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

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.

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Originally Posted by 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?

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The energy model can parse out the annual energy savings associated with a specific improvement. So if it were modelled - you could see if it projected saving $1 worth of electricity or $100. Its my experience that these projections are very helpful. They don't hit the bull between the eyes, but at least they hit the side of the barn.

Flex duct is not considered a durable duct material. Relative to metal duct, life expectancy is about 1/10th. So making an expensive durable permanent improvement to something considered disposable seems absurd.

This is where the bit about perspective comes in. Remember: "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."

For some of this you'll have to recognize when we have a different perspective and attempt to get on board. Or you can resist, but you'll be left standing on the dock.

thanks again for the responses, I think foaming the whole roof deck is beyond her budget.

Radiant barriers are other options (don't waste time on radiant barrier "paint" if a genuine radiant barrier is what you want. It's not a radiant barrier, it's a "low-e" paint, that's all), along with "cool roof" choices when it comes time to reroof the house. We went with a cool roof just recently at our house...the reduction in attic temperatures on hot days is remarkable. More gain than had I got up there and wrapped all the ducts with another layer of insulation.

All of the pro responses you've received have a common thread...consider the return on time and money for effort expended. Wrapping ducts? Maybe not all that expensive but it is very labor intensive, and must be done carefully to avoid creating condensation traps. Foaming the roof deck? Expensive, labor intensive, but it will not only get the ducts into a more temperate environment, it will do the same for the whole attic. "Cool roof" options? Only if you live in a predominately cooling climate. Done right it will be the best thing short of moving the ducts into the house itself, and pertaining to a reduction in cooling costs might outperform a foamed roof deck (see the FSEC study that explains this).

The ultimate solution, not one many can either afford or if they can will go for, is high reflectivity, high emissivity roofing material, followed by insulation at the roof deck, sealing the attic from the exterior, putting ducts in conditioned space.

The stupid thing we keep doing over and over is putting highly solar heat ray absorptive roofing materials onto our houses. We would not even be having discussions like this if logic prevailed over aesthetics (although there is a happy compromise to be had between these two aspects) regarding roof reflectivity.

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Originally Posted by newstudent

thanks again for the responses, I think foaming the whole roof deck is beyond her budget.

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That's the place to start. How much does she want to spend? The number should be monthly so you can do a proper analysis. You need a way to make everything into apples.

Monthly is easiest for people to get their heads around, and the energy savings, which will help carry the cost of the improvements, will be monthly.

So, everything starts with budget. (actually, it starts with bill analysis, but sounds like we are past that)
Next, you model the house
Next, you model the improvements (ie - attic r60 instead of r12)
Next, you price the improvements
Next, you run the energy savings

Now you know cost. Net monthly cost of improvements.

The improvements where the monthly cost is less than the savings, those are the ones you obviously select because they are essentially free. The money currently being spent on energy simply gets reallocated to improving the value, comfort, and energy efficiency home. How much of your home would you prefer to own, and how much of it do you want to rent from the utility company? You are paying for net zero monthly cost improvements whether you own them or not.

Then, pick the "net monthly" cheapest improvements (or improvements that may be desired for non-energy reasons - like windows) until you start getting close to the monthly budget.

In NY, with On Bill Recovery, the capital cost get's rolled into the energy bill, which has guarantees not to change.

Tedd kidd, I understand your approach, but this design problem is in such an obvious need of improvement, it makes my skin crawl just knowing she bought a house with ducts in the attic and pays Bills in excess of $400 some months. When I go into lowes or home depot in the middle of summer and they have their huge 20' garage loading doors open and AC air is just pouring out all day I feel the same way.

"The stupid thing we keep doing over and over is putting highly solar heat ray absorptive roofing materials onto our houses. We would not even be having discussions like this if logic prevailed over aesthetics "

Absolutely! Tried to get a meatl roof on my home and HOA said no, due to aesthetics!

Quote:

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Originally Posted by newstudent

"The stupid thing we keep doing over and over is putting highly solar heat ray absorptive roofing materials onto our houses. We would not even be having discussions like this if logic prevailed over aesthetics "

Absolutely! Tried to get a meatl roof on my home and HOA said no, due to aesthetics!

