flex duct hung from attic ceilings vs. laid on attic floors?

[newstudent]

My home has the attic flex duct laying on the floor of the attic in North Carolina,

My sisters home in Orlando, FL has it suspended from the ceiling.
She's thinking of burying the flex duct under the blown fiber glass insulation as this article describes.
http://www.etccreations.com/hvac/atticducts

Which got me wondering why the flex duct is suspended off attic floor to begin with?

[Mr Bill]

My home has the attic flex duct laying on the floor of the attic in North Carolina,

My sisters home in Orlando, FL has it suspended from the ceiling.
She's thinking of burying the flex duct under the blown fiber glass insulation as this article describes.
http://www.etccreations.com/hvac/atticducts

Which got me wondering why the flex duct is suspended off attic floor to begin with?

Has to be hung up in Houston per code. If it's laying on the floor, the bottom side of the flex can begin to condensate because of the dew points, also it most likely to be pulled loose by the cable guy, you know the bull in the china closet guys?

[energy_rater_La]

duct is suspended to allow better air flow. ducts that bend, twist & are crimped
reduce delivered air flow. code is no more than 2" sag in 4' of flex.
not many companies do this..but some do. it isn't rocket science, just time
and effort to do it right.

in humid climates burying ducts in insulation on attic floor creates condensation
around the duct where it touches the insulation..or another duct.
maybe it works in Penn. where article is from, but not in humid climates.

a better investment is mastic seal of ducts and either strapping them
up (no more than 2" sag in 4') or creating an unvented attic with foam
insulation at the roofline.
with either, mastic sealing of ducts is needed.
existing homes have lots of duct loss, between unsealed or badly sealed
ducts, returns, plenum connections and supply boxes 30% duct loss isn't
uncommon.

look for information based on the climate you live in. florida solar energy center
would be a good unbiased site for her to visit.

best of luck.

[beenthere]

He has a little problem with his math on that site also. He doesn't allow for the thickness of the flex insulation, and uses 5.5" of blown insulation in an area that would only be 1.5 to 2"

Then he suggest blowing an extra 3" over top of the duct. but doesn't mention that the extra insulation will crush the flex ducts insulation lowering its R value. plus it can crush or oblong the flex reducing air flow.

[tedkidd]

She's thinking of burying the flex duct under the blown fiber glass insulation as this article describes.
http://www.etccreations.com/hvac/atticducts

Why?

Does she have a problem she's hoping to cure? Or "hey, this seems like a great idea and I've got money to throw at stuff."?

[newstudent]

Why?
Does she have a problem she's hoping to cure? Or "hey, this seems like a great idea and I've got money to throw at stuff."?

Yes her problem is that her electrical bill is high due mostly to AC use and according to the article it helps reduce energy. She's going to get Radiant Barrier installed.

Would buying roll fiberglass insulation withOUT a vapor barrier and wraping it around the hanging flex duct be better? condensation will obviously still have the ability to form between the humid air and foil flexduct skin, but unlikely to do damage since it is off the ceiling floor.

3" of blown fiberglass insulation is very light, I would of never guessed it would crush the flex duct insulation significantly.

I've read FSEC web site and they basically suggest adding a vapor barrier. They make no mentioin of increasing the flex duct R value by increasing the insulation around it.

I realize that Central Florida is more humid than the Carolinas, but we get really humid here too and I have never noticed condensation in/around the attic flex tubes.

[jimj]

Here is a little info for you.
http://www.energyvanguard.com/blog-b...h-in-the-Attic

[jimj]

Also pay special attention to the comments below the article by David Butler and John Tooley.

[tedkidd]

Yes her problem is that her electrical bill is high due mostly to AC use and according to the article it helps reduce energy. She's going to get Radiant Barrier installed.

Would buying roll fiberglass insulation withOUT a vapor barrier and wraping it around the hanging flex duct be better? condensation will obviously still have the ability to form between the humid air and foil flexduct skin, but unlikely to do damage since it is off the ceiling floor.

3" of blown fiberglass insulation is very light, I would of never guessed it would crush the flex duct insulation significantly.

I've read FSEC web site and they basically suggest adding a vapor barrier. They make no mentioin of increasing the flex duct R value by increasing the insulation around it.

I realize that Central Florida is more humid than the Carolinas, but we get really humid here too and I have never noticed condensation in/around the attic flex tubes.

