New HVAC question - duct heat/colling loss in attic
 

I have a question about proper running ductwork in attic.

I have had someone tell me best to have ductwork in an attic next to and
even run between ceiling joist when possible and have the installation blown
in on top instead of having the ductwork hanging from several feet above the
joists. Said that even with insulation wrapped around the ductwork, the
heat/cold in the attic will eventually seep into the duct and will get a
blast of unheated/hot air out when first comes on. By having the duct as
close to the living space when possible and insulating as much on top of the
ductwork keeps the heat/cold loss to a minimum.

I can see where this may make sense, But is this done in any real
installations or would be praticle. I have seen somewhat both ways of being
done, not so sure if that was intended when I have seen the ductwork laying
between or across ceiling joists instead of being hung a few feet above ?

Any ideas as to do/not do it that way ?

Thanks,
MC

"MC" wrote in message
t...
I have a question about proper running ductwork in attic.

I have had someone tell me best to have ductwork in an attic next to and
even run between ceiling joist when possible and have the installation
blown
in on top instead of having the ductwork hanging from several feet above
the
joists. Said that even with insulation wrapped around the ductwork, the
heat/cold in the attic will eventually seep into the duct and will get a
blast of unheated/hot air out when first comes on. By having the duct as
close to the living space when possible and insulating as much on top of
the
ductwork keeps the heat/cold loss to a minimum.

I can see where this may make sense, But is this done in any real
installations or would be praticle. I have seen somewhat both ways of
being
done, not so sure if that was intended when I have seen the ductwork
laying
between or across ceiling joists instead of being hung a few feet above ?

Any ideas as to do/not do it that way ?

I'm not saying it's not done, but i have never seen duct "hanging" in an
attic. Unless you were going to gain a little space, I don't see why anyone
would go to the trouble......

MC wrote:
I have a question about proper running ductwork in attic.

I have had someone tell me best to have ductwork in an attic next to
and even run between ceiling joist when possible and have the
installation blown in on top instead of having the ductwork hanging
from several feet above the joists. Said that even with insulation
wrapped around the ductwork, the heat/cold in the attic will
eventually seep into the duct and will get a blast of unheated/hot
air out when first comes on. By having the duct as close to the
living space when possible and insulating as much on top of the
ductwork keeps the heat/cold loss to a minimum.

I can see where this may make sense, But is this done in any real
installations or would be praticle. I have seen somewhat both ways of
being done, not so sure if that was intended when I have seen the
ductwork laying between or across ceiling joists instead of being
hung a few feet above ?

Any ideas as to do/not do it that way ?

Thanks,
MC

I have a couple of ducts in my attic and they sure are not hanging.

--
Joseph Meehan

Dia duit

My ductwork pretty much is on hangers in the attic but my builder was a
moron.


"Dr. Hardcrab" wrote in message
news:AiAde.8589$nN.1953@trnddc05...

"MC" wrote in message
t...
I have a question about proper running ductwork in attic.

I have had someone tell me best to have ductwork in an attic next to and
even run between ceiling joist when possible and have the installation
blown
in on top instead of having the ductwork hanging from several feet above
the
joists. Said that even with insulation wrapped around the ductwork, the
heat/cold in the attic will eventually seep into the duct and will get a
blast of unheated/hot air out when first comes on. By having the duct as
close to the living space when possible and insulating as much on top of
the
ductwork keeps the heat/cold loss to a minimum.

I can see where this may make sense, But is this done in any real
installations or would be praticle. I have seen somewhat both ways of
being
done, not so sure if that was intended when I have seen the ductwork
laying
between or across ceiling joists instead of being hung a few feet above ?

Any ideas as to do/not do it that way ?

I'm not saying it's not done, but i have never seen duct "hanging" in an
attic. Unless you were going to gain a little space, I don't see why
anyone would go to the trouble......

On Mon, 2 May 2005 21:09:38 -0400, "MC" wrote:

I have a question about proper running ductwork in attic.

I have had someone tell me best to have ductwork in an attic next to and
even run between ceiling joist when possible and have the installation blown
in on top instead of having the ductwork hanging from several feet above the
joists. Said that even with insulation wrapped around the ductwork, the
heat/cold in the attic will eventually seep into the duct and will get a
blast of unheated/hot air out when first comes on. By having the duct as
close to the living space when possible and insulating as much on top of the
ductwork keeps the heat/cold loss to a minimum.

I can see where this may make sense, But is this done in any real
installations or would be praticle. I have seen somewhat both ways of being
done, not so sure if that was intended when I have seen the ductwork laying
between or across ceiling joists instead of being hung a few feet above ?

Any ideas as to do/not do it that way ?

Thanks,
MC


I agree with him.

About 1700 homes in my neighborhood have all the ductwork hanging
from the rafters.

one of my rentals was like that. when i put central ac in, i had to
stack 2 feet of insulation around the intake up there to get it to cool
the house.also 2 power vents . ill say one thing for the setup, its
quieter than the intake in the wall.. lucas

MC,

If you ever have to work on or modify the ducts, it is nice to have it
hanging. (But WELL supported.)

With a heat pump and R-6 ducts in the attic, here in South Ccarolina,
the heat loss in the heating cycle is 5%. The heat gain in the summer
(cooling) is 10%. Source: ACCA Manual J, 7th edition.

Hang it up so it can be serviced. Also, if you bury it, depending on
the vapor barrier, sometimes the ducts can sweat, which can cause
problems as well.

(Paul, I know there is a snide remark coming, so let 'er rip.)

Stretch

Well, The house was one of the ones several years ago before Georgia got
stricter on builders that was the run of the mill redneck built, anyone with
a hammer was building houses, only needed to have a business permit and some
may not have had that. Everything done about as cheap as it could have been
and they called it custom built ?

About half of the ductwork was a flex type with a plastic covering that
completely disintegrated in most places and the insulation is starting to
come undone despite my attempt to rewrap and tape into place.

I am adding another room on, The Furnace/AC needs replacing so I am just
getting advice on how the new unit should be installed, I have done some
HVAC work in the past but not much on the duct work part.

Thanks for the info, any additional comments welcomed.

MC

wrote in message
...
one of my rentals was like that. when i put central ac in, i had to
stack 2 feet of insulation around the intake up there to get it to cool
the house.also 2 power vents . ill say one thing for the setup, its
quieter than the intake in the wall.. lucas

Use the foil /mylar covered flex to replace the old flex. Use at least
R-6 flex, R-8 If available. Flex duct should be sized at least 1 inch
bigger in diameter than sheet metal to pass the same amount of air.

Seal ALL connections with mastic and fiberglass mesh tape, NOT duct
tape.

Stretch

"stretch" wrote in message
ups.com...
Use the foil /mylar covered flex to replace the old flex. Use at least
R-6 flex, R-8 If available. Flex duct should be sized at least 1 inch
bigger in diameter than sheet metal to pass the same amount of air.

Seal ALL connections with mastic and fiberglass mesh tape, NOT duct
tape.

Stretch


This is Turtle

Stretch , is that 1" Bigger flex duct than sheet metal duct sizes. Is this a
ruff estimate or close to facts ? Not a loaded Question here !

TURTLE

Shut Up Paul !

Turtle,

The resistance to air flow is higher with flex due to corrugated inside
surface in flex VS smooth surface with sheet metal.

ACCA sells a ductulator (duct calculator circular slide rule with
scales for: Sheet metal, flex, duct board, lined sheet metal). Check
out the same air flow with the same static; the flex will be one size
bigger than sheet metal. The above ductulator is $45.00 to non members
like me.

Just bought one because I lost mine. Bought it at their online store.

Stretch