2008 xl heater

[Doubeleive]

Doubeleive, I found one for sale like the picture I posted here and it appears to be like your right picture but with the long cooling (?) duct missing. Does that make sense?
It is the part number that GM parts sites list for mine but mine has the short duct like your left picture.
Would the right one on your pictures would properly without the cooling dict?

You might be able to transfer the cooling duct over from your old one not sure

 

[EddieC]

You might be able to transfer the cooling duct over from your old one not sure

I tracked down the current part number for my Tahoe on both GM parts sites and Rock Auto and RA had the clue to why there is a hole. There was a link to recommended auxiliary part; a replaceable long cooling tube like you showed on one of your pictures. The issue could be that my original fan has the integral short cooling tube, so, as you mentioned, clearances could be an issue with the long tube.

 

[EddieC]

Doubelieve,

In the blowers that you have had did you notice any play in the blower in the direction of the shaft length (in and out play of the shaft in the motor)?

I got mine out and cleaned the caked on dirt off the fan blades and noticed the shaft moves in and out of the motor enough to notice. It's like setting solid lifter valves at a few thous by feel. There is no lateral movement, just in and out. Curious if that is normal.
Putting it back in there is a ticking at slow speeds and an occasional complaining (lost for words) at higher speeds. Previously I noticed the "complaining" on the road if I turned the truck a particular direction listing the body.