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airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8385
Experience:  Furnace, A/C and heat pump specialist.
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I'm remodeling a home built in 1960 that appears to have

Customer Question

I'm remodeling a home built in 1960 that appears to have a retrofitted hvac system. The plenum feeds 2 large flex pipes that each feed their own supply duct. Each of those supply ducts feed an insulated/enclosed dropped ceiling that has 4 registers that feed the surrounding rooms (1 register to each room). I've removed the drop ceiling and need to re-direct the flow to the surrounding rooms. Can I just remove the existing supply duct and branch off the flex pipe to supply each of the surrounding rooms?
Submitted: 1 year ago.
Category: HVAC
Expert:  airheatman replied 1 year ago.

Absolutely, We need to know the cfms of unit (Can be verified by model number) and the size of the existing ducts to properly size any new ducts though.Foe example a 12 " duct will carry approx. 800 cfms so we could run 4 seven inch ducts off of it without losing velocity.

Customer: replied 1 year ago.
Ok I will measure this evening. Is it measured by the outside diameter?
Expert:  airheatman replied 1 year ago.

Inside of duct.

Customer: replied 1 year ago.
The rooms don't appear to have return registers, is that normal?
Expert:  airheatman replied 1 year ago.

As long as the air can circulate back that is normal. If doors do not have a gap underneath, you want to consider trimming bottom of doors or adding grilles so air can circulate when doors are closed.