Air Conditioning - Basement Ductwork redo

I have a 90 year old house. Years ago when it was converted to a forced air setup, ductwork was run around the entire perimeter of the basement (30x28) or 120ft of duct. It blocks the windows and basically looks like too much duct for this house. I am thinking about running a main duct horizontally across the basement and feeding the vents off that much shorter duct.

Will I be reducing the flow of my heat and airconditioning or increasing it?

Any help would be greatly appreciated!

should have put this under Ducting Systems and Air Ventilation.

I have a 90 year old house. Years ago when it was converted to a forced air setup, ductwork was run around the entire perimeter of the basement (30x28) or 120ft of duct. It blocks the windows and basically looks like too much duct for this house. I am thinking about running a main duct horizontally across the basement and feeding the vents off that much shorter duct.

Will I be reducing the flow of my heat and airconditioning or increasing it?
Any help would be greatly appreciated!
The data you must have is your heat-gain and heat-loss for each room using Manual J calculations.

The help U need is someone to do a Manual J load calc for each room & then do a Manual D on the duct system design layout.

There is little chance U will have all the tech info & know-how skills to do those two jobs correctly.

It may also be difficult to find HVAC contractor's that will do those things properly.

There is a good chance you will have a more balanced, efficient, & higher delivery of airflow to all rooms, with more efficient heating & cooling to all rooms.

The help U need is someone to do a Manual J load calc for each room & then do a Manual D on the duct system design layout.

It may also be difficult to find HVAC contractor's that will do those things properly.



My experience was that contractors don't really do he calculations and thus under size the ducts and oversize the furnace. As a result I bought a manual-j calculator and did my own. I then found some info on CFM needs per room based on the manual-j calcs and used a "ductulator" to calculate CFM per duct size at a give WC of friction. Really the math wasn't that hard but learning the terminology was.

I did not find any real exact manual-d freeware but did find some forum posts from people who were supposedly quoting a manual-d book regarding the CFM needs based on a room's given heat loss/heat gain value.

Would love to know if anyone has good manual-d info they could share so I could double check my calculations before installing the ducts.

Those manuals are protected from public access unless you're willing to shell out the money for one.

IMO, that information should be made open to the public.
It is rather involved & few would ever put it to use.

The problem is that is, >can U find a contractor that will do a Manual D.

You can use a larger transition area off the main duct-run to the branch runs, which will reduce the Total Equivalent Length by many feet.

Over-size the Return Air ducts & Grille areas & make sure the Filter Grille is over-sized. You want at least 1-sq.in., of filter area for each 2-CFM.

I prefer 1.5-sq.ins., to 2-cfm; 1200-cfm / 1.5= 800-sq.ins.

800-cfm * .75 for Grille area= 600-Sq.ins.,open air area not counting filter area restriction, etc.

Do a Google search...