How much cfm do you lose when a 90 Degree elbow is used on a squirrel cage blower?

[Bruce L]

Just wondering if there is an exact calculation for how much cfm is lost when a 90 degree elbow is used for this type of fan, I don't think the high pressure (aof) blower would be as much of an issue?

[Waynehere]

Actually, if you talk to any HVAC tech out there or someone that has put in heating and AC systems, 90's are a killer. If you have to have any in your system, you always try to make them as long of a sweep as possible. 2 45's are way better then any 90. You can google this and see what I mean.

[maple flats]

Waynehere is right. While I no longer have the charts there is a substantial loss with a 90 ell on squirrel cage type fans. Back in my heating days I had charts. It depended on CFM and cross sectional area. Doing 2 45's are far less loss.
I never dealt in high pressure so I had no charts for that but I suspect as Waynehere says, it is less.
On my 3" outlet HP blower I have 3 long sweeping 90 degree ells of 4" PVC before that splits into 2 @ 3" each. The force is still good but I have no way to determine what I lost.

[sams64]

To calculate the loss you will need to know the velocity through the elbow. This will let you calculate the pressure increase fromt he elbow. Then you need a chart for that fan that shows the flow at a given back pressure level.

sam