Re: Re: Air Conditioning Duct Work

[Guest guest]

Semco,Metal duct wrapped in either fiberglass or aluminized bubblewrap should be just fine. The fiberglass is nasty to work with, and difficult to fit so that it expands to it's full thickness. Where it's compressed (which is almost always will be, in many parts of the system) it never reaches it's theoretical R-value. Bubble wrap has a much lower *theoretical* R-value, but it goes on quickly and certainly, and is much easier to seal with certainty. Metal duct is much more durable than flexduct, especially at the connections. And smooth metal has much less air flow resistance than flex duct. Flex duct simply does not last all that long. It leaks and comes apart, in my experienceBut here's the really important point: make sure that *all* the joints are sealed with mastic (the goopy stuff) rather than with duct tape. Beyond the duct connections, this caution also applies to smooth metal elbows, which typically have "gores" (the rotating crimped seams which let the elbow bend in the many odd ways required in residential duct work). Also, make certain that the duct connections to the AC unit and/or furnace are gooped up really well. That's where the pressure difference is greatest, so that's where the leakage per inch of seam is also the greatest.Field measurements by the Florida Solar Energy Center, the Lawrence Berkeley Lab and the New York State Energy Research & Development Authority consistently show that nationwide, the losses from air leaks from duct connections account for upwards of 25% of the building's annual HVAC energy (the sum of the heating, cooling and fan energy, not the "plug loads" controlled by the occupant's electrical appliances).So the nature of the insulation is really quite trivial compared to the air-tight integrity of the ducts. And it really makes no sense to install a "high efficiency" furnace or AC unit is the duct joint leaks are going to add 25% to the annual HVAC energy consumption.I suspect that, if your contractor favors metal duct, he or she already knows this and will take care to seal those connections. But it's worth confirming that sealing with mastic is in his plan, prior to applying the insulation. Applying mastic is cheap, and it's far more effective than worrying about the insulation thickness or it's type.Tight duct connections will give you a more comfortable home, and one which uses much less energy to achieve that result.Lew--------------------------------------------Lew HarrimanMason-Grant ConsultingP.O. Box 6547Portsmouth, NH 03802(603) 431-0635LewHarriman@...On Dec 26, 2008, at 6:48 PM, semco_semco_semco wrote:Chuck,Thank you. Everything you said makes sense. I would agree immediately to medal ductwork that was wrapped in fiberglass insulation, just not the bubble wrap. The other concern I would have with metal would be 90 degree turns, which is not good.Fortunately, all the duct work will be run in the attic which will be conditioned.I will check further on the metal duct work using the fiberglass insulation on the outside of the ducts.Thanks again.>> Semco, etc.> > IMHO, metal (usually galvanized) ductwork is superior to flex. The flex wll > cause greater disturbance of airflow within, thus reducing the efficiency of > the system, and (something I recently learned myself (credit Tony Havics)) > the coils used to keep the flex duct expanded actually create small eddies > and dead spots in the airflow within the duct (part of the disturbance) > resulting in greater accumulation of dirt within the duct.> > Flex duct can't be cleaned as easily or effectively as metal either due to > the irregular interior surface, and the more fragile material. Therefore, I > usually recommend replacement of the flex when it gets dirty. Not a big > deal in easily accessible areas and short runs, so much depends upon your > configuration. As I'm somewhat familiar with your situation and what you're > striving to accomplish, I don't recommend using the flex.> > My familiarity with insulated metal duct is that it is usually insulated on > the interior with fiberglass (NOT a good idea) or that the exterior is > fiberglass wrapped. I'm not familiar with bubble wrap used as insulation, > however it may pose some concers with the plastic offgassing.> > Otherwise, and theoretically, all insulation accomplishes it's purpose by > creating dead air space. The concept of bubble wrap therefore makes sense > from that perspective, as the bubbles, and once wrapped with foil, the > entire bubblewrap structure becomes a series of symmetrical and contiguous > dead air spaces. Not a bad idea, but I'd want more information including > the type of plastic used & it's potential for offgassing, as well as R value > ratings of the bubble wrap as compared to more traditional fiberglass outer > wrapping. Fiberglass of course brings along it's own set of potential > problems and concerns.> > I disagree that if the bubble wrap is properly engineered it's going to > facilitate conditions favorable to microbial amplification. Like > fiberglass, the plastic is non-organic and therefore does not supply a > nutrient source. If there are no voids in the installation, or subsequent > damage to the integrity of the bubble wrap insulation, there should be no > condensation problems, as should be the case with any duct insulation. So > again, it goes back to proper engineering, competent installation, and due > care to ensure it is not damaged. I'd also want to know what the plastic > material's expected useful lifespan is, and how it may be affected over time > by heat and ozone exposure, which may cause more rapid deterioration.> > Bottom line is that if it were my house, I'd probably want metal duct with > the exterior wrapped with fiberglass insulation, at least for the main > lines, and particulary within wall cavities, etc., exept perhaps the > inclusing of some short, accessible runs of flex duct to cut down somewhat > on costs.> > Chuck Reaney> > Alpha Environmental, Inc.> IAQ/IEQ & Environmental Consulting> Media, PA 19063> > P: F: C: > > Air Conditioning Duct Work> > > Hello everyone. Again, can you PLEASE help me.> > I had an air conditioning contractor try to convince me that I should use > metal duct work> through out my house. The way he described it the metal had no insulation, > but was> wrapped with "bubble wrap", then wrapped with foil. Yes, the same bubble > wrap used in> packing.> > My common sense is that this is only an invitation for moisture from the > cold metal and I> cannot imagine Bubble wrap being insulation for anything. Seems like it > would be an> invitation for MOLD.> > Other contractors are proposing using flex duct, which I understand has > fiberglass insulation> then coated with plastic in the center which will make a clean air > compartment.> > Any thoughts, or remarks? All would be appreciated.>

