I posted this at the end of my original long thread, but thought it might merit starting a new one to get some quick feedback. Sorry for the duplication. (Original thread)
For those of you who don't recall, in planning for my conversion to gas (from oil) I ran my own heat loss analysis a few weeks ago. My contractor now did his using commercial software and they don't agree,
The contractor walked the house with me and I provided construction details, so he had the same (or similar) R values and measurements that I used for my Excel based heat loss calcs. He used Wrightsoft to do his calcs (Manual J 8th Edition).
My original calculations came out to around 55k BTU/Hr. Wrightsoft came up with 76k. (See table)
![]()
He sent me the Wrightsoft report late last night. One thing caught my eye that might explain the discrepancy. 41.5% (31.7k btu) of the heat loss is through "ducts". Remember this is a hydronic system. I do have central AC, but I'd be shocked if the AC ducts are passively losing that much heat (or even 10% of it) during heating season. The AC systems are entirely separate from the heating system, except for one zone that has the fan coil (zone 3) and its own compressor. Hard to believe the ducts for a 400 sf "zone" could lose 41% of the house's heat!
When I look zone by zone, it appears that a standard 41.5% for duct load is applied to all zones.
![]()
Are any of you familiar enough with Wrightsoft to know if there is a setting he should have turned on/off to eliminate the impact of ducts? Or is this a normal outcome?
Thank you again. Obviously a 41% swing in load is a big decision factor!
For those of you who don't recall, in planning for my conversion to gas (from oil) I ran my own heat loss analysis a few weeks ago. My contractor now did his using commercial software and they don't agree,
The contractor walked the house with me and I provided construction details, so he had the same (or similar) R values and measurements that I used for my Excel based heat loss calcs. He used Wrightsoft to do his calcs (Manual J 8th Edition).
My original calculations came out to around 55k BTU/Hr. Wrightsoft came up with 76k. (See table)
He sent me the Wrightsoft report late last night. One thing caught my eye that might explain the discrepancy. 41.5% (31.7k btu) of the heat loss is through "ducts". Remember this is a hydronic system. I do have central AC, but I'd be shocked if the AC ducts are passively losing that much heat (or even 10% of it) during heating season. The AC systems are entirely separate from the heating system, except for one zone that has the fan coil (zone 3) and its own compressor. Hard to believe the ducts for a 400 sf "zone" could lose 41% of the house's heat!
When I look zone by zone, it appears that a standard 41.5% for duct load is applied to all zones.
Are any of you familiar enough with Wrightsoft to know if there is a setting he should have turned on/off to eliminate the impact of ducts? Or is this a normal outcome?
Thank you again. Obviously a 41% swing in load is a big decision factor!