The basement and the main floor are on the same system. I wanted to put the theater on its own zone, but the theater area is currently fed from a main branch that also feed a number of other basement and first floor registers, some of which are directly above the theater room. Worse yet, there is rigid metal duct run in the right-side soffit (along with a gas line, a drain line, and some water supply pipes).
Issue 1: Zoning system for theater
I thought that maybe a home run could be added from the main HVAC plenum to the theater room and then that could be zoned separate from the other branches. I called in a couple HVAC guys for a consult and they both basically said, "no way." The first problem is that the system was installed without zoning in mind, so there is not enough space with the unit to fit a new branch for the theater and also a pressure bypass. To do so, the system would have to be laid on its side and then all the lines (gas, duct, etc.) re-run to the new location. On top of that, feeding a single room off of a 3.5 ton unit would not work because the bypass would have to be absolutely huge and it would probably screw up the system to have that much cold air returning directly to the system. You can get away from this potential problem if you use special dampers that have built in bypasses (think spring loaded doors in part of the butterfly valve so that when pressure is too high, that spring loaded door opens and bleeds pressure to other zones. The problem with this approach is that the spring loaded doors cannot be calibrated, so if they do not bleed enough pressure, you can end up with too much velocity at the registers in the theater, resulting in noise. Also, it really ends up being no different than just running the system for the entire basement and first floors when only needing AC in the theater because there will always be excess pressure to bleed off. If that's the case, then why not just put a secondary t-stat and control in the theater and use that when using the theater. The rest of the basement and 1st floor will be over cooled, which is wasteful, but I'm not sure there is a feasible alternative. The cost to just lay the unit on its side and re-run lines was around $6k, so that's not going to happen. So right now, I'm planning on just going with the secondary t-stat and controller in the theater. Anyone have comments/feedback on this idea? I know its a compromise, but it may be the best possible solution (and on the bright side, probably the cheapest).
Issue 2: Rigid duct in the theater:
This one is hard to explain in words, but I'll give it a shot. Here is the rigid duct in the chase:
The HVAC guys didn't want to only run flexible duct because of pressure drop issues. I looked on this site and it appears to be a fairly contentious issue. I'm thinking I can probably take the rigid duct out of the chase, turn it 90 degrees from where it is now and run it between the joists just in front of the wall (outside the theater) that I will build to enclose the theater. I should be able to then re-run two legs totally outside the theater. The two legs that feed the 1st floor directly above the theater can be run with flexible duct, and enter the theater right above the door in the back of the room and follow the chase around the perimeter of the room before exiting the soundproof shell in the appropriate locations. The theater will have two 6in supplies and they can enter off the new rigid duct along the right side chase with one branch then moving to the left side chase near the front of the room by running between the joists. The other potential plan for the theater supplies is to run a much smaller rigid duct in the right side soffit near the right side wall and under the gas and water lines. I would then build the soundproof shell inside of the metal duct and water/gas/drain lines. This means the chase would be split in half with 1/2 being inside the shell and 1/2 being outside the shell. I think this is probably the best plan because I would probably have to do something similar for the gas/water/drain lines anyway.
In this pic you can see three of the existing branches travelling from the metal duct in the right side chase to the left side wall where two go up to the first floor and one feeds the theater room.
In this pic you can see two runs from the metal duct that are in the defined theater area. One of these feeds the basement on the other side of the room and the other feeds the first floor. These are the two runs I think I can keep completely out of the theater room by turning the metal duct 90 deg and running it between the joists along the outside of the back theater room wall.
I should also mention that one of my goals is to decrease the width of the chase. Its currently 24in wide and I think it looks disproportional to the room. So everything is going to get more cramped in the chase (especially when I need space to install recessed lights)
In the above pic, where the drywall is missing defines the dimensions of the theater room. The metal duct comes from room behind the door on the right side of the picture. So the metal duct turns right 90 degrees. I am thinking about running the duct straight (remove the 90 deg turn) but have it move up so that it is between the joists. It would be between the first set of joists where the drywall begins in the pic above.
This is clear in my head because I have walked through the room and I wrote the description, but it may be unclear to others. Please let me know if this is confusing and I will try to clarify with additional pictures and text. If it is clear, I'm looking for feedback. Is this the best approach given my constraints, or is there a better way to do this? Also, If I go with a small rigid metal duct for the two 6in feeds to the theater, what dimensions would suffice? I know that for flexible duct, you usually go with an 8in for two 6s, but is it generally the same for rigid, or can you get away with less because it is more efficient?
I have an idea for a return which I will discuss in a subsequent post.
By the way, is this seating distance too immersive?