flexable heating duct

Posted by 58dotneck on November 28, 2008, 9:02 pm

I have a family room built on a slab. The 8" metal duct from the basement
is the farthest from the furnace. Air flow and temp. are low. A duct
booster fan helped with flow but not temp. obviously. Can I run an
insulated 6" duct through the 8" concrete duct and insulate the rest of
the metal duct in the basement? Or would that increase temp. and reduce
flow? The concrete duct runs about 12ft. to the first register and about
15ft. to the second.

thanks
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Posted by Noon-Air on November 28, 2008, 9:25 pm

> I have a family room built on a slab. The 8" metal duct from the basement
> is the farthest from the furnace. Air flow and temp. are low. A duct
> booster fan helped with flow but not temp. obviously. Can I run an
> insulated 6" duct through the 8" concrete duct and insulate the rest of
> the metal duct in the basement? Or would that increase temp. and reduce
> flow? The concrete duct runs about 12ft. to the first register and about
> 15ft. to the second.
> thanks

ok
ok
ok
not good
no
no and yes
ok, ok

Do this... Do a complete set of Manual J and Manual D calculations, then use
your flow hood to verify the airflow returning to the furnace, and the
airflow coming from each vent. The resulting measurements should be
reasonably close to the calculations. If the're not, then you need to
re-design the ductwork accordingly then re-test after the work is completed.
When your done, if everything is right with the world, the furnace will be
quiet, you shouldn't hear any air noise...or very little, and there should
be no more than a degree and a half or so temp difference between any 2
rooms. If you don't understand what I have written, then you either need to
go back to school, or pay somebody that actually knows what they are doing.

--

Steve @ Noon-Air Heating & A/C

"Stop calling me for freebies Satan,
I'll fix your air conditioner when you pay me, Cheapskate!"

Posted by Douglas S on November 30, 2008, 9:06 am

Let's step back a second - why is the air cold? Well the cold
concrete is sucking the heat from the air.

Why is the concrete cold? Lack of perimeter insulation around the
slab.

Check around the exterior of the slab for insulation board. If it is
not there, you need to dig a 2 ft. deep trench around the slab and put
2" thick blue board around the slab. Make sure you clean off the
concrete before applying adhesive to the concrete (you will want to
glue the board on to prevent air gaps between the insulation and the
foundation - this could create a convective heat loss when you are
trying to prevent a conductive heat loss). Make sure you compact the
soil when you back fill.

Posted by Zyp on November 30, 2008, 5:12 pm

Douglas S wrote:

> Let's step back a second - why is the air cold? Well the cold
> concrete is sucking the heat from the air.
> Why is the concrete cold? Lack of perimeter insulation around the
> slab.
> Check around the exterior of the slab for insulation board. If it is
> not there, you need to dig a 2 ft. deep trench around the slab and put
> 2" thick blue board around the slab. Make sure you clean off the
> concrete before applying adhesive to the concrete (you will want to
> glue the board on to prevent air gaps between the insulation and the
> foundation - this could create a convective heat loss when you are
> trying to prevent a conductive heat loss). Make sure you compact the
> soil when you back fill.

Actually;

Find a competent energy audit company in your county and have them do a
thermal image of the slab. You'll find that likely there's either no edge
insulation or at the very least you'll find heat leakage. The energy audit
will at it's very least give you suggestions on how to tighten up your home
and / or improve your HVAC as well as the pay-back timeline.

If you aren't really ready to inve$t any money here, then your family's
comfort is not that important to you. If you don't like the answer to your
question, I'm sorry....

--
Zyp

Posted by Zyp on December 1, 2008, 2:54 pm

ftwhd wrote:

>> Douglas S wrote:

>>> Let's step back a second - why is the air cold? Well the cold
>>> concrete is sucking the heat from the air.
>>> Why is the concrete cold? Lack of perimeter insulation around the
>>> slab.
>>> Check around the exterior of the slab for insulation board. If it
>>> is not there, you need to dig a 2 ft. deep trench around the slab
>>> and put 2" thick blue board around the slab. Make sure you clean
>>> off the concrete before applying adhesive to the concrete (you will
>>> want to glue the board on to prevent air gaps between the
>>> insulation and the foundation - this could create a convective heat
>>> loss when you are trying to prevent a conductive heat loss). Make
>>> sure you compact the soil when you back fill.

>> Actually;
>> Find a competent energy audit company in your county and have them
>> do a thermal image of the slab. You'll find that likely there's
>> either no edge insulation or at the very least you'll find heat
>> leakage. The energy audit will at it's very least give you
>> suggestions on how to tighten up your home and / or improve your
>> HVAC as well as the pay-back timeline.
>> If you aren't really ready to inve$t any money here, then your
>> family's comfort is not that important to you. If you don't like
>> the answer to your question, I'm sorry....

> He's likely to wear out his dialing finger finding someone who has a
> thermal imaging camera. Do you have any idea how expensive they are?
> Perhaps you could provide a number for him to call.

Yes;

They are expensive. So is training. So is the vehicle's, tools, and all
that crap. Thermal imaging camera's start around $4995.00 and go up
depending on resolution. Air hoods start at $1999.00 and go up from there.
Duct blaster equipment starts around $2050.00 for the package and goes up
from there. Blower Door Systems start at $2525.00 and go up from there.
What's your point? Either you are an energy audit professional, or you are
not. Either you want an answer to your problem [meaning the original
poster] and the solution or you don't. To generally get an answer, at least
from my company, it starts at $550.00 and goes up from there. That'll get
you about 3 - 4 hours of inspection work and an Energy Pro audit.

--
Zyp

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