If cutting a new hole in the trunk, what do you do about the insulation, just trim it around the hole and leave it be, or do you need to tape the edge somehow so fiberglass fibers don't get into the airstream ?
HVAC duct issues
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EbS-P
Minister of Fire
Sure m, but I’d add at least one somewhere else.
You don’t want exposed fiberglass in the air stream. If you have duct board after thirty years it may be lost cause. All my old take offs in the duct board nothing was taped or really sealed. Happy to get rid of that nasty stuff.
Really? Is that common in your area cause I've never heard of that. We always have the insulation wrap on the outside. How do you keep the insulation from getting blown all over the place? And doesn't the insulation restrict airflow compared to having a smooth duct wall? Wow I have so many questions
EbS-P
Minister of Fire
No replacement unless you want to. It’s a lost cause trying to keep the fiberglass out of the air stream. Cutting one more hole and not taping it won’t make much difference in 4 weeks. The duct board can not be mechanically cleaned. They have encapsulation aerosol products but it’s expensive.
EbS-P
Minister of Fire
Wow, well I guess I'll find out when I cut the hole. Amazing to think it might be bare sheet metal (with no insulation). Especially in the first 25 years I lived here, when the crawlspace was not encapsulated.
Ok, I finally cut into the metal trunk. There is indeed insulation on the inside of it. It's about a 1"-thick layer of a substance resembling fiberglass insulation, with a layer of something resembling tar-paper covering it, attached to the inside of the metal trunk with some kind of fasteners kinda like rivets (except they don't penetrate to the outside of the metal).
When I add two new takeoffs (to re-locate those two flexduct runs that are really long and attached to the narrowed-down part of the trunk, see pix in OP), I'm wondering if I need to do anything to the edges of this insulation layer. The stuff doesn't seem like it'd give off fibrous particles as badly as fiberglass batts would, and I don't really think the air velocity is enough to pick them up anyhow. On one of them, I taped all around the edge with mastic tape, but it was a pain and I'm thinking unnecessary.
EbS-P
Minister of Fire
So it was duct board inside metal….. interesting. I doubt two new holes would shed much fiberglass. Cutting new holes will do more than not taping.
I want to known how that was constructed, in half’s?? Anyway duct board can’t be mechanically cleaned. Not used much anymore in residential.
Duct board ? It wasn't rigid at all.
It looks to me like regular rectangular-cross section metal trunk. Not sure how the insulation got in there.
EbS-P
Minister of Fire
Maybe they did just put the. Tarpaper fiberglass on the inside. That’s what all my metal ducts were wrapped with on the outside. Makes more sense that they could just roll it out and poke through the fasteners.
Fiberglass Duct Liners, Fiberglass Awareness, Page 1
When you line an air duct with the fiberglass insulation on the inside, you cannot properly clean the duct. This page shows examples
fiberglassawareness.com
Oh lord. You nailed it. That's the stuff. I think I have a major problem. My wife sneezes probably at least 30 times a day (not exaggerating). And has had pneumonia several times in the past two years. And she's otherwise a pretty healthy person. Of course, that's clearly a website with an agenda (per its name); I need to look into this more.
I don't know if ripping out the liner is even practical. But I'm able to access a lot of the inside in this process of relocating those two takeoffs and replacing the MBR takeoffs with dampered ones. Not sure I even need insulation on the trunk, it all being in an encapsulated crawlspace - in the summer it's a total non-issue (stays in the 60s there) and even the winter it rarely or ever goes below 60 degrees.
EbS-P
Minister of Fire
We lived in a house 12 years with fiberglass ducts that were not great. I haven’t looked into real research about how dangerous these products are once they are 40+ years old. My gut tells me they rank in the middle bad things in a home.
