I'm in Central IL, currently just using this furnace in the winter so temps are anywhere from 0 to 40 degrees (can vary by the minute lol)

2 Story house with attached garage. This furnace is for the garage only, 30' x 36'

Goodman 96 efficiency, can't seem to locate a model number. If needed I can get a picture or look harder for model number

Natural Gas.

Honeywell internet connected thermostat

So I let a guy I know from the bar put this in for me. He's got some experience but I don't think a lot, I figured it's just a garage furnace and I could make changes if I need to but he did most of the hard work

So here's the problem. It has one large air return (16x25 filter) and then 2 supply runs that each has 3 registers. The first register on the shortest run is getting the vast majority of the air flow. The next two down that run get less but more than any of the 3 on the longest run. I have a feeling this is due to incorrect size of ductwork, which is insulated flexible ducting.

What can I do to equalize this out better?

 

Put a damper in the shortest line or put adjustable registers on.

The model number will be on an ID tag inside the furnace on the sidewall near the burner.