[Guest guest]

Dear Semco:

Another goal when designing the duct layout is make it as streamlined as

possible. The goal here is to minimize the energy needed to move the intended

amount of air. Options include having as few bends as possible, using two 45s

instead of one 90, or using a larger radius 90 where it can't be avoided.

Imagine that the air molecules are tiny tennis balls and that making them change

directions wastes energy.

Just a thought.

--

LIFE ENERGY ASSOCIATES

20 Darton Street

Concord, MA 01742-5710

www.LifeEnergyAssoc.com

--------- Air Conditioning Duct Work> > > Hello everyone. Again, can you PLEASE help me.> > I had an air conditioning contractor try to convince me that I should use > metal duct work> through out my house. The way he described it the metal had no insulation, > but was> wrapped with "bubble wrap", then wrapped with foil. Yes, the same bubble > wrap used in> packing.> > My common sense is that this is only an invitation for moisture from the > cold metal and I> cannot imagine Bubble wrap being insulation for anything. Seems like it > would be an> invitation for MOLD.> > Other contractors are proposing using flex duct, which I understand has > fiberglass insulation> then coated with plastic in the center which will make a clean air > compartment.> > Any thoughts, or remarks? All would be appreciated.>

[Guest guest]

Semco,

You're welcome. Don't worry too much about 90 degree turns in the metal

duct. A proper installation will include turning vanes...pieces of sheet

metal (vanes) within the duct at 90 degree turns that serve to more smoothly

direct the airflow around the turn.

As we've discussed before, just make sure that EVERYONE involved in the job

knows what they're doing & does it well, and don't assume anything.

Best Regards,

Chuck

Air Conditioning Duct Work

>

>

> Hello everyone. Again, can you PLEASE help me.

>

> I had an air conditioning contractor try to convince me that I should use

> metal duct work

> through out my house. The way he described it the metal had no

> insulation,

> but was

> wrapped with " bubble wrap " , then wrapped with foil. Yes, the same bubble

> wrap used in

> packing.

>

> My common sense is that this is only an invitation for moisture from the

> cold metal and I

> cannot imagine Bubble wrap being insulation for anything. Seems like it

> would be an

> invitation for MOLD.

>

> Other contractors are proposing using flex duct, which I understand has

> fiberglass insulation

> then coated with plastic in the center which will make a clean air

> compartment.

>

> Any thoughts, or remarks? All would be appreciated.