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Your HOA needs to become educated. Direct them to www.coolroofs.org for starters. HOAs have value on one hand in that their purpose is to uphold property values and neighborhood appeal. But they can also be obstinate about certain things. And I understand some of them are not even operated by the residents who must be subject to the HOA...its administration is farmed out! We need first to stop "farming out" so many things, and be more directly in contact with matters that affect our daily living. Next, entrenched thought patterns need to alter to match the reality of our time. There are cool roof options, even metal ones, that are aesthetically attractive AND deliver reduced attic temperatures. HOAs need to pull their head out of the sand and grapple with this.

Quote:

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Originally Posted by newstudent

Tedd kidd, I understand your approach, but this design problem is in such an obvious need of improvement, it makes my skin crawl just knowing she bought a house with ducts in the attic and pays Bills in excess of $400 some months.

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Yes, but she's in the enviable position of not needing to move quickly. So take advantage of it. Don't do the "poke n hope".

If you rush to treatment, you are likely to miss big opportunities for cures. If you throw a bunch of insulation in that attic and the bills don't abate you might conclude the next step is a blower door test. If that test indicates the house is really leaky, the insulation will need to be removed in order to seal the leaks. How ya feeling now?

Curing a disease is usually a much nicer long term approach than treating it. Right now you are both assuming the problem, and assuming the cure.

The more assumptions you make, the greater the risk of being proven wrong.

Quote:

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When I go into lowes or home depot in the middle of summer and they have their huge 20' garage loading doors open and AC air is just pouring out all day I feel the same way.

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We all feel that one...

Hey! Check this out! OP is going to LOVE this...!

DOE/Steven Winter Assoc has recently completed a study and built standards for spray foam insulating duct in attics. I attended a webinar where the author, Bill Zoeller presented their findings. It was fantastic:

http://bit.ly/sprayfoamducts

Early adopters will need to be significantly involved in the process to insure quality, probably having to lead the contractors until these strategies and best practices for implementation trickle to the field.

Attachment 327661 Attachment 327671 Attachment 327681 Attachment 327691

You can encapsulate unburried duct. It doesn't meet Challenge Home requirements so you wouldn't design this way, but apparently is a significant improvement for retrofit:

Attachment 327701

Here's my spray foam picture album for those interested.

"
Early adopters will need to be significantly involved in the process to insure quality, probably having to lead the contractors until these strategies and best practices for implementation trickle to the field. "

that's for sure. I emaied steve winters and asked him for a contractor to recommend. he forwarded my email to some insulation spray company. they sent my email to someone on this board who emailed me back saying that he didn't think spray foaming ducts was a good idea for my sisters home.

I never told anyone it was for my sister's home except for board members that's how I know what a small world it is.

OP...strange indeed.

Teddkidd..lets talk more about the spray foam ductwork on building science forum.

glad to see you are keeping busy spraying foam...that is what you
are currently doing?

I'm doing a little private consulting.

In March 2011 the program came out with cost effectiveness rules that required projects have a minimum SIR (savings to investment ratio) of 1.01. This was a complete departure from the "every job that saves energy MUST be run through" policy prior.

Our founding mission was to do accurate modeling and thorough comprehensive design. Although not required by the program, we trued our models down to actual consumption. Like dropping the annual mileage you drive a Prius from 50,000 miles to 30,000 miles, truing models to actual drives SIR down.

Our project SIR's were coming in at .5 to .7. So unfortunately the choice we faced was not true models, and game numbers when close to 1.01, or leave.

The problem is, once you track results you understand how all the numbers connect. You understand that, if you are diligent accurate realization CAN occur. The numbers go from foggy hypothetical theory, to reality. The promise can deliver.

So we chose to leave.

as ted says:
If you throw a bunch of insulation in that attic and the bills don't abate you might conclude the next step is a blower door test. If that test indicates the house is really leaky, the insulation will need to be removed in order to seal the leaks

this is often what I encounter. then you have to dig thru the
insulation to get to the leaks, making a not so difficult job really
difficult & time consuming.
otoh..dirty existing insulation is an indication of air leakage.
dig under the discolored insulation..and there is your leak.

pros and cons to both.

I understand your frustration with your sister's situation.
does she have anyone who can help her with some work in
the attic? sealing ducts with mastic & doing some air
sealing work could only help. it isn't rocket science just takes
time & patience.

best of luck.