Hot or Not: Rate My HVAC Design

Hey Guys... I'm getting ready to start looking for quotes for the HVAC system in our studio we plan to begin building in January. Here is the design we have planned. I know there are some experts on this forum, does anyone see any huge flaws? Attached is the design. Summary: - Remove all existing, change ducts to galvanized w/ fiberglass lining - Increase duct size - 26"x16" main, 12"x12" live room/iso booth - Stagger ducts so 2 supplies are not directly across from each other on main supply - Use flex duct for connections from damper off main supply to diffuser - Main return duct - fiberglass lined galvanized - Cut 24"x30" hole in top of main return with batt insulation on ceiling above opening - Added in a supply for back entry/hall to account for excess air in the system - Use canvas connectors to attach ducts to rooftop unit - Possibly remount the roof furnace on Isolation Pads - Each return duct will be venting into the cavity between the existing ceiling and the isolation ceiling. So, with this plan, there wouldn't be a continuous duct, it would just be room to room flow. Thank you for any views/responses!

Here is my other thread on studio layout (if you're looking for more info on my project): viewtopic.php?f=1&t=14889

so you're planning on using the air space in-between the isolation ceiling and existing ceiling for a return duct? a couple of thoughts - 1. isolation - your baffle box will effectively vent into that space? 2. is that within code? i would be surprised if it was especially if you consider a fire in that space the smoke and other gases would quickly permeate your ventilation system. you should consider proper ducting for the returns.

gullfo wrote:

so you're planning on using the air space in-between the isolation ceiling and existing ceiling for a return duct? a couple of thoughts - 1. isolation - your baffle box will effectively vent into that space? 2. is that within code? i would be surprised if it was especially if you consider a fire in that space the smoke and other gases would quickly permeate your ventilation system. you should consider proper ducting for the returns.

Thanks for the reply, Glenn. For returns, this plan calls for a return grille in the ceiling followed by an L-shaped duct that would just vent into the space between the existing and isolation ceilings. Then there would be room-to-room exchange in that cavity, so the returns wouldn't really be isolated from room to room. We also didn't figure in for any baffle boxes. If we decide to use a typical fiberglass-lined return duct system, do we need baffle boxes? We're not sure how to determine what size we'd need or the effect that they'll have on the system load so we can compensate with correct duct sizing. Is there any way to isolate without using proper ducting? I was thinking that the baffle boxes are mainly used on supply ducts, are they commonly used on returns as well?

gullfo wrote:

interesting question... i think you need to have a silencer for each supply or return you have into the room otherwise what keeps the sound from simply going up a 12" hole and into the lightwight (by comparison to the wall or ceiling mass) duct?... or can you simply build a massive MDF box around it?

(Quoted from another thread) Makes sense, I will have my carpenter design some silencers, and my HVAC designer can add them into the design along with the complete return ductwork.

swiftschool wrote:

Is there any way to isolate without using proper ducting?

you need to isolate the returns and the supplies to be fully effective. the ducting is required for proper system efficiency and safety.

My rating is "Not". This design has more flaws than I can see, the main one being the connected trunk and arms to the rooms effectively building a bridge for sound to jump into one room from another room...just like a residential system would do. The other is the ducting is too small so when it reduces and increases the air speed, noise is introduced. Same goes for the returns...too small based on what I can see. Those isolation boxes you require should not be left in the hands of a carpenter unless he has built a few before and knows what it is you guys are trying to attempt with this decoupling, sound isolation item. Tried and true works best so no body has to re-invent the wheel :) All the following links are located on John's forum site and give the answer for the questions you may need to have answered about HVAC baffles, plenums, etc. viewtopic.php?f=2&t=10303&start=0 viewtopic.php?f=1&t=11542&start=0 viewtopic.php?f=2&t=9990&start=0 viewtopic.php?f=2&t=11410&start=0