This approach is called "the poke n hope". Typically "let's try this" provides little to no satisfaction, and an empty wallet, are the result. Sales pitches selling products that promise solutions, without accountability for results are a sucker trap. Don't fall for them. Solutions come for comprehensive understanding and customized design, not from magic products.

She needs to take a comprehensive look at where her homes energy is going. Develop an informed and thoughtful plan of attack. Throwing money at crappy ideas expecting to get anything other than crappy results is delusionally optimistic.

See the bottom line of my signature. You need to understand the illness before prescribing cures. Not the what, but all the Y's.

[jtrammel]

This approach is called "the poke n hope". Typically "let's try this" provides little to no satisfaction, and an empty wallet, are the result. Sales pitches selling products that promise solutions, without accountability for results are a sucker trap. Don't fall for them. Solutions come for comprehensive understanding and customized design, not from magic products.

She needs to take a comprehensive look at where her homes energy is going. Develop an informed and thoughtful plan of attack. Throwing money at crappy ideas expecting to get anything other than crappy results is delusionally optimistic.

See the bottom line of my signature. You need to understand the illness before prescribing cures. Not the what, but all the Y's.

X2

[newstudent]

" Sales pitches selling products that promise solutions, without accountability for results are a sucker trap. Don't fall for them."

Where did this come from?!? Sorry there aren't any insulation salesmen knocking down our door. Insulation is a proven product, not snake oil.

Obviously increasing the insulation around ducts will cause less energy loss. Ducts used to be OK at R6, now R8 is the code in many places, for obvious reasons.

All I"m asking is the best way to do it.
#1. With vapor barrier ( on or off attic floor)
#2 Without vapor barrier. ( on or off attic floor)

I've personally tried #1 in the carolinas and never noticed any moisture issues. When I stick my hand underneath the added blanket of insulation the ducts feel very cool. They never felt that way before. Obviously it is lowering energy transfer and causing the AC to run less. How long will the return on investment be? I have no idea, but it was cheap to get installed.

[hvacvegas]

[I][B]
All I"m asking is the best way to do it.
#1. With vapor barrier ( on or off attic floor)
#2 Without vapor barrier. ( on or off attic floor)

#3 No insulation.

"in humid climates burying ducts in insulation on attic floor creates condensation
around the duct where it touches the insulation..or another duct.
maybe it works in Penn. where article is from, but not in humid climates."

"Then he suggest blowing an extra 3" over top of the duct. but doesn't mention that the extra insulation will crush the flex ducts insulation lowering its R value. plus it can crush or oblong the flex reducing air flow. "

"She needs to take a comprehensive look at where her homes energy is going. Develop an informed and thoughtful plan of attack. Throwing money at crappy ideas expecting to get anything other than crappy results is delusionally optimistic"

and I x4.

On or off, whatever. Refer to local codes. To many variables depending on location specifics, especially the size/shape/build of the attic.

[energy_rater_La]

ok ok...lets slow this roll.

personally I've wondered about wrapping unfaced batt insulation around existing ductwork.
even the lowliest R-value (R-13) is twice what code here in La. mandates. (we are still
at R-6..not R-8 whiny builders association members connected to good old boy politicians.)

just never had a house I could do that kind of experiment on. I've seen old hard duct with
R-2 kraft paper ductwrap..circa 1930's installed..get this..tied with string around the ductwork.
why wouldn't it work with existing vapor barrier & R-whatever unfaced batts?
I can't think of why it wouldn't. would I do it? not until I had a chance to verify it
for myself. without the vapor barrier on added insultion..would condensation occur
at 1st vapor barrier?? I don't know..don't think so..but can't test my theory on
my clients. in my house..ducts are inside living space, so can't diy here..but I do
wonder..

so for your sister's house..do read the energy vanguard article & comments. they
cover all the points about condensation & ducts.

my climate is hot humid..maybe not as humid as your sisters..but it sure seems like
@ 95%RH it should be raining..but it isn't always the case.
burying the ducts just doesn't work for us. I've seen houses where you could
trace the path of the ductwork inside the house by the water stains on
the ceilings.

the best option..although not a quick solution, is to seal house leakage.
then seal duct leakage, strap ducts, rb or foam or conventional insulation.

blower door testing measures amount of air leakage into the house,
and used properly can show you exactly where leakage occurs.
duct testing, like blower door testing measures total amount
of duct leakage...and also can show you where it leaks.

once leakage sites are sealed, using proper materials that last
& don't shrink or dry out..then suspending ducts to get them off attic
floor & insulation should be done.

