Squirrel cage fan is going to run at a higher RPM when it's out of the housing because the housing directs the air to the vanes and to the outlet. Just running it out in the room like that doesn't apply any air load to the vanes. If you think the blower is running faster when it's in the housing you should check for obstructions at the air supply inlet. Analogous to blocking inlet air on your shop vac with the palm of your hand causes the blower to speed up by eliminating the air load on the vanes.