jmic

Here's the situation. I'm in the process of adding on approx 2300 sq. ft. addition to my existing 800 sq. ft. house. The new addition ceiling height is 18" higher than the existing house ceiling. The heat exchanger is going in the new addition on the second floor so the ductwork has to go up approx. 4' then travel approx. 16' and when it reaches the existing house attic it will have to angle down 18" to be on the top of the ceiling joist of the existing house and then travel approx. 18' where it will then terminate, from there along that 18' run will probably have 4 runs of flex to the registers for the ceilings below. Thats the senerio, here's the question. Since heat rises how much efficiency will I lose with that drop in the duct work if any. Thanks
Joe

Bestheating

Your question of warm air rising is correct. If you had a gravity fed furnace of 100 years ago, I would be concerned. Today we use the forced air systems to level the playing field. Some thoughts to consider: First, the trunk lines and equipment will have to be sized to allow for the volume (read cubic feet of space, not square feet) and anticipated BTU requirements. Second, you will want to make sure and insulate any ducts in uninsulated areas. Flex at the end of the trunk lines will tend to restrict what flow is left that far from the equipment. The transitions in the trunk line, are better done in 45's than 90's. Up or down is not of particular consiquence.
I would really recommend some time with a duct person as being well spent. Get these plans underway, as you will want the home roughed in for ductwork as soon as the framing is getting done. And above all else, remember the return airs. Lot's of them. Especially from the more distant areas.

jmic

Best,
From the replies I see on this Thread for HAVC verses the views I see this is like a Maytag repairmen (very lonly place). I thank you for your response and will continue my diligent research to make this aspect of my project a success. Have a great Holiday Season!
Joe

locofoco

Best is right on. If I were you I'd get a duct designer to size the duct, unit, diffusers,etc. It will be a job to fix after the drywall is up. I was an hvac field grunt, designer, estimator, and superintendent before retiring and getting into remodeling. Additions like you're describing are always tricky.
loco