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

[energy_rater_La]

you won't hire someone to unwrap & insulate and rewrap duct system for price quoted in foxbusiness link.
maybe one or two ducts.

in some climates burying ducts is recommended.
ducts in attic waste more than 15%, but architects, hvac & homeowners
still do it.

believe me..if there was a product that provided R-20 ductwork..
hvac supply would stock it, and some hvac companies would install it.
some homeowners would pay extra cost to have it.
sadly..it just doesn't exist.

think of how big & thick the insulation would be on the ductwork. R-19
is 6"..in attics where space is premium & compressing the insulation
derates it..how is it going to work??

[thermojohn]

I have always wondered... We focus on R-50 or more for attic insulation, yet duct insulation is R-4 to R-6. The TD in ductwork is even greater when compared to the TD of the living space.

[newstudent]

After reading the following links the only plausable solution to the humidty issue was to add insulation and then wrap in a new vapor barrier like astro foil.

http://hvac-talk.com/vbb/showthread....ensation/page2
http://hvac-talk.com/vbb/showthread....and-Insulation
http://hvac-talk.com/vbb/showthread....-vapor-barrier

Thanks for those that responded. I've been educated.

"R-19 is 6"..in attics where space is premium & compressing the insulation derates it..how is it going to work?? "

I don't really follow your logic at all. Most attics I've been in our cramped, but adding 6" of extra insulation (12" total, ) is pretty easy , and space is hardly at a premium when the area is never used.

[jtrammel]

You have to break the other vapor barrier before making another

[newstudent]

just slit it several times with a box cutter, pretty easy to do.

[jtrammel]

Yea, just making sure you were aware of that.

[energy_rater_La]

lots of attics and even new construction space is a premium.
one 10" duct with 6" of insulation won't fit in a lot of spaces.

having an attic with lots of space is an exception..most are
tight cramped spaces.

I think everyone agrees that having more insulation on ducts in attics
and crawlspaces is a good idea. that we put ducts & equipment in those
spaces is just crazy.
unfortunately the hvac industry has not found a way to increase R-value that works
in multiple applications.

it takes a lot to bring about industry changes.
good examples are the 2005 move from 10 seer a/c to 13 seer a/c as minimum
efficiency. another is pending May 2013 elimination of 80% gas furnaces
in northern climates.
efficiency is improved in both examples, but it took a long time
for the industry to mandate these changes.
ductwork efficiency has gone from R-2 to R-4 to R-6 & now R-8 in most areas.

in my area installers complain about the difficulty of attaching R-8
ducts to plenum & supply boxes. to be able to attach 6" of insulation to
start collars & supply boxes would require modification of these pieces.

is this for your house..or your sister's house in florida?

best of luck.

[newstudent]

I'm not sure why an energy audit is being suggested, when this is an obvious problem that energy audits don't even address because putting the duct work in attics is the construction standard.

Here is another good thread about this issue.

http://hvac-talk.com/vbb/showthread....ic-Ducts/page3

it suggests buying the next biggest size flex duct and putting it over exsisting duct work. Basically a tube inside a tube.

And this is the BEST information I have found so far
Study done in Jacksonville, FL
Using spray foam AND burying the ducts! Guess it is possible after all in this humid weather.

http://apps1.eere.energy.gov/buildin...t_retrofit.pdf

[toocoolforschool]

Just put a ductless split system in your attic and call it a day.

[newstudent]

sorry dont' have an extra $10,000 lying around. and you know as well as me that putting a condensor unit in the attic is insane.

[tedkidd]

I used to see things exactly as you see them, and it was really hard to make the shift. It's like learning a new language, then all but forgetting your old one. Communicating that perspective shift is incredibly difficult.

Imagine you have a leaky boat. The boat is sinking. What do you do, plug the leaks? Replace the bilge pump?

What if you replace the pump and the boat still sinks, Failure right?
What if you plug the holes and the boat still sinks, Failure right?

How about gaining understanding of the leakage rate and the pump performance? Incremental improvements tend to have diminishing returns. In our world plugging all the holes is not economically viable, and getting a new pump might be poor investment. If we really want to optimize our efforts we will come up with a plan that optimizes the resources we plan to allocate.

If it takes $1 to plug half the holes, $10 to plug 3/4 of the holes, and $1000 to plug 95%, what investment do you make in plugging holes? You really can't know without understanding the pump, and opportunities for improving the pump. These things are intimately connected.

If it takes $1000 pump improvement to make no hole plugging work, $100 to make $1 hole plugging work, $10 to make 3/4 hole job work, and $1 to make the 95% hole plugging job work.

