Double Checking Duct Sizing

Old 11-27-16, 07:12 PM
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Double Checking Duct Sizing

I ran the numbers for my room size and wanted to double check my figures. I have 4 rooms with the following sizes:

16x11x9-1 exterior wall, 1 wood frame, single pane window
15x21x9-all interior no windows
18x13x7-2 exterior walls, 3 wood frame, single pane windows
21x18x12-2 exterior walls, 5 wood frame, single pane windows

All of the rooms will have r13 insulation (biggest that will fit in the studs I have) in walls and r30 in the ceiling. The furnace size I got was 80,000 btu at 95% efficiency which would cover by 4,000 btu roughly. The room that is currently being redone is the 21x18x12 which requires 3 90degree bends to get to the furnace at a run of 45 feet. The numbers I got were 529.2CFM needing 14" flex duct. The house is in Iowa and its a 1.5 story high room (house is late 1800's built). Does that duct size seem right? It seems a bit high to me but thought I'd double check myself.
Old 11-29-16, 01:47 PM
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Did you do a load calculation on these room or how did you come up with the sizing?

What are you trying to do? Do you have an existing heating system that you're trying to extend to a part of the house with no heat?

Any chance of upgrading the single pane windows or at least shrink wrapping them?

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