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Question DetailsAsked on 9/7/2015

my duct work is to small for my house , needs to be replaced with new duct wor and bigger vents

My house was built in the 70's , electric heat pump , I converted it to oil heat, no gas on the street , the vents in my house are very small , need bigger vents , maybe new duct work , I need some one who is exp. with this problem, I realize I will have to remove some flooring , but willing to do the job. I live in Winchester Ma.

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Voted Best Answer

IF your heat pump (assuming still forced air with an air handler unit) heated your house OK even if the balance was off), then your ducts are likely big enough - may need some adjustment of airflow split. As I read it, maybe the heat pump was OK but the new furnace is not cutting it - which would likely mean it is undersized, needs a larger capacity fan, or such if using the same ducts as the heat pump.

It is possible your registers are undersized - they commonly are far smaller than the duct leading to them so cause unnecessary friction losses, and there are also ones (or add-on deflectors) tha direct the air around the room differently to provide more effective heat distribution.

You need a heating and A/C contractor (or 2 or 3 for comparative bids) who is familiar with system configuration and layout, not just a maintenance tech - to run the ACCA Manual J calculation (to determine the heating/cooling load that the house presents), Manual S (for the sizing of the unit itself which takes into account furnace efficiency and such), then Manual D (duct and register sizing and routing) to assess the capacity and layout and condition of your current system to determine what is the CAUSE of your issue. In many cases minor ducting or register changes, maybe introduction of a motorized damper in the ducts so you have individual thermostat control of two (or more) zones, register adjustment, etc will take care of it much cheaper than the several thousand $ or more new ducting costs.

BTW in normal wood or steel frame construction duct modifications involve opening up ceilings to modify the ducts, rarely floors (except as needed to put in new or larger registers), and between house levels some wall openings if floor-to-floor ducts have to be run.

Answered 4 years ago by LCD

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