# HVAC Help needed



## devildog1679 (Aug 3, 2012)

I need some advice on the HVAC set-up for my basement HT (30x11x8.5). The room has foundation walls on 3 sides and on average is at 68° in summer and 66° in winter. Below is a link to a YouTube video that might help illustrate what I’m about to ask.

I believe I have three options. The first is to build dead vents both return/send that draws air from adjacent basement room, seconds is to tap into existing HVAC system, third is a combination of the two. Mini-split is not an option due to cost. Regardless of the option I go with they all have the same basic construction within the HT. The rear of the room will be empty except for a poker table. I would like to build a soffit that runs the length of the 11’ wall and place both the flex tubes for the send/return in that soffit and fill with insulation then DD it. Vents will be on opposite ends. In this area it will be out of the way from the rest of the room. Any pros or cons to this? Also once the flex tubing enters the adjoining room which is a unfinished storage area can the tube and fan just be kept exposed? Is building a soffit with insulation around it needed if sound in this room is not a concern?

Now for the options:

1. Dead vents to draw the air from adjacent room- The flex tube here would be about 15’ long and I was thinking of adding the fan 3’ from the adjacent rooms flex tube end. This way the fan is as far as it can be from the vent in the HT. Is this sound construction? Do I need a fan on both the return/send or just the send?

2. Attaching to existing HVAC- Here the construction in the HT would be the same as option 1. Difference is that when the flex tube enters the adjacent room one vent will be tied into main trunk for send and the other to the return trunk. Here I may snake the flex tube a little bit since the main trunks are close to the HT wall where the tubes exit, about 5’. So I’ll probably add 10’ and just snake around and then circle back to main trunks. Is this sound construction? Anything I can do here to minimize noise transmition to the rest of house through HVAC?

3. Combination of the two- Here I would set it up the same as option 1, where it differs is that I would add a Y to the send flex tube in the adjacent room b/w the fan and HT. I would then add another flex tube to that Y and attach the other end to the main trunk. I would then add a damper b/w the Y and main trunk. I can close the damper in winter when the HVAC is supplying heat, but still get cooler air from the adjacent room by turning fan on. In the summer, I can open the damper to get the cooler air conditioned air and turn off the fan. I could also open the damper to varying degrees to fine tune the theater temperature. Now with this approach not sure if I should do the same to the return and tie it to the main return trunk with a Y as well? 

Any other ideas?


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## bobs77vet (Sep 21, 2012)

Dead vents. i have never heard of this terminology before and i cant see the "you tube" but if this is just an open vent/ductworkwith a fan in it that is suppose to equalize the air from one room to the other i can say i am not a fan of it ( no pun intended). you would be much better off actually connecting everything to the HVAC system. ideally you would want the supply line on the outside of the walls by a window and the return across the room on an inside wall. sometimes you only run the supply lines to the rooms and let a common return line be in an open area, this works if there are wide open spaces. if you are going to use a projector they can put off heat but the size of your room and the temps you are talking about that doesnt seem to be an issue. the more snakes and 90* you use the less air flow you will get....straight runs are your best air flow soloution. my advice is to do this right the first time so the area is comfortable for the long haul.

having each supply line come off of the main trunk as opposed to being spliced in to an upstairs duct run will minimize noise transmission


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## devildog1679 (Aug 3, 2012)

bobs77vet said:


> Dead vents. i have never heard of this terminology before and i cant see the "you tube" but if this is just an open vent/ductworkwith a fan in it that is suppose to equalize the air from one room to the other i can say i am not a fan of it ( no pun intended). you would be much better off actually connecting everything to the HVAC system. ideally you would want the supply line on the outside of the walls by a window and the return across the room on an inside wall. sometimes you only run the supply lines to the rooms and let a common return line be in an open area, this works if there are wide open spaces. if you are going to use a projector they can put off heat but the size of your room and the temps you are talking about that doesnt seem to be an issue. the more snakes and 90* you use the less air flow you will get....straight runs are your best air flow soloution. my advice is to do this right the first time so the area is comfortable for the long haul.
> 
> having each supply line come off of the main trunk as opposed to being spliced in to an upstairs duct run will minimize noise transmission


Just fixed the link and attached is a link to the description of a dead vent. They are very common in HT's.

http://www.soundproofingcompany.com/soundproofing101/the-dead-vent/


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## bobs77vet (Sep 21, 2012)

ok i looked at the you tube video and here are my thoughts, the return and supply need to be seperated more then on just either side of the poker table area. they should be opposite sides of the room length wise. i still dont like the idea of dead vents and i dont think you will be happy with them they may move air but its not the same as being hooked up to the actual trunk lines. as for moving those two trunk lines can they be moved to the other side of the stairs or is there a structural beam running down the middle of the house? you can always move them to the outside wall so the soffit is not in the middle of the room.

i have a new home and the HVAC system has a circulation mode that is always moving the air and it changes the volume of air movement based on some algorithim (sp?). i guess if i didnt have this i could see where people could use the dead vent for air movement in a smaller room but it would still not be the same for heating and cooling purposes but i can see where it would be good for circulating air. maybe in addition to a real supply line yuo could use the dead vent for removing air


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