HVAC Redo/Retrofit

When I did my room the first time, I tied the return (for the theater room) into an existing return, which was at the front of the room. There is a room (the family room) on the other side of my screen wall but it is at grade level. My theater room is in a basement with the floor about 4 FT below grade. The return that I had tied into was a 'between the studs' of the interior wall between the rooms. The way I tied into it was to just cut a hole in the backside of the sheet metal to allow the opening through the wall down to a vent at the floor of the theater room. This made a perfect path for sound to travel out of the theater room to the family room (bad planning) And, I also put the return at the screen wall side of the room, which I have since learned is a big no-no. I have decided to go back and relocate the return for this room. I want to seal up this return from the room and put one near the rear of the room. More on that later. . .

The picture below shows what I'm talking about. My question is if there is anything I should do to help minimize sound leaking into the return. I have plenty of Linacoustic. Should I fil the channel between the studs with Linacoustic or just the fluffy pink/white insulation? FYI, the door to the right is actually the access to the furnace. My plan was to just get another piece of sheet metal and duct tape it over the hole. Maybe I should put some Linacoustic inside of the return. Any help would be appreciated.

Edit: I'll attach the photo just in case someone wants to zoom in. 2012-11-11_14-30-56_513.jpg 1106k .jpg file

A head-slapping moment last night as I investigated further. This in-wall return also goes up to the room above the theater room (living room). No wonder it's so loud up there when I'm watching a movie. Plus all the other reasons like can lights and the fact that it is directly over the room.

So now I'm thinking I need to put Linacoustic in the whole return. That gets installed stiff side to the airflow, right?

. . . . anyone?

Got it, thanks, Big! That does make a pretty substantial difference in the cross-sectional area of the in-wall return. It goes from about 50 square inches (without Linacoustic) to less than 20 square inches with 1" Linacoustic. That's huge! Is there any way to determine if that would be detrimental? I've seen the charts that are on the Plains Theater Build that may help.

I wonder if it would be worth just putting a piece of Linacoustic on the back side of the return vent space. I'm just trying to minimize noise getting into the HVAC. Any other thoughts?

since I basically have a wall thickness between the theater room and the back of the return I'm sure I'm better off than if the return was right in the actual wall of the theater.
Edited by angryht - 11/14/12 at 3:31pm

Well, that's what I decided to do. One piece of Linacoustic placed on the inside of the return (opposite the vent/diffusor). That should help to absorb some sound from the adjacent rooms.

Now, is there anything special I should do within the theater room wall in terms of insulation? I was thinking of just installing batts of fiberglass insulation. To review, this is an interior wall that is adjacent to the interior wall for the next room. Basically, the sheet metal for the in-wall return (back-side) is exposed to the inside of the theater room wall. My question is whether or not it would be recommended to install something different in that cavity like roxul or some other more dense/sound effective material since the return is on the other side of the wall. My repair of the sheet metal that had a hole in it was just duct tape (the 'foil' type tape with the peel-off backing. Any input would be appreciated.

I guess I'll just put standard wall fiberglass insulation in the cavity. Looks like R13 is the way to go???


Would I gain anything by stuffing something like an R25 into the wall (8" thick) or would that just transmit sound through to the return on the other side?

I just went with some R19 that I had left over from the joists.

Okay, that's done. Now I've moved on to the next thing which is to move the supply closer to the front of the room. The register was almost directly over the seating position. I cut a hole in the drywall ceiling to get access to the joist cavity. My plan was to just move the register a about 5 feet towards the front. However, I realize now that will place it closer to the main trunk - which may cause more flanking noise into the rest of the house. I'm guessing there is not much I can do about that. I'm using 6" flex and working in the truss cavity, how do I introduce 90's (or snake it) to minimize the straight path? Do I put in something like a one-by's as a block on the top and bottom? Is there an easier way?

What about registers (vents)? Are there prefered sizes or types?

Sorry about not having a drawing. Actually, I made one on a different thread with a hushbox question. Ill grab that.

The joists run front to back.

The trunk is just outside the theater room but I would not be able to run the duct through the joists. I'd need to build a soffit, which I'd like to avoid. What about just having the vent at the right wall? It would be just next to the main trunk but I suppose I could do a dead vent there or in that adjacent room.

No plans for a false wall at this time. The upper right vent is probably the way to go. I'm thinkinig of putting a return on the wall above the equipment closet. Another dead vent? Then I could run a duct to the hushbox.

I'm thinking about getting rid if the can lights (yellow circles on the drawing) and maybe getting some sconces? I don't think I can do the clips/channel. Any other suggestions?

I would close off the current supply line (coming from the front of the room), since it goes directly into the trunk. Then run a deadvent from the supply that is accessible from adjacent room. The return would rerouted to the right along the back wall and out to the adjacent room. That is not shown on the diagram. I thought tying into a return trunk may not be necessary. I was hoping to reduce flanking through the HVAC.

