HVAC - Air Return question

At some point it dawned on me that a sealed room required oxygen and not just a wall unit recycling an ever decreasing amount of air :idea: Yes I know sometimes the bleeding obvious just isn't :) My construction takes up 1 room and a garage under the main roof. My existing house AC needed beefing up anyway so I got the local guy in to advise. The air in the studio coming in needs to be vented back out (now obvious) so that it can be returned to the main intake. His suggestion was to vent it back into another room. I have looked at a few HVAC posts and most are concerned with noise where the air is pumped into the studio room and talk about silencers etc. My concern is that even with 90 degree bends this would still be a source where noise could enter the studio as well as probably transmitting noise into another room of the house. My question - is there another alternative or is there a way to minimise/eliminate this possibility? If this has been discussed before I apologise and just point me to that post. Thanks

I think your choices are the following: 1. Vent the return directly to the main return line and install a silencing baffle in-line. 2. Disconnect your studio from the main AC and use a seperate system (and seperate fresh air source) 3. Vent into a small-ish second room (which will also need to be built to a failrly high STC) which contains a direct line to the retrun. In this case the room is acting like a plenum chamber which will reduce sound transmission into (and from) the rest of the system. I'm not sure what the building code would say about this approach...but if your AC guy suggested it maybe he knows. I'm not sure if you saw my thread from a few weeks ago....it was regarding HVAC return noise: http://www.johnlsayers.com/phpBB2/viewtopic.php?t=8481 Cheers Kris

renegade, I've done a bit of posting back and forth with Rod on HVAC topic on my thread starting on this page: http://www.johnlsayers.com/phpBB2/viewt ... &start=465 You may want for Rod to chime in if I recommend something wrong, but I want to take a crack at it just for the exercise... Your Return should not vent into another room, it should tie in to a return duct (plenum) on your existing system. Want to use the same size ducts on return(s) and supply(s) so the pull and push (in CFM and velocity) stays the same. Who knows if the static pressure of venting into another room in house would be able to draw enough air out of return duct from studio room(s). You are going to need fresh air from the outside to go to your room(s), in code (at least in USA) sealed rooms like we build which do not have windows need mechanical ventilation... maybe you do have a window in the room to outside BUT if you don't, recommendation in 15 cfm of fresh air per person. A fresh air duct with fan could be tied into supply. Tied into the return, a fresh air exhaust duct with barometric damper, everything stays balanced. This maybe be the cheapest route which has been suggested to me... and I did fight over the idea. If you current air handler and duct work will allow (cost effectively?) you may want to create zones for your HVAC... one zone for your house and one for your studio. There are many retro fit HVAC zoning kits available online. You can also do a HRV or a ERV, Google search those. Take a look at Sharwards thread, if you can find the page Sharward basically got slammed by a code officer when submitting a plan for permit which did not include fresh air. Sharward is doing HRV. Also you have to make your current HVAC system can handle the new load. According to others cooling is the thing contractors will screw most, heating takes care of itself. I'm going to stop myself here BUT will ask: What is your current HVAC system? Does your heat or cool more in a year? How big is your house in sqft or cubic AND how big is the addition of studio in sqft and cubic? AND OR is your HVAC guy saying your system us big enough to take on additional load. Marc

Thanks for the reply and the references to other posts. There is a wealth of info in those posts and it will take me a considerable amount of time to absorb it all. Correct me if I'm wrong but on the one hand I need a sealed room but at the same time I need an outlet to the outside world for air. The two seem mutually exclusive? The HVAC is being replaced in the entire house and the HVAC guy has taken into account the additional load with the new system and appropriately zoned the new system. I will be talking to him this arvo so I will be asking again why the return can't go straight back to the main return - I'm sure I asked him before and there was apparently a good reason why - I will find out. The HVAC guy has specified that the send & return have to be the same size. But at this point I'm not concerned with noise created by air movement (I hope this won't be a problem) but rather the risk of noise entering & exiting via the return which the HVAC guy plans to return into another large room of the house. Thoughts? Mick PS There seems to be more chance of getting this wrong than right. PPS Apparently there are no stupid questions only stupid people :lol:

Marc put you in some great directions with those links. Yes, absorb much. You will become very knowledgeable in the process. You are wise to take this part of your plan slowly. I spun around in circles for weeks before I came up with something that would pass muster at the city (and I'm glad I did). Even now I'm at that stage in my project and I'm running into snags, but nothing I can't overcome. Good luck. Keep us posted. Ask questions. Use Search feature. Buy Rod's book. Have fun. Make friends. Eat your vegetables. --Keith :mrgreen:

Thanks for that. I have just spoken to the HVAC guy and he said the return can be sent straight back to the main return and not outlet to another room. The only thing is that he has to put in a dampner so that the return is not sucking when that zone is not on? I have asked him to quote me for this but I think this would be a much better scenario? Mick :)

renegade wrote:

Thanks for that. I have just spoken to the HVAC guy and he said the return can be sent straight back to the main return and not outlet to another room. The only thing is that he has to put in a dampner so that the return is not sucking when that zone is not on? I have asked him to quote me for this but I think this would be a much better scenario?

A much much better scenario........... now you have to ask him where your fresh air is coming from. Rod