HVAC Ducting

Charles Gifford

Greetings,

Located in the NE Florida area. This is a rather long winded description followed by a short question.

Ran across a single family two story home yesterday where the HAVC contractor ran the ducting (felx duct) to the second floor (second floor is bonus room, closet and bathroom) by compressing the ducting between the rafters of the second floor roof.

There is no allowance for air space to circulate around these ducts nor is there space in the bays between the rafters for insulation where ducting is installed. The ducting will be compresed when sheetrock is installed.

We are required in our area to have the rafters firred out to ensure that the insulation does not get compressed and that there is adeauate air space for vetilation. Additionally, it is my understanding that the flex duct manufactures do not want the ducts compressed, and want air to be able to circulate around the ducting.

My concern with this installation is condensation either inside the duct or outside the duct in this rafter bay. Is this a legitimate concern?

Than you in advance for your comments.

Charles

Earthfire

duct space

Flex duct does not retain volumne like metal round duct when squeezed, it looses area to flow air . But I wouldn't worry too much about that particular house cause it will probably burn in not too long a time from the stretched and kinked at staples wires. Low bid strikes again

don_9

Its a shame

Why would any body run flex in a area where you can not make a repair in the future.Should be hard duct.But why take that route when you have a knee wall right there?
Most are confuse with duct location.High are low?Which ever path you take its either going to suffer in winter or will
suffer in the summer (Its force air)Sure you should be concern with all the roofing nails poking in the flex, dew point=condensate.As stated above its that low bid thing.
Try not to be to hard on the hvac guy,he just caught up with
that builder mentality,hopefully he will learn soon.

John T_2

What more do you want?

> Greetings,

>

> Located in the NE Florida area.

> This is a rather long winded description followed

> by a short question.

>

> Ran across a single

> family two story home yesterday where the HAVC

> contractor ran the ducting (felx duct) to the

> second floor (second floor is bonus room, closet

> and bathroom) by compressing the ducting between

> the rafters of the second floor roof.

>

> There

> is no allowance for air space to circulate around

> these ducts nor is there space in the bays

> between the rafters for insulation where ducting

> is installed. The ducting will be compresed when

> sheetrock is installed.

>

> We are required in

> our area to have the rafters firred out to ensure

> that the insulation does not get compressed and

> that there is adeauate air space for vetilation.

> Additionally, it is my understanding that the

> flex duct manufactures do not want the ducts

> compressed, and want air to be able to circulate

> around the ducting.

>

> My concern with this

> installation is condensation either inside the

> duct or outside the duct in this rafter bay. Is

> this a legitimate concern?

>

> Than you in

> advance for your comments.

>

> Charles

John T_2

What more do you want?

Each room needs a supply and in some cases a return opening. This contractor, like so many others, seems to have done his part. You can't really expect the most efficient design can you? After all the customer probably didn't want to pay for a "good" job anyway. Hell, the homeowner will never know somethings wrong until he's long gone.

All kidding aside, I wouldn't worry about condensation, condensation would most likely occur on the exterior of the duct if the surface was cool enough to reach dew point. More than likely the near zero R-value the duct will have once compressed will eliminete any cooling effect. Heat gain thru conduction could even heat the second floor during the summer. Probably on a black roof to boot.

As contractor I believe the consumer is due a proper job no matter what price I've agreed to do the job for. If I can't make any money on an accepted contract then shame on me. I should have walked away from the job.

John

Unknown

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Floyd

Don't worry about it....

if he run flex duct that far you won't get any air out of it anyway!!!!!!
Rip it out and go with nothing and you will be better off all the way around.
Flex duct, with it's rough insides and low volume is very tough to push air though...
add some bends, squash it, and try to make it go 40 or 50 feet and GEEE!!!!!
I wonder why no air comes out the other end??????

Sorry to be so sarcastic..... just been called to fix these things too many times!!!!!

Do it once, do it right!!!
Sacrifice some closet space and get a decent sized duct up to the second floor!!!!!

Mike T., Swampeast MO

\"Bonus Room\"

Maybe not just the contractor. If not a speculative home at least...

Did HO say "Why don't you just run a couple ducts up there. I'll keep 'em closed until I decide to finish the rooms. It won't cost me much, right?"

Even if you furred out the rafters there'd still be that big kink where it passes between the top plate and the roof sheathing.

If both of those are supplies (BR & Bath) and it's the only conditioned portion of the upstairs, they can forget cooling without a return.