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Discussion Starter #1
Just curious if anyone knows anything about this field which is driving me to drink.

Thanks,
John
 

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Why do I have ridiculously cold air coming out of my registers when the system is off? I can get more specific if it helps. :)

Let me ask an even better question... where could I go to get duct insulation that has an R-value 6 or higher? (HD, Lowe's, etc. don't have much of a selection.)

Ohh yeah I should have clarified residential HVAC (as opposed to the system in a car).

Thanks,
John
 

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where does your furnace pull the air from outside or does it pull air from around it ?
 

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Discussion Starter #6
rednsilver94sc said:
where does your furnace pull the air from outside or does it pull air from around it ?
It gets it from a couple of returns in the ceiling.

All the ducting is in the attic; after the system is off, apparently the ducting gets really cold and then the air (upper 30s in some spots) drops into my home. Seems to be a major source of heat loss. I'm wondering if adding some extra insulation to the ducts would really help the situation or if I'd be more like peeing in the ocean, so to speak.

J
 

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I work in the HVAC industry. I would insulate all the ductwork that runs through an unconditioned space. That will reduce the heat loss and natural convection from them chilling.

You can use conventional pink batting or some of the foil backed stuff to wrap the ducts. Find some foil tape to seal all the joints between ductwork sections before you wrap everything in insulation, use more foil tape to seal your insulation to itself. With your area use as high an 'R' factor as you can reasonably work with, something like R-12.
 

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How is the insualtion in the attic?

Also, some AHU's have a fresh air duct....if it does, for the winter time, you might want to shut it off.
 

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Discussion Starter #9
Thanks guys for all the input -- it's appreciated.

Here's a pic that shows my situation. This is at the end of the supply line where it's by far the coldest when the system is off. I think there's a natural air flow in the home that causes the air to move from the beginning of the supply line to the end, forcing air out of these supplies. I think this air flow is caused by normal temperature differences in the home.



The metal trunk plenum is insulated on the inside, but I suspect the R-value is quite low since it's only like half an inch thick, but it's that very dense insulation. Here's a pic of the inside:



The flex ducts are also insulated and some (the originals) are rated R-5.79 (kind of a weird number) but I'm not sure what the new ones are rated, probably 4.2 since they're Goodman and Goodman is a POS. Home Depot has some R6 insulation that's intended for ducting. It's the fiberglass with the silver lining type. I was thinking of maybe slipping that over the existing flex duct. Maybe I'll use the pink stuff for the actual metal duct since there aren't a lot of duct-specific offerings at the box stores.

I just don't want to spend a lot of money and do it wrong, y'know? 'Cause there's a lot of real-estate to cover.

And this is just so y'alls don't think I'm smokin' crack:



To quote Chris Tucker, "Thirty-Eight degrees?! Who you think you kidnapped, Chelsea Clinton?!" Okay he didn't quite say that but you get the point.

Thanks again,
John
 

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Ok situation confirmed. I would add some batting to the metal duct. As far as I understand the insulation inside is mainly to damp sound. I don't know what to tell you to do about the flex duct they are tough to work with.

Depending on how your returns are run (my 'rents house has them in the interior wall cavities) you could improve your efficiency in the winter by moving the return air openings to the wall right next to the floor and get some covers/dampers for the summer time to have it pull from the ceiling still. This would also help with the cold air 'falling' on you from above and reduce the gravity circulation of the air.

Oh yea, your attic space looks like its gonna suck to work in, sorry.
 

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JMags said:
Ok situation confirmed. I would add some batting to the metal duct. As far as I understand the insulation inside is mainly to damp sound. I don't know what to tell you to do about the flex duct they are tough to work with.
I will do that -- thanks for the info. It just occurred to me however... During the summer time we get really high dewpoints around these parts. By adding insulation to the metal ducting (making it cooler), do I run the risk of creating condensation between the duct and the insulation? That could get nasty. Do I have to put down a vapor barrier or something first? Or maybe I can just get away with sealing the insulation very well with tape?

Depending on how your returns are run (my 'rents house has them in the interior wall cavities) you could improve your efficiency in the winter by moving the return air openings to the wall right next to the floor and get some covers/dampers for the summer time to have it pull from the ceiling still. This would also help with the cold air 'falling' on you from above and reduce the gravity circulation of the air.
Yeah, one of my returns is in the ceiling of my loft (20ft ceiling w/ open layout). Guess where all the hot air goes? Wheeeeee! I'm probably not skilled enough to add in new returns without messing something up. Plus I'm in a condo, second story, not a lot of wiggle room. Suprisingly, when the system is running the temperatures are quite well distributed in the home. Overall I think it's a good design, just needs some kinks worked out.

Oh yea, your attic space looks like its gonna suck to work in, sorry.
LOL... yah. Actually, of the three primary areas, that one is the easiest to work in. And yes, I have punched a hole in a ceiling in the past. I just want this done and over with. I never want to go up there again.

Many thanks again,
John
 
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