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Within the last year I had a new HVAC unit installed in my historic home. I was able to use much of the old ductwork but tied in to a lot of the existingstuff as well.

The problem: I have hardly no flow in three registers. Of course I will investigate blockage and so on. I am concerned about distance from the main unit. Is there a prescribed distance from the main unit that should be maintained?

I will have to deal with what I have but would appreciate any thread that addressing increasing air flow within certain parts of the home/troubleshooting ductwork.

thank you.

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It sounds like no one bothered to design your ductwork. You can't just run a bunch of ducts to a bunch of places and then expect to control air flow with dampers. I just doesn't work that way. The duct system itself has to be designed properly or you'll never get adequate flow to certain locations.

I suggest hiring an HVAC contractor who's been trained in duct design. Ask him to evaluate your existing duct system and determine whether or not it can be salvaged.

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Without knowing more, I'm betting you still have the original gravity duct system.

Are there big (12"-18" diameter) ducts in the basement, or duct boots of that size? Are the supplies on interior walls, behind doors, or located in weird locations? Is there a big return at the bottom of the stairs?

If yes to any of these questions, you're working on an old gravity system. They don't transition to modern equipment particularly well.

It's not uncommon to have some of those old ducts literally falling apart and rusted away in the walls; you may be conditioning the stud cavities instead of the rooms.

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