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Old 05-03-2007, 07:53 PM   #1
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Do I need a HVAC return vent in basement?


I'm finishing an unfinished basement room in a two-year-old home. Half of basement room (one full wall about 11 ft. high x 22 ft long) is below grade, and then the rest of thick, poured concrete walls step down, following the slope of the earth outside (home is built into a steep slope). I've added three AC ducts to this room (to the HVAC which sits in this room and will be partioned into a "closet"), two vents in the room and one vent in the full bath that I'm putting in the room. Room, being that half of it is below grade, had very mild temps before renovation. That has caused some to say that I don't need an AC return vent in the room. I think I do need it, for air filtration, and to help filter out any extra humidity. I'm already planning a dehumidifier in a closet that will also house the basement bath's sump pump, but I think I'd still like to have the AC return vent. Before renovation, basement HVAC primarily serviced main floor above basment. Before I started renovation, one HVAC tech said my HVAC could handle me tapping into system to cool the new basement room but I didn't ask about the need for the return. What do you think? Thanks!

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Old 05-04-2007, 01:32 PM   #2
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Do I need a HVAC return vent in basement?


I would think that to pass code, you would need one

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Old 05-04-2007, 01:44 PM   #3
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Do I need a HVAC return vent in basement?


we only need one big return air vent in the open area of our basement... somewhat down on the wall... that was in the approved plan submitted to the city...
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Old 05-07-2007, 07:26 AM   #4
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Do I need a HVAC return vent in basement?


Place a low return in main area, this will pull cold air off the floor making it more comfy in the winter and remove damp air in the summer.The important thing to remember is not to over size these areas if mechanical room is near by.(cumbustion/make up air)
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Old 05-07-2007, 08:43 AM   #5
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Do I need a HVAC return vent in basement?


Quote:
Originally Posted by coolmen View Post
Place a low return in main area, this will pull cold air off the floor making it more comfy in the winter and remove damp air in the summer.The important thing to remember is not to over size these areas if mechanical room is near by.(cumbustion/make up air)

Very good observation, that no one else has made......you want to stay well away from your laundry room and HWT (hot water tank), so as not to draw combustion air away from these items. (or cause a negitave draft).

Last edited by harleyrider; 05-07-2007 at 08:46 AM.
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Old 05-10-2007, 10:10 AM   #6
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Do I need a HVAC return vent in basement?


Hmm...this negative draft issue (great info, by the way, thanks)...my basement room to be finished is roughly, before framing, 16 x 22, and the HVAC and Water heater are in the corner of this room and will be partioned off into their own 8 x 4 closet (A/C is electric, Heater is gas, and water heater is gas). But, there are two 6" to 8" vents (one about a foot off the ground and another about 8' up) between the HVAC and water heater that run to the outside that the builder installed when they stubbed my basement room. I did want to run the return to one end wall of this closet that I am describing (vent intake obviously sitting on the livable room side of this closet). Won't these two vents to the outside that the builder installed be sufficient for my HVAC and water heater to get the air they need. Also, since we're on the subject, another question I had, could having these two vents to the outside possibly mean that I don't have to use an ugly louvered door on this HVAC and water heater closet?

And finally, just to be sure, a couple of people thought I didn't even need the return since the basement is typically mild (half of the basement room is underground)? Does anyone buy this? Thanks!
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Old 05-10-2007, 01:27 PM   #7
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Do I need a HVAC return vent in basement?


In my opinion, if you have open louvers for combustion air, high and low, to the outdoors, you are truly lucky and actually had a quality home builder!

Assuming these louvers are sized correctly for the appliances within (which they likely are, unless you have upgraded), you are correct, you would not need a louvered door to your space (I'm assuming that your AC return air is entirely ducted and there is no return grille/opening right at the unit).

If indeed you can get all your combustion air through those vents, not only could you use a solid door (beneficial for noise reduction and looks), but you should even look into an insulated door (as well as insulating the closet walls) so that the outside air coming in those louvers doesn't waste energy from the home conditioning.

