Heating and air conditioning

Author

Poor ductwork?

Murdentech

2006-03-11, 9:21 am

<snip OP>

Good that you did some homework and contacted someone in the business that
you trust... however, it sounds like you have ductwork problems.

Even if you change the equipment and do not address the ductwork problems,
you will still have high bills. Your systems are in the attic... that's the
first clue. Your systems were installed by the builder on the cheap...
that's the second clue. Your utility bills are outrageous... that's the
third clue.

If you have the actual amperage draw taken on an operating system, you can
calculate the cost per hour. If your systems are running excessively, that
points to problems in either equipment sizing or duct design. Duct loss in
an attic system can be tremendous.

Even a well ventilated attic can be over 120º in the summer. If your attic
is not unbearably hot on a sunny day, you are probably air conditioning the
attic.

Blower fans should be on high speed for cooling. A single badly designed or
layed out duct transition can cost you hundreds a month by causing the
system to run excessively. Attic ductwork should be sealed and insulated.
*Flex duct should be avoided at all costs.* Bends and turns need to be kept
to a minimum on both supply and return ductwork.

You have to take temperature measurements at supply and return grills, you
also have to take supply and return measurements at the units to determine
duct loss. Further, you should have velocity and CFM readings taken at
supply and return grills to make sure there is adequate air flow into and
out of the rooms.

You are warmed up for the HVAC shopping race, but you are not out of the
gate yet... spend a couple hundred having the ductwork investigated and
improved before you throw thousands into new equipment.

Jeff Murden

gofish@gonefishin.net

2006-03-11, 3:21 pm

On Sat, 11 Mar 2006 12:42:21 GMT, "Murdentech" <j. murden @ insight
bb.com> wrote:

>
><snip OP>
>
>Good that you did some homework and contacted someone in the business that
>you trust... however, it sounds like you have ductwork problems.
>
>Even if you change the equipment and do not address the ductwork problems,
>you will still have high bills. Your systems are in the attic... that's the
>first clue. Your systems were installed by the builder on the cheap...
>that's the second clue. Your utility bills are outrageous... that's the
>third clue.
>
>If you have the actual amperage draw taken on an operating system, you can
>calculate the cost per hour. If your systems are running excessively, that
>points to problems in either equipment sizing or duct design. Duct loss in
>an attic system can be tremendous.
>
>Even a well ventilated attic can be over 120Âº in the summer. If your attic
>is not unbearably hot on a sunny day, you are probably air conditioning the
>attic.
>
>Blower fans should be on high speed for cooling. A single badly designed or
>layed out duct transition can cost you hundreds a month by causing the
>system to run excessively. Attic ductwork should be sealed and insulated.
>*Flex duct should be avoided at all costs.* Bends and turns need to be kept
>to a minimum on both supply and return ductwork.
>
>You have to take temperature measurements at supply and return grills, you
>also have to take supply and return measurements at the units to determine
>duct loss. Further, you should have velocity and CFM readings taken at
>supply and return grills to make sure there is adequate air flow into and
>out of the rooms.
>
>You are warmed up for the HVAC shopping race, but you are not out of the
>gate yet... spend a couple hundred having the ductwork investigated and
>improved before you throw thousands into new equipment.
>
>Jeff Murden
>

Nice post Jeff.

Fact of life: sheet metal ductwork is quite common on the east coast,
flex ducts are the norm on the west coast.

Flex duct isnt the problem, the problem is the typical way they're
sized & installed.

Too bad he's not in Ca., the new Title 24 energy code here mandates
ALL ductwork insulated to R-8 minimum.

Another kicker is: any furnace, coil, condenser or HX changed out
requires a mandantory duct pressurization / leakage test. Maximum
leakage rate for an existing system is 15% of total system cfm. Any
new install is 6% leakage rate. System cfm based on 400 cfm per ton.

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