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Old 05-23-2010, 07:27 AM   #1
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Figuring HVAC Needs in Basement


Hey everyone - I'm finishing my basement downstairs, and now getting to the HVAC stage. The unit in the house can handle all the additional needs of the basement (was specifically ordered that way when we built it back in 2007). There were 2 runs coming off the main trunk line to the outer walls when it was just concrete walls. Now I've sectioned off areas into rooms and have more needs. It's probably important to note I've got 9' ceilings and it is fully below grade.
  • I will have a 13x10 bedroom with a 4'x4' window. This room currently has no HVAC run
  • There is a larger entertainment area that is approximately 23'x21'. This area has 1 run going to the middle of the East wall.
  • The bathroom has 1 current run. I intend the keep it there, and not add anything else.
So here are my questions/comments.
  1. I plan on adding a run from the main trunk line to the bedroom on the far west wall. I'm guessing that will be enough for heat (since it's a basement I'm not so worried about cooling). My question in this room is, should I put a return in the ceiling or top of the wall on the opposite side of the room, or will one larger return outside the room suffice?
  2. I will be adding one more run in the large entertainment room to the West wall. Will that with the run already near the East wall be enough to heat that area in the winter?
  3. Finally, I will have a fully leuvered 36" door into the utility room where the unit resides. Is that enough for airflow, or should I place some return vents in these rooms. (I will have an exhaust fan venting to the outside of the house in the bathroom ceiling.)
I've included several drawings. They are pretty much to scale. Included drawings of design and wiring just in case. Any additional thoughts are appreciated.

Thanks,
Chris
Attached Files
File Type: pdf Basement_All Drawings_5-23-10.pdf (54.2 KB, 159 views)

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Old 05-23-2010, 02:54 PM   #2
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Figuring HVAC Needs in Basement


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Originally Posted by cdhen14 View Post
Now I've sectioned off areas into rooms and have more needs. It's probably important to note I've got 9' ceilings and it is fully below grade.
  • I will have a 13x10 bedroom with a 4'x4' window. This room currently has no HVAC run

Thanks,
Chris
Fully below grade, and 4'X4' window, are a contradiction.

So last fall and this spring. When it was 50 to 65 outside. Was your basement as warm as your first floor?

Usually not, since the first floor gets solar gain. But the basement doesn't.
To use your furnace to have your basement at comfort temps. Generally requires zoning.

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Old 05-23-2010, 03:47 PM   #3
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Figuring HVAC Needs in Basement


You would think so. I didn't think it was possible either. When I had the basement built, I had it built with a bedroom in mind. In order to classify it as a bedroom, one of the requirement is to have an escape route other than the door. Since a typical bedroom window isn't considered large enough for that, they dug deeper and wider for the opening. The cement opening in the room is 48" x 48" (off by 1/2" on the height, but whose counting). The window well is further out from the window and had a ladder built into the inside of the well. So yes, it is actually a 4' x 4' window, and it is fully below grade.
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Old 05-23-2010, 04:57 PM   #4
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Figuring HVAC Needs in Basement


LOL... Ok.
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Old 05-24-2010, 05:50 AM   #5
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Figuring HVAC Needs in Basement


Thx for the tip.
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Old 06-01-2010, 05:35 AM   #6
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Figuring HVAC Needs in Basement


So I've decided to move forward with the additional run in the main room (approx. 23' x 21'), which will give that area 2 heating/cooling runs to each side of the room. The bathroom (approx. 9' x 8') will have 1 run, and the bedroom (approx. 9' x 13') will have 1 run. Total of 4 heating/cooling runs in the basement.

Now I just need to focus on return air. The room that contains the Hot Water Heater, Furnace, Water Softner, etc. is appox. 11.5' x 10'. There are no heating/cooling runs to this room. The door that I plan to install here is a 36" fully louvered door. I am assuming that this will circulate enough air from the main area. I think I will also install a return register in the wall of the bedroom near the floor. This should send return air through the bedroom wall, into the hallway, and through the fully louvered door about 3.5' away. I do not plan on putting any return air duct in the bedroom closet. The bathroom will have a ventilation system routed to the outside of the house.

Can anyone verify that this return air plan sounds okay? Any suggestions on how I can improve it. Drawings for the basement are posted in a PDF file near the top of this post.
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Old 06-01-2010, 05:49 AM   #7
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Figuring HVAC Needs in Basement


Are you planning on putting a return in the furnace room?
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Old 06-03-2010, 05:27 AM   #8
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Figuring HVAC Needs in Basement


If I need one, I certainly will. Should I just tap into the existing return air duct on the furnace and put a return cover on it?
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Old 06-03-2010, 05:37 AM   #9
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A return in the furnace room is not allowed. Could draw CO from the furnace or water heater.

If the furnace and or water heater get their combustion air from the rest of the basement area. You need to make sure the return can't draw more air then is being supplied to that area. or it will put it into a negative pressure, and draw CO from the water heater and or furnace.
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Old 06-03-2010, 06:00 AM   #10
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Thanks. I thought I read that about the negative pressure, and didn't think I need one there. What is the best way to determine if the return can/can't draw more air then is being supplied to that area?
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Old 06-03-2010, 06:05 AM   #11
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Will there be any time that the supplies could be closed?

Is the bedrooms door undercut.

A 6" supply to the bedroom won't move as much air, as a 6" round hole or 6X10 return grille in/on the return trunk can draw in. So the return grilles must be smaller then the supplies. How much varies with the position and how clear the return path is to the return grilles.
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Old 06-03-2010, 06:18 AM   #12
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Figuring HVAC Needs in Basement


I suppose there could be times when the supplies are closed. Since I plan to use the space often though, I doubt I would ever shut all of them off. At most I can see myself closing the damper about half way at times.

I have not actually purchased the bedroom doors, but could easily undercut them if that would help airflow in the bedroom.

That makes good sense on the size of the forced air vents and the returns. I am running flexible HVAC tubing from the main forced air trunk into the bedroom. I haven't purchased the boot yet to attached the grill too (nor have I purchased the grill). So I can buy a little bigger of a boot, and be sure I don't buy a large return grill.
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Old 06-03-2010, 06:26 AM   #13
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Figuring HVAC Needs in Basement


Also might want to put an under cut on the door to the basement. So that when you have some of the supplies down there restricted. It can still draw air from the first floor. Instead of the basement.

The draft in a chimney is often less then -.1", it doesn't take long to make a basement match or drop lower then that, when the return is able to draw more air then the supplies put out. So an under cut on the basement door, often can help.

As with any basement. Should also install CO detectors. Co kills weather they are awake or aspleep. But when they are awake. they will often get a headache or show symptoms similar to the flue. Aspleep. No symptoms will be noticed. Until its Too late.

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