Sizing up duct-work

**dismas66** · 07-14-2005, 06:02 PM

I got a small ranch..AC job..
will be installing the AHU in the attic..
I will be adding a 3 -ton unit..

Was wondering how do I figure the Trunk-line...coming out of the discharge on the AHU
the Ranch is 46' Wide

the house is a little under 1400 sq. ft.

thoughts

talk soon
dismas

**dan sw fl** · 07-14-2005, 06:13 PM

Duct layout guidance can only realistically be developed after a floor plan is provided.

... 3-Ton is ~ 1,200 CFM,
... FOR A STARTer :
... AHU outlet duct should be ~1.5 Sq. Feet
... 12" x 18" hard duct at least 6 feet long

Any branches sizing is guessing.
... 800 CFM = 1.0 Sq. Foot ( 12"*12" or 14" diameter )
... 600 CFM = 0.8 Sq. Foot ( 10"*12" or 12" diameter )

Add up all the dP's for straight runs, fittings, outlets on each flow path to assure you have met ACCA Manual D criteria and AHU fan capability.

**dismas66** · 07-15-2005, 10:22 AM

Thanks Dan,

If I can get you the ..floor plan...could you help me out
until ..I can afford the HVAC Software...

I do have the Manual D...but, can't claim to be a pro..at it

I will be having the duct work..made up at the sheet metal shop...so I am trying to be close ..

talk soon
Dismas

**dan sw fl** · 07-15-2005, 10:42 AM

Originally posted by dismas66
If I can get you the floor plan could you help me out until I can afford the HVAC Software

I will be having the duct work made up at the sheet metal shop so I am trying to be close ..

O.K., minimal charge for 1,400 Sq. Feet depending on extent of details needed and permitting documentation required.

Send .PDF file to
racingdan11 at comcast dot net
___________ @ ________ . _____
( /\ address per Forum rules)

OR can you snail mail if you have the time.
OR FedEx if your schedule dictates.

I can complete in < 1 day after all info is provided.

You need to be Nearly EXACT on a REALISTIC DUCT and AHU layout depending on space allocation as required by buidling structure.

or write for other arrangements
+ necessary buidling design details.

1. City, State
2. House Orientation
3. AHU Location: Qty. 1
4. Insulation
R-__ wall .. ceilings
__ Batt
or __ Spray Foam

5. Window schedule
__ Mfg: Anderson or other

6. Wall Height:
_ 8 9 feet
_ 10 feet
7. One story

8. Special internal gains, if any,
i.e. A-V or computer room