>

[Guest guest]

Lew:

All very good comments/suggestions. Great stuff! However, one item omitted by the responses to Semco’s question.....Sheet metal duct is better (no doubt), but round (versus square or rectangular) sheet metal ducting is best. While square (or rectangular) ducting is cheaper and at times easier to install, round is best for mitigating pressure losses and minimizing settled dirt. Not to mention, round ducting cleans really well while the bottom corners of square ducting cannot be effectively cleaned.

For what it is worth....

Semco,

Metal duct wrapped in either fiberglass or aluminized bubblewrap should be just fine. The fiberglass is nasty to work with, and difficult to fit so that it expands to it's full thickness. Where it's compressed (which is almost always will be, in many parts of the system) it never reaches it's theoretical R-value. Bubble wrap has a much lower *theoretical* R-value, but it goes on quickly and certainly, and is much easier to seal with certainty. Metal duct is much more durable than flexduct, especially at the connections. And smooth metal has much less air flow resistance than flex duct. Flex duct simply does not last all that long. It leaks and comes apart, in my experience

But here's the really important point: make sure that *all* the joints are sealed with mastic (the goopy stuff) rather than with duct tape.

Beyond the duct connections, this caution also applies to smooth metal elbows, which typically have " gores " (the rotating crimped seams which let the elbow bend in the many odd ways required in residential duct work). Also, make certain that the duct connections to the AC unit and/or furnace are gooped up really well. That's where the pressure difference is greatest, so that's where the leakage per inch of seam is also the greatest.

Field measurements by the Florida Solar Energy Center, the Lawrence Berkeley Lab and the New York State Energy Research & Development Authority consistently show that nationwide, the losses from air leaks from duct connections account for upwards of 25% of the building's annual HVAC energy (the sum of the heating, cooling and fan energy, not the " plug loads " controlled by the occupant's electrical appliances).

So the nature of the insulation is really quite trivial compared to the air-tight integrity of the ducts. And it really makes no sense to install a " high efficiency " furnace or AC unit is the duct joint leaks are going to add 25% to the annual HVAC energy consumption.

I suspect that, if your contractor favors metal duct, he or she already knows this and will take care to seal those connections. But it's worth confirming that sealing with mastic is in his plan, prior to applying the insulation. Applying mastic is cheap, and it's far more effective than worrying about the insulation thickness or it's type.

Tight duct connections will give you a more comfortable home, and one which uses much less energy to achieve that result.

Lew

--------------------------------------------

Lew Harriman

Mason-Grant Consulting

P.O. Box 6547

Portsmouth, NH 03802

LewHarriman@...

[Guest guest]

What type of filters do you recommend. I was planning on using Electric, not

electrostatic, but Electric filters. They are the best I can find to filter out

the smallest things.

The kitchen, are you referring to the exhaust? Or the junk that gets into the

filters from regular cooking when not using the exhaust?

>

> Subject: Re: Air Conditioning Duct Work

> To: iequality

> Date: Friday, December 26, 2008, 5:14 PM

> Flexible duct has a high static pressure drop due to the

> ripple/concertina internal surfaces and therefore while you

> can use

> it for short runs, the agregate lenth of flexible duct

> should not

> exceed 6metres/20feet.

> This is why all long runs NEED to be mostly done in smooth

> solid

> duct.

> I also don't like the idea of the plasticised liners on

> a lot of

> ducts as the static generated by dust particles passing

> over the

> liner tends to conglomerate the dust into the valleys of

> the duct.

> Remember that the filters that you are probably using only

> entrain

> about 30% of the finer particles, that residue that still

> passes

> through your system either deposits within the system on

> the coils or

> the duct, or isw delivered into your conditioned space.

> The bubblewrap insulation may possibly be more of an

> example that the

> HVAC guy uses in his explanations than what is the reality.

> Anything

> with an R value better than 1.5 is probably ok for inside

> areas - but

> if the ductwork is exposed to outside air temperatures and

> humidity,

> you may wish to elevate this.

> We recommend that any flex duct on kitchen exhaust be

> replaced at not

> greater than 5-yearly intervals and the owners when they

> see the 5-

> year duct come out - usually want to replace with solid

> cleanable

> duct. So please don't think of flexible duct as being a

> healthy

> alternative.

