I'm replacing a non-functioning draft inducer on the Goodman furnace in my house (GMP075-3). The previous inducer was mounted with a sheet metal back plate between it and the wall of the furnace. This back plate happens to cover the 3.5" draft hole on the wall of the furnace with a smaller 1 5/8" hole of its own (see pictures) which I happen to find odd. Wouldn't that restrict air flow?
Since the new inducer assembly didn't come with a back plate, I'm wondering if the back plate is actually necessary. The inducer being replaced was new as of 2009 so I'm suspicious that perhaps this smaller hole somehow restricts airflow thus causing strain on the inducer motor which led to a failure after just 3 years. On the flip side, perhaps the smaller hole is necessary because it plays some role in protecting the fan blades from being overexposed to high temperatures via the larger 3.5" draft hole.
Any help from an expert would be much appreciated. I assume the plate is necessary but want to be sure I'm not going to need a new inducer again in 3 years.
The Inducer Assembly
The back plate and/or mounting bracket with 1 5/8" hole.
The inducer assembly with back plate in position (covering most of the open fan space)