As for the low return question, although common wisdom states that a low return forces the warm heating air down to the floor (since it would otherwise rise and stay at the ceiling), actual flow studies (such as the demonstration at the Titus air diffuser factory in Dallas) have shown that this is mostly a myth. The way to get warm air down to the floor is to size the supply diffuser correctly such that the "throw" (distance that the air flows from the face, based on leaving velocity) forces the air to reach the floor. Obviously, if you have ceiling grilles for cooling, the cold air will "fall" to the floor. But for heating, you have to get enough airflow that the diffuser "blows" it to the floor (or else oversupply to the point where the whole room just gets plenty warm enough). Yes, you will get a warm floor area right in front of a low return grille, as all the warm air finds it's way there, but the thought that the whole floor will be warmed because of a low return is actually mostly a myth.

I would try to get a return grille somewhere in the room - or else make sure that there is an open return air path (a door that is louvered, or never closed, to the upstairs). But if you can't get the return grille at the floor without great difficulty, I would say that any grille is better than no grille at all - as long as you properly size the supply diffusers (and that may simply be a matter of properly adjusting the integral dampers according to whether you are in heating or cooling mode).
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Old 05-10-2007, 01:48 PM   #8
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Do I need a HVAC return vent in basement?


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In my opinion, if you have open louvers for combustion air, high and low, to the outdoors, you are truly lucky and actually had a quality home builder!
I suppose it is ok in Florida... but in area with snow and minus degree.... that will lost heat?
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Old 05-11-2007, 11:23 AM   #9
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Do I need a HVAC return vent in basement?


Thank you for the long, thoughtful reply, pjpjpjpj! You went over my head with some of the diffuser and integral damper lingo , but, still, this is great info that I know I can put to good use! Unfortunately I have more bad things to say about my builder than good (just found out they didn't put Tyvek or some type of house wrap on my new home over the OSB, they may have made it just before the code change, and of course I can't make them come back and put it on now, and that's actually another diychat question I have: how bad will things get for my home without the wrap?); anyway, I suspect that because they stubbed my unfinished basement, the two vents to the outside must've been code, but from what you said I am happy to have them however they got there. I'm going to try to get the return installed and I'll let you know how I do. ...as to the next reply about having the open louvers to the outdoors in a cold climate, I'm in the Southeast so the snow and minus degrees aren't an issue for me, although, as pj suggested, I do want to think about keeping that room shut, so long as I can be sure that my vents to the outside are big enough. Thanks again!
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Old 05-16-2007, 06:07 PM   #10
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Do I need a HVAC return vent in basement?


Okay (if anyone's still there), I can do a low return, and now I'm trying to figure out what size my return duct and diffuser / damper should be. Based on the space I have to run the duct above the HVAC unit, I'm thinking the return duct should be 8" (I know the duct flexes but I still think 10" might be too big). But, is there some formula that tells you what size / diameter the return grill and ducts should be? The basement room was 352 sq. ft. before I framed it so it's a little smaller now, and the ceiling is 8 ft. tall. I have three vents feeding the room (I don't recall the size of those ducts at the moment, please let me know if you need those vent sizes to figure the return). Thanks!
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Old 05-17-2007, 08:55 AM   #11
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Do I need a HVAC return vent in basement?


One way to do this is by the convenience of your framing... pick the locatiion of the vent and see how large it fit there most easy to install... a bit bigger won't harm...
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Old 01-28-2009, 10:47 AM   #12
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Do I need a HVAC return vent in basement?


I am a builder myself and as for tyvek being a code in my area is not the case.Tyvek rumors of code below brick, has and as of now, is still a myth.
Below siding and brick should be an approved moisture resistant material.
Osb and stryofoam panels both suffice with no other covering.
Some practices are considered good practices but never actually hit the state code book such as tyvek,but i also dont know in your state if that the case.
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Old 01-28-2009, 01:09 PM   #13
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Do I need a HVAC return vent in basement?


Don't install a dehumidifier in the same closet as your bathrooms sump pump. You could end up pulling fumes from it.

Don't go overboard on supplies and returns for this room.

It won't need much air for heating or cooling.
Install teh return that it sized large enough to return the same amount of air as the supplies, but not more.

You don't want to put this room into a negative pressure when the system runs.

Since its doubtfull your supplies will shoot air down to the floor. A low return will work better.

What size is your furnace.
With teh combustion air intake you have, it may be enough for bothe the water heater and furnace. And if so, then you don't want a louvered door to teh furnace room.
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Old 04-03-2014, 02:43 AM   #14
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Do I need a HVAC return vent in basement?


Definitely you need return ducts for room, you must contact your HVAC contactor to design the duct work properly.

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