What I learned getting ours replaced. You need to see every system in a home with a finite useful life. Your fridge 10 years, AC compressor 20, ductwork 30-40, electrical 50-75. Ect.. nothing lasts forever. Truth is yours is at the end of its useful life. Having ducts that don’t leak (and are oversized) have resulted in a more uniform temp in the house and increased comfort. It was time to replace it all. Add extra returns and a whole house dehumidifier. Not once during this summer did I need my second stage of cooling. That’s right a 2000 sq foot house with original insulation and new windows with a 1100 sq ft basement was cooled on 25k btus.
As a second point the new duct insulation (and probably the dehumidifier running keeping the supply ducts warmed) means warmer supply temps at the registers. I had un insulated reruns in the vented crawl space.
Honestly I think the less you disturb it the better if it looks anything like mine most of the fiberglass is covered by a good layer of dirt.
Now there are duct encapsulation products/professionals. It seems like it’s a last resort where you don’t have access to the ductwork
So either leave it alone or rip it all out and replace. Expensive or a big DIY undertaking.
I did find this stuff I could spray on the places where I cut into the duct liner for new takeoffs. Of course, pretty sure the original installers didn't use it. https://www.carlislehvac.com/product.aspx?id=136
I did find this stuff I could spray on the places where I cut into the duct liner for new takeoffs. Of course, pretty sure the original installers didn't use it. https://www.carlislehvac.com/product.aspx?id=136
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Yeah sorry I wasn't trying to scare you or anything, I haven't done any research on this myself and it's my first time hearing of such a thing. I just always assumed insulation got wrapped on the outside of ductwork.
That website obviously thinks it's bad news, and it could be, but I would dig a little deeper before ripping everything out.
That website obviously thinks it's bad news, and it could be, but I would dig a little deeper before ripping everything out.
EbS-P
Minister of Fire
That’s about my take away. I do think if someone has a sensitive respiratory system having ducts you could clean may be important. Products like this and duct board are probably in millions of homes. More important is controlling humidity IMO.
You say the airflow has issues that temps aren’t consistent, you are upsizing a new hvac system. You have fiberglass duct liner. I would be planning a complete duct replacement in 2 years or less.
So finally got a cheap manometer and measured some static pressures. Supply seems decent, 0.25 iwc or so (measured between furnace and indoor coil). But return side (measured just before furnace) is 0.5-0.6 iwc. Way too high.
I reckoned it was the washable filter I've been using. So I bought a quality disposable filter (Filtrete 1085) and tried that. But even with filter grill open (so nothing whatsoever in the return airstream) I was getting 0.5. There is 6-8ft of 16" flex, with a sharp 90-dgeree bend, in the return, I guess that's the culprit. Gonna have to address that with the new system.
I reckoned it was the washable filter I've been using. So I bought a quality disposable filter (Filtrete 1085) and tried that. But even with filter grill open (so nothing whatsoever in the return airstream) I was getting 0.5. There is 6-8ft of 16" flex, with a sharp 90-dgeree bend, in the return, I guess that's the culprit. Gonna have to address that with the new system.
EbS-P
Minister of Fire
Is the total static pressure within spec of your unit. At .85 it’s high but I’m guessing it is within allowed values.
EbS-P
Minister of Fire
The problem is, because of the way the house's original HVAC was installed, the return comes down not far offset from the supply trunk. In the rightmost of the two pix in my OP, you can see the 16" flex from the return coming into the indoor unit, which is perpendicualr to the supply trunk.
Maybe I can take out that kink in the supply trunk, but I think the foundation piers may prevent it. Still, the return airflow doesn't need to be as spastic as it is now. And the new indoor unit should be a little shorter (horizontally) than the current one (which is furnace plus indoor coil), since it'll use heat strip backup, or it'll be a communicating inverter-based type with no backup heat.
Maybe I can take out that kink in the supply trunk, but I think the foundation piers may prevent it. Still, the return airflow doesn't need to be as spastic as it is now. And the new indoor unit should be a little shorter (horizontally) than the current one (which is furnace plus indoor coil), since it'll use heat strip backup, or it'll be a communicating inverter-based type with no backup heat.
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