the reason people don't think that the ducts condensate when they rest
on the insulation is because they check them at the wrong times of the
day. even when ducts are attached too close together on the plenum
they condensate. if the insulation jackets touch..they condensate.
add in leakage at duct take off..and plenums can be very wet depending
upon time of day. some stay wet all the time..every house varies to some degree.

adding a radiant barrier helps to reflect heat out of the attic, but ducts are
still exposed to attic temps.
completely sealing attic with foam insulation creates an unvented semi conditioned
attic. temps outside and inside attic will be close. not 5 degrees warmer than the house..
semi conditioned. this helps out in that ducts are in cooler attic.
as air barrier & thermal barrier (foam insulation) is now at the roofline
rather than the attic floor..all the little leaks from inside the house
into the attic don't suck as much as they do normally.

the trade off is this..seal leakage at attic floor/ceiling
recessed cans, oversized cuts at supply boxes, bath fans
just to mention a few..or foam insulate.
first is labor intensive with inexpensive materials
the second is just expensive. done in one or two days
for average sized house.
still before foam..bath fans have to be vented out
of attic, insulation has to be moved from eaves of house
so that foam can make a complete roof to attic floor seal.
so foam requires prep work also.
in either case duct/return leakage should be sealed.

usually these decisions are budget dependent. so having
an energy rating helps to weigh the upgrades/costs &
homeowners budget against costs & performance of upgrades.

this is a good time of year to do attic work. not as extreme outside
& in attics. for hvac & insulation companies we are getting into a slower
than heat of summer/cold of winter time of year.

research what you can..ask lots of questions & consiter an unbiased
testing, improvement & verification rating/audit.
hire an independent, or take utility free audits & know that you
can save more than 10-15% of your utility costs.
the things you learn from the testing will suprise you.

best of luck.

[Shophound]

The problem with wrapping any duct in an attic that already has a vapor resistant jacket (vinyl or foil) with unfaced insulation is that the unfaced section is vapor permeable. It is possible...how likely depends on several factors...that the formerly exposed jacket, now covered by permeable insulation, will cool to the dew point of the attic air temperature when the a/c is running.

In the 1930's, very few ducts in houses carried cooled air...only heated.

[thermojohn]

It is possible...how likely depends on several factors...that the formerly exposed jacket, now covered by permeable insulation, will cool to the dew point of the attic air temperature when the a/c is running.

Agreed. In the humid south, it is a common occurance every night for ducts in ventilated attics to reach dewpoint. Anything touching flex duct will cause it to sweat. Any sweat not evaporated (due to permeable insulation wrap) by the hot attic temps the next day remains to continue to condense the next night, leading to more saturated insulation.

It is a very common thing for folks to turn their t-stats down at night to 68 degrees for sleeping which creates more opportunity for ducts to reach dew point.

[tedkidd]

" new student" implies an openness to learning. Hmmm. Genuine?

In any event, +3:

It is possible......that

jacket, now covered by permeable insulation, will cool to the dew point of the attic air temperature when the a/c is running.

Resulting in a soggy, moldy, rotting mess in the attic.

Run off half cocked and you may get lucky, or you may end up dealing with a litany of unintended consequences us "old students" warned you were lurking.

There is a process. Taking shortcuts generally means missed opportunities and sometimes means expensive consequences.

[newstudent]

" new student" implies an openness to learning. Hmmm. Genuine?
Resulting in a soggy, moldy, rotting mess in the attic.
Run off half cocked and you may get lucky, or you may end up dealing with a litany of unintended consequences us "old students" warned you were lurking. There is a process. Taking shortcuts generally means missed opportunities and sometimes means expensive consequences.

So basically what you are saying is that if I get condensation I should NOT wrap the ducts with insulation, but if I DON"T get condensation it is OK.

So If I just spend $20 and get some insulation and wrap a seciton of the pipe and see what happens?

Seems like no one really knows if it will make condensation.
Obvioulsy water stain marks on the ceiling are an issue, but would wrapped insulation really get that soggy. I just can't imagine it staying soggy for long when the temperature up there is 120F or more.
Her duct work is already sealed with mastic.

Her budget doesn't allow for spray foaming the entire roofline.

I've been researching this and radiant barrier and sealing up duct work are the top recommendations.
Is there a product where you can remove the exsisting duct work vapro barrier and increase the insulation with a new vapor barrier, that would obviously work well.