In this case you can achieve success for $1000, $101, or $20. But the first step is diagnostics, the second is design, and the third is cost/benefit analysis because without them, you don't get these numbers upon which to make an educated decision.

That's what a comprehensive home assessment should provide. It should help you understand and quantify current deficiencies understand where incremental investment should be reallocated.

[newstudent]

OK hypothetically I hire you to do a home energy effciency audit, pay a few hundred and.........

would you ever recommend spray foaming attic flex duct as a solution?

I'm asking because after days of research I've yet to talk to any energy effcincy pro, or read a report that addresses the obvious problem of having duct work in attic in humid climents. (except for the one previously linked to)

Everyone knows it is an issue, it has been brought up multiple times on this forum.

[tedkidd]

Spray foam is difficult enough to apply to flat clean surfaces. But you can ask your consultant what improvements they can, cannot, and prefer to model.

If you paid to mobilize a spray foam rig I don't think you'd want them attempting to coat flex duct. It's a bit like gold plating a turd. Really tough, and in the end what have you done?

I've sprayed rigid, but that is a double benefit of insulating and air sealing, and the guys were there for the rim anyway. I don't see it paying for mobilization.

If you insulate your attic you will want to know leakage before and have some type of leakage after target. Air sealing tends to be the big, often missed opportunity most people miss. Having measurements is you only ability to have a true Quality Control measure.

[jtrammel]

I would recommend spray foaming the roof and sealing the duct if found after testing it would benefit you to do so, this option would be included in the most expensive solution to the houses' problem and it take a special customer to pull the trigger on such an expensive investment but you don't know if they are the one if you don't ask.

[newstudent]

"I don't think you'd want them attempting to coat flex duct. ....... Really tough, and in the end what have you done?"

Is that a rhetorical question? You've increased the R value with a closed cell foam that will not sweat because the dew point temperature will not be reached even in humid areas. Just like the study conducted in Jacksonville, FL pointed out that I linked to.

I've seem some pretty small spray foam rigs, not sure why mobilization is an issue. they can easily fit in the back of a pick up truck and a couple of guys could put them in an attic.

any ways I appreciate your emphasis on air sealing. Deffinetely need to check on that too.

[newstudent]

duplicate post

[tedkidd]

Not well explained.

Spray foam is tough to apply. To a round irregular plastic coated surface, getting a uniform cocoon of foam would be nearly impossible, and I wonder if anyone would attempt it. Flex duct is not considered a very durable material. So improving it on this level might be like replacing the engine in a Yugo. Maybe someone more knowledgable about flex will comment.

It is very likely redefining the attic wouldn't be much more expensive, and that would be much more effective. Might be interesting to see insulating flex modeled. if you get an audit, put that on your questions list.

And if you get a spray foam guy to consider spraying flex please share what they say.

[hvacvegas]

Not well explained.

Spray foam is tough to apply. To a round irregular plastic coated surface, getting a uniform cocoon of foam would be nearly impossible, and I wonder if anyone would attempt it. Flex duct is not considered a very durable material. So improving it on this level might be like replacing the engine in a Yugo. Maybe someone more knowledgable about flex will comment.

It is very likely redefining the attic wouldn't be much more expensive, and that would be much more effective. Might be interesting to see insulating flex modeled. if you get an audit, put that on your questions list.

And if you get a spray foam guy to consider spraying flex please share what they say.

Spray foam on flex is like putting a diamond ring on an old bar whore.

If your going to spray foam anyways, spray the attic.

If you want to get better r-value out of the flex, install foil-faced r-8 flex.

If your want to be green, call a professional.

[newstudent]

" Might be interesting to see insulating flex modeled."


What does that mean exactly?

"Spray foam on flex is like putting a diamond ring on an old bar whore.:"

Why do you say this? Scientific study didn't have anything negative to say about the process. Yes you are a putting a relative expensive type of insulation on a relatively cheaper one, but added together they increase the R value? Right?

[Shophound]

Let's see...spend money to spray foam onto flex ducts, or spend money to spray foam onto the roof deck. Hmm...which to do, which to do??

If those were my only two options, in a heartbeat I would foam the roof deck and leave the flex alone.

Why?

The foamed deck will return more benefit than the foamed ducts. Again, why? The foamed deck is a continuous benefit, whereas the foamed ducts only benefit when the HVAC is running. And does nothing to reduce heat gain or loss to the house at large. Foaming the deck reduces heat gain/loss to the house AND the ducts.