Re: Air Conditioning Duct Work

[Guest guest]

Dear Semco:

One advantage that metal duct has over flex duct is that it interior is smooth

sided, and so offers less resistance to air flow and consumes less energy for

moving air through it. Many installations place a limit on the length of

flex-duct that is allowed, probably due to this energy penalty.

--

LIFE ENERGY ASSOCIATES

20 Darton Street

Concord, MA 01742-5710

www.LifeEnergyAssoc.com

-------------- Original message ----------------------

> 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, 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]

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]

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]

I would go with the sheet metal ductwork, also. Make sure it is properly sealed

and

insulated on the outside. Another potential benefit, is that the zinc in the

galvanized

metal is a natural anti-microbial, until the surface gets coated with dust,

anyway. If the

attic space is conditioned, some duct leakage may not be a critical issue.

>

> 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.

>