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Old 01-05-12, 04:13 PM   #12
abogart
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Well I don't see the ductwork getting upgraded any time soon. The house is at least a century old and the 6" supply ducts all kind of spider out from the furnace in the basement, with a short plenum in either direction. The return ducts are made from metal sheeting between two large boards, just below the floor joists. Many of the ducts feed two registers, one downstairs and one upstairs. Some, however, run straight from the supply plenum to the main floor. Those are mostly the ones that I have reduced or closed the dampers on.

There are four main rooms on the east side of the center wall on the main level (2 living rooms, dining room, family room), each with at least one supply on the inside wall, and one large return on the outside wall, with the exception of the front room which has a non-functional (decommissioned) return. Each downstairs room except for the dining room has an adjoining room on the west side of the center wall (kitchen, bath, study) which each have a supply register but no return. Basically, all of the returns are on the east side of the house, and all of the supply registers are on the west center wall, or west outside wall. The upstairs has no returns, but there are supply registers in each of the 5 bedrooms and 1 bath.

In the basement there are 3 return ducts measuring roughly 8" x 24" each. I'm no HVAC contractor, but it seems like these should provide adequate return airflow for a 100k furnace. The fact that there are no returns upstairs, however, makes for some unbalanced airflow issues. I think you can understand why I would have to close the damper on a short duct that feeds a register on the main floor, and open the damper on a long duct that feeds a downstairs register and an upstairs register. So basically I have been doing this careful balancing act of dampers trying to cut airflow to rooms that get too much air, and boost airflow to rooms that don't get enough air. I guess I always assumed that the blower was going to put out the same amount of air regardless of how much came out of each register. The way I have it set now, 5 of the downstairs ducts that lead to main floor register vents are either fully or mostly damped off, or closed at the register. Each room seems to maintain approximately the set temperature, when all doors are open.

Last edited by abogart; 01-05-12 at 04:20 PM..
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