Calling all HVAC wizards...do I need to run a duct in this room?

jcramsey

Well-Known Member
Joined
Jul 22, 2009
Location
Marion, NC
In the final stages of building an addition on our house. Trying to figure out if I need to run a new HVAC duct to into it or not. ~1500 sq ft house with 220 sq ft addition. 3 ton heat pump. I'm taking out the doors separating the living room and the addition so will be mostly open between them. Two registers dumping right above where each opening will be. Just wondering if that would be sufficient or if I need a dedicated duct for that room too. Probably have just enough room to squeeze a new duct in above the door frame if I need to.

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Just go ahead and do it, no regrets later. Unscientific.
 
You will very much need additional ducts.

And if SC is anything like NC, you will need another return as well. Anything over 1600sq ft is required by code to have at least 2 returns.

And I don’t know that I see a jack stud under the header on that door to the right? Could be the angle of the picture.
 
rockcity said:
You will very much need additional ducts.

And if SC is anything like NC, you will need another return as well. Anything over 1600sq ft is required by code to have at least 2 returns.

And I don’t know that I see a jack stud under the header on that door to the right? Could be the angle of the picture.
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Thanks. I'll give an AC guy a call and see what I need to meet code.

You're correct on no jack stud on that door. The right side has one and the other door has them on both sides. :rolleyes:
 
Fabrik8 said:
Looking at the reflection in the doors, it looks like there are a lot of windows on the addition. I'm no HVAC wizard, but I can spot a lot of solar gain when I see it.....
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There are a lot of windows. Two out of three sides stay pretty well shaded for the better part of the day. There are two windows and a door that get some direct afternoon sunlight though. We keep the blinds shut on that side of the house about 99% of the time.
 
@1500 sq ft of conditioned space already on a 3-ton system you're pushing its limits as it is. Rule of thumb is 1 ton per 500sqft. With 220 square foot added, if you can, run a piece of 8 inch flex duct inside the ceiling and split off into two 6" for the supply. If you can hover the supply lines on the exterior wall right above the windows that would best. You'll definitely want to add another return. 10" or 12" would suffice.
 
If'n it were me, I'd run two new 8" ducts into the addition, put volume dampers on both ducts, add volume dampers to the ducts in the living room, and balance it to push most of the air into the addition. Alternatively, you might could extend the two ducts over the doors into the addition, but you're going to have less control that way.

I'd be less concerned with solar gain than with the generally high u-value of a window, and the ratio of exterior envelope to enclosed space. The insulation in the addition isn't going to be great, especially so with that vaulted ceiling.
 
shawn said:
If'n it were me, I'd run two new 8" ducts into the addition, put volume dampers on both ducts, add volume dampers to the ducts in the living room, and balance it to push most of the air into the addition.
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THIS. I do commercial HVAC for a living. Granted, I do pharma but air is air. :lol:

If this was one of our buildings I'd recommend terminal HEPAs with a single zone supply air valve with reheat and a return air valve.
 
Inspector stopped by this morning and I talked to him for a few minutes. He said if I tapped into the ducts over the doors like @shawn suggested, no permit would be needed, which is appealing. I'm wondering if I using a T and adding dampers to the living room would help control the flow into the addition. I'm sure its not the best solution, and the wisdom is to run the new ducts and a return, but doesn't hurt to talk about the options.

Also, he said I didn't need another return...at least to pass his inspection. Whether I need one for system efficiency is another story.




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jcramsey said:
Inspector stopped by this morning and I talked to him for a few minutes. He said if I tapped into the ducts over the doors like @shawn suggested, no permit would be needed, which is appealing. I'm wondering if I using a T and adding dampers to the living room would help control the flow into the addition. I'm sure its not the best solution, and the wisdom is to run the new ducts and a return, but doesn't hurt to talk about the options.

Also, he said I didn't need another return...at least to pass his inspection. Whether I need one for system efficiency is another story.
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If he doesn't need a return for his inspection then I wouldn't worry about it. Houses are so leaky anyway that it won't affect efficiency really.

The problem I see with tapping into those two grilles is that there is probably very little room in there to do anything. Although maybe it is attic space above it. If you tee off there and use the same duct, you can just damper it off at the grille. You have less control and more noise but you can screw around with it for the seasons too. My old house had a jacked up HVAC system and I had a bathroom and a bedroom that would get all weird conditioned so that in the winter I had to dump all the air into one bedroom and flatten out the bathroom and then in the summer it was the other way around.
 
Just run dual wind-er units in there....plenty of windows to chose from to get optimum performance. Your neighbors won't think any less of you than they already do......:gitrdun:

Also I think there is a piece of Mira-Tec trim used for a jack on that one door...we'll just do the same on the other side since it been holding strong for 15 years ....I mean half that roof was held up by a 2x6 nailed into two pieces of that stuff :rockon:
 
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Blaze said:
If he doesn't need a return for his inspection then I wouldn't worry about it. Houses are so leaky anyway that it won't affect efficiency really.

The problem I see with tapping into those two grilles is that there is probably very little room in there to do anything. Although maybe it is attic space above it. If you tee off there and use the same duct, you can just damper it off at the grille. You have less control and more noise but you can screw around with it for the seasons too. My old house had a jacked up HVAC system and I had a bathroom and a bedroom that would get all weird conditioned so that in the winter I had to dump all the air into one bedroom and flatten out the bathroom and then in the summer it was the other way around.
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It's tight, but it does go into attic space so it could work. Think I will call the AC guy out and see which option is less work for him/cheaper for me.
ramjo said:
Just run dual wind-er units in there....plenty of windows to chose from to get optimum performance. Your neighbors won't think any less of you than they already do......:gitrdun:
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Why stop at just two? :cool:
 
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