Aeroseal Tech Inc.

I found my second floor was way colder than the main floor in the winter and way hotter in the summer. Air flow from vents was poor, so I called Victor and he came by at a time convenient for me (after dinner which was nice) to see if they would be able to solve my problem. He was almost 2hr late, but clearly demonstrated where I had leaks in the duct system. Victor took baseline measurements and showed me what their process could do and answered all of my questions well.
We scheduled a date to do the work. He again arrived 1hr late, but got to work quickly and the whole process took a little shorter than expected which was nice (your house will vary though). They cleaned up neatly and Victor took the time to show me all the measurements from my vents compared to before, which were impressive.
I am extremely pleased with the work. Got 97% reduction in leakage and doubled the airflow from my vents. This largely solved my issue of temperature variances throughout the house. My Nest tells me I'm using my furnace at most half as much as before to maintain the same comfort level, so I'm saving a ton of energy costs too!

Pro tip: expect to air out your house after sealing is complete as the sealant still gets into the air from the gaps in your ductwork (part of the process). I had a large gap in the basement which caused a lot of sealant to escape. I was assured its non-toxic but I it smells funky and you still don't want to be breathing that, so you'll want to air it out.

It's pricey, but you'll live more comfortably for less on your energy bill. Thus everyone should get their ducts sealed and I would recommend Aeroseal tech to anyone.