>

>

> >

> > Hello everyone. Again, can you PLEASE help me.

> >

> > I had an air conditioning contractor try to convince

> me that I

> should use metal duct work

> > through out my house. The way he described it the

> metal had no

> insulation, but was

> > wrapped with " bubble wrap " , then wrapped

> with foil. Yes, the same

> bubble wrap used in

> > packing.

> >

> > My common sense is that this is only an invitation for

> moisture

> from the cold metal and I

> > cannot imagine Bubble wrap being insulation for

> anything. Seems

> like it would be an

> > invitation for MOLD.

> >

> > Other contractors are proposing using flex duct, which

> I understand

> has fiberglass insulation

> > then coated with plastic in the center which will make

> a clean air

> compartment.

> >

> > Any thoughts, or remarks? All would be appreciated.

> >

[Guest guest]

Semco,

I'm not crazy about electrostatic or electric air filters. Honeywell makes

a filter/housing known as a " media filter " . Trane, I think has also

developed a similar system that is supposed to be rated higher than

Honeywell's. Call me old-fashioned, but I still don't think anything beats

a deep pleated filter with a traditional medium. The Honeywell is available

in two different MERV ratings, and is what I have installed in my home,

along with a 1 " pleated prefilter. Yes, that arrangement does create a

pressure drop that isn't ideal, but since we smoke and have two dogs and a

cat, plus use a wood stove for most of our heat, it's a trade-off I'm

personally willing to live with.

The Trane wasn't available when I had the Honeywell installed, so it's

possible that I'd have gone with that if it had been based upon the claims

of superior performance.

If you need more specific info, let me know and I'll look it up for you if

you can't find it.

Chuck Reaney

Alpha Environmental, Inc.

IAQ/IEQ & Environmental Consulting

Media, PA 19063

P: F: C:

Re: Air Conditioning Duct Work

>> To: iequality

>> Date: Friday, December 26, 2008, 5:14 PM

>> Flexible duct has a high static pressure drop due to the

>> ripple/concertina internal surfaces and therefore while you

>> can use

>> it for short runs, the agregate lenth of flexible duct

>> should not

>> exceed 6metres/20feet.

>> This is why all long runs NEED to be mostly done in smooth

>> solid

>> duct.

>> I also don't like the idea of the plasticised liners on

>> a lot of

>> ducts as the static generated by dust particles passing

>> over the

>> liner tends to conglomerate the dust into the valleys of

>> the duct.

>> Remember that the filters that you are probably using only

>> entrain

>> about 30% of the finer particles, that residue that still

>> passes

>> through your system either deposits within the system on

>> the coils or

>> the duct, or isw delivered into your conditioned space.

>> The bubblewrap insulation may possibly be more of an

>> example that the

>> HVAC guy uses in his explanations than what is the reality.

>> Anything

>> with an R value better than 1.5 is probably ok for inside

>> areas - but

>> if the ductwork is exposed to outside air temperatures and

>> humidity,

>> you may wish to elevate this.

>> We recommend that any flex duct on kitchen exhaust be

>> replaced at not

>> greater than 5-yearly intervals and the owners when they

>> see the 5-

>> year duct come out - usually want to replace with solid

>> cleanable

>> duct. So please don't think of flexible duct as being a

>> healthy

>> alternative.

>>

>>

>> >

>> > Hello everyone. Again, can you PLEASE help me.

>> >

>> > I had an air conditioning contractor try to convince

>> me that I

>> should use metal duct work

>> > through out my house. The way he described it the

>> metal had no

>> insulation, but was

>> > wrapped with " bubble wrap " , then wrapped

>> with foil. Yes, the same

>> bubble wrap used in

>> > packing.

>> >

>> > My common sense is that this is only an invitation for

>> moisture

>> from the cold metal and I

>> > cannot imagine Bubble wrap being insulation for

>> anything. Seems

>> like it would be an

>> > invitation for MOLD.

>> >

>> > Other contractors are proposing using flex duct, which

>> I understand

>> has fiberglass insulation

>> > then coated with plastic in the center which will make

>> a clean air

>> compartment.

>> >

>> > Any thoughts, or remarks? All would be appreciated.

>> >

>

>

>

>