My thought on the removal of the can lights was to further reduce flanking through the ceiling. I thought that would be simpler than encasing them in MDF.

I wish I could do the clips but I don't want to remove the entire ceiling. I guess I was hoping these measures would improve things quite a bit. I don't think I can completely decouple yet. Am I wasting my efforts with this approach?

This is the revised drawing.

Here's a picture of the existing soffit with the flex duct that I am considering removing.


This a pic of the adjacent room with the furnace.


Sorry for the poor quality pictures and the mess. The picture showing the water heater has the furnace behind it and the supply trunk is in the front and the supply trunk behind.

The picture inside the theater room shows the soffits and the flex duct pulled out (which I am wondering if I should cap). Again, sorry for the quality.
Edited by angryht - 11/26/12 at 7:17am

If I tie into the supply trunk in the adjacent room, I'll be able to introduce some 90-degree bends between the penetration into the room and the supply trunk. That'll be somewhat advantageous, right? Even if I don't do a full dead vent. And speaking of penetrations, what is prefered? I've seen many drawings from Ted White/SPC that show a 6" PVC running through the wall. I guess it seems straight forward enough to just put a steel band around that to attach the flex duct outside but what about attaching the diffuser/register to the inside room. Use some sort of blockout? Anyone have a photo or detail? And I'm still wondering about the actual register itself. Rectilinear architectural? Do they have a way to close? Can I get these at big box store or are they specialty?

Edit: One more question. What do most people use to hang flex duct? Pipe hangers? hooks?
Edited by angryht - 11/26/12 at 9:15am

I was doing a little more research on this and it looks like the solution is simpler than I thought. I don't even need to tie into the central air at all. I can just put in a fan to pull out the hot air from the theater room and exchange it with the air in the adjacent room. That would eliminate the need to tap into the supply. I could just run a flex duct out of the room and have it attached to an in-line duct fan to pull air out of the theater room. Then I could have another flex duct connected to a separate in-line fan as a supply, if needed? And if I need to for the summer, get a dehumidifier? I'm still unsure about making the penetrations into the theater room through the walls. Should I just use the typical duct work connector?



or is it better to get some 6" PVC?

and how do I terminate it so it does not slip through the wall? Just connect flex duct to both sides? Any pictures or diagrams would be helpful. I am looking at Ted's famous dead vent drawing and trying to understand the 6" PVC and how it's secured within the wall. It looks like the dead vent is pulling the air out of the theater room from below, near the floor. Isn't preferred to pull the hot air out from the top of the room? Since my room is so small (about 800 CF) I should be able to use a standard in-line duct fan.

Thoughts?

Thanks so much for the link and the knowledge! Black Cat's post is a great resource for the testing. My take is that it shows that there needs to be a fan pushing the air back into the room, especially if there is such a powerful fan pulling out the air like Black Cat's Panasonic fan with 340 CFM - used by many others around here as well. You've got the Pany 440, right?

Below is a better diagram showing my room dimensions as well as the soffit:





When I do a little bit more accurate calculations I get about 785 CF. At 6 exchanges per hour, that gets me to 78.5 CFM required, right. (785 CF) * (6 exchanges/hr) / 60 min/hr) = 78.5 CFM.

I was only planning on using 6" flex duct and according to the chart on your build (fantastic resource by the way - thanks!) a 6" flex duct has a capacity of 75 CFM. I'm kind of thinking that with the couch and other items in the room I might actually be pretty close to the 750 CF (for the 75 CFM). I am also considering just using the 6" inline duct fans. They are rated at 160 CFM 'free air'. My thought was to have a total of 2 fans, one attached to a return (exhaust) to pull air out of the room and one attached to a supply. The space adjacent to the theater room (with the water heater and furnace) has a 6" duct that supplies outside air to that room. I added that to help 'feed' the furnace during the winter when I built the room and reduced the size of the furnace room. I thought if I could exhaust the theater room into that space and bring in some cool air from that space (say from along the floor of the adjacent room) I'd be good to go. I haven't built a hush box yet (I had sort of one before but it's gone now) but I was hoping to build one and just allow the air in the room go through it and out the exhaust along the back wall and out through the top of the equipment closet.


Hey, I just thought of an alternative to buying a 10' section of 6" diameter PVC and cutting it up. From time to time my work requires testing concrete and the molds they use are 6" diameter by 12" tall cylinders, cut the bottom out and attach the flex duct (as long as the outside diameter is about right). I bet I could get some of those. They look like this:


I'm not sure if they are PVC or a different poly. They would have them at local geotechnical/material testing firms. They even have a lip to hold it on the inside of the room. I'm still unsure how the register/vent gets attached to the theater room side.

http://www.avsforum.com/t/1256990/post-your-dead-vent-and-hvac-pics/30

Just putting in another good link for a resource.