fan access panel?

Ted designed a mockup dead vent layout for me that will contain both an inlet and return. Total external dimensions are 9' high, 1.5' wide and 3' deep. It's essentially one DD/GG framed box with one complete horizontal and 2 partial vertical DD/GG dividers in the box that you weave the flex-duct around. Plan is to pull air out of the theater with a register near the projector mount, and feed cooler air from the basement floor level into the theater. I'll also have a minisplit for additional cooling, but I wanted a vent more for air exchange.