[tedkidd]

Yeah, you want simple answers so you can take action. Unfortunately, the action you want to take has a lot of risk. Getting the details wrong may mean disappointing results, or worse.

The first step is have a comprehensive home assessment. You are jumping from "high energy bills" to "cure specification" without the comprehensive diagnostics or cost benefit analysis step. Hyper simplification leads to disappointment.

There are a huge number of dependencies. We can't see your house, and you don't have the necessary knowledge or tools to map them. Your focus on products rather than solutions is hard to break. Unfortunately, if you don't have the ability to step further away this will not make sense to you.

You could take building science classes. But you'd still be short experience and $10,000 worth of tools.

[energy_rater_La]

really ted? this is how you explain things & continue a discussion?

I shouldn't have wondered aloud (aka in my earlier post) about wrapping ducts
in unfaced batts. that was my mistake. sorry for sidetracking your post OP.

OP,the problem with removing existing insulation vb jacket, and wrapping ducts with extra insulation
and vb is labor & performance.

there is no product to do this.

with flex duct, removing the (vb) insulation jacket & wrapping existing insulation with
another layer of insulation is at best difficult.
then to seal the new vapor barrier would create another
set of problems as to what materials to use...
both for the vb and to make vb continous and sealed.
certain tapes seal certain products. others fail quickly in extreme
attic temps.
you can imagine that over the years tradespeople and homeowners have tried
different methods. none work well enough to be approved by acca.

if ducts are suspended then air circulates around them and dries the condensation.
ducts do condnesate in hot humid climates. there is no question of that.
whether the homeowner feels/sees this
or not is dependent upon what time dewpoint was reached, and what time homeowner
makes the inspection.
I usually find wet ducts early in the morning. however if ducts touch each other
or lie on insulation on attic floor..then the condensation doesn't always dry.
this is because the air does not circulate around the vapor barrier of the duct.
wet insulation decreases the r-value of the insulation to 0. if the insulation
doesn't dry, each time dewpoint is reached it gets wetter.

if the air doesn't circulate the condensation doesn't dry. doesn't matter how hot the
attic gets.

correctly installed flex duct..straight tight runs with gentle curves rather than
sharp drops and bends.
ducts suspended with duct strap..not tight to the roofline, but suspended again,
in straight runs with gentle curves & no restrictions..its an art in itself.

as long as I've been doing this, I still have to
step back and re-adjust the straps to keep ducts straight. now I know folks
who don't..they get it right first time..but they've been at it longer than my 10+ years.

personally I think sealing ducts, running & strapping ducts is as important as
equipment install. but that isn't common thinking for most hvac companies.
the person who does ducts is generally the low pay person on the job.

I don't think anyone is saying if the ducts get condensation don't wrap but if the don't
condnesate do wrap..that is climate specific information. as you can see from the link
you posted in penn..it is ok to bury ducts in the insulation.
but not in hot humid climates.

the internet is great for info..but you have to consiter where it comes from. location wise
and who is providing the info.

radiant barriers do provide some help for ducts in attic.
I have a rb, so does shophound. we have different types, but both of us
have found benefit of this install.

I do understand the cost of foam puts it out of range for a lot of people.
so in this case, sealing the air barrier between the attic and the living space
below, attic floor and ceiling of living space, is a good first step.
once the air barrier is tight then you have less communication between the
conditioned and unconditioned spaces.

then mastic sealing ducts, supply boxes, plenums, plenums to equipment & r/a
is step two.
third step would be strapping ducts off insulation.

adding rb if that is her choice, and more insulation on attic floor.


best of luck.

[newstudent]

"Unfortunately, the action you want to take has a lot of risk. "

No it doesn't, worst case scenario, humidity is trapped and I'll blow $20 on insulation during a test.

According to this article
http://www.foxbusiness.com/personal-...ts-worth-cost/
for just a little bit more than the cost of the energy audit I could hire someone to insulate the duct work.

Below are some links to sample home energy audits. Why is it that none of them recommend increasing the insulation around duct work? When government studies and independent ones cite having duct work in attics is a 15% energy waster?
http://www.nrel.gov/docs/fy10osti/48163.pdf


http://www.carolinahomeenergy.com/re...uditReport.pdf
http://www.scotthomeinspection.com/d...dit-Sample.pdf
http://www.oxbowinspections.com/energyauditsample.pdf
http://www.greenchipstocks.com/repor...ergy-audit/369
http://deckerhomeservices.com/Sample...gy%20Audit.pdf