Correct Duct Size For Bath Remodel

[brb]

I'm remodeling my 1920's 2nd story bathroom. Had some asbestos ducts that were removed to make room for a pocket door in the bath. One duct fed a small 3rd upstairs bedroom and the other fed the bathroom. they were both 2 1/4 X12. The amount of airflow in the bathroom was way to much. I know that there are a ton of variables in how many cfm a room needs. However, doing a rough estimate of the room size and factoring in a air change of 6 times per hour, the bathroom needs about 34 cfm (its small 7x6). The adjoining bedroom is only needing about 70 cfm.

The supply lines from the furnace are 6in round. I am debating on what to run up to these vents. It seems like everyone has a different opinion on this. This would be running through a wall. The wall could be made into a 2X6 wall but is 2X4 at this point. There is a 4ft 6in pipe out of the furnace to where it goes up 100in through the wall and then would need to take a 90 degree bend to go 72in to another 90 degree up to the stack head.

Should I run one large vent and share the flow between the two room with a double stack head or run two oval pipes, one to each room? I think I would need a 5in oval for the bath and a 7in for the bedroom. Also, the bath will have proper insulation compared to the nothing that was there previously.

Thanks, for any input.

 

[Havoc/r]

I'm remodeling my 1920's 2nd story bathroom. Had some asbestos ducts that were removed to make room for a pocket door in the bath. One duct fed a small 3rd upstairs bedroom and the other fed the bathroom. they were both 2 1/4 X12. The amount of airflow in the bathroom was way to much. I know that there are a ton of variables in how many cfm a room needs. However, doing a rough estimate of the room size and factoring in a air change of 6 times per hour, the bathroom needs about 34 cfm (its small 7x6). The adjoining bedroom is only needing about 70 cfm.

The supply lines from the furnace are 6in round. I am debating on what to run up to these vents. It seems like everyone has a different opinion on this. This would be running through a wall. The wall could be made into a 2X6 wall but is 2X4 at this point. There is a 4ft 6in pipe out of the furnace to where it goes up 100in through the wall and then would need to take a 90 degree bend to go 72in to another 90 degree up to the stack head.

Should I run one large vent and share the flow between the two room with a double stack head or run two oval pipes, one to each room? I think I would need a 5in oval for the bath and a 7in for the bedroom. Also, the bath will have proper insulation compared to the nothing that was there previously.

Thanks, for any input.

Run two stacks

 

[Sponsor]

 

[Stuff]

Two. Remember to add dampers to each feed.

 

[brb]

Thanks guys. I thought that was probably the best thing to do. Can i run the 5in oval right on top of the 7in or do they need to be separated?