So a bit of informational backstory as to all of the different parties involved in our Bonus Room cold issue. Ryan Homes is the builder. They had an engineer design the HVAC system based on the design of the house, which as part of that design has certain expected CFM values per vent to make it work as designed. This is then installed by the HVAC subcontractor upon build (Sobieski in our instance), and verified by a third party Energy Star inspection company (PEG Environmental). As part of our service request, since this is a continuing issue Ryan wanted to bring out PEG to inspect everything again before having the HVAC contractor try some more dark magic to fix the problem.
Fast forward to yesterday when the fine folks at PEG Environmental (actually an independent subcontractor hired by them, who in turn was hired by Ryan) came out and did a re-balancing of our vents in the house. Most of them checked out AOK and some had a few tweaks. I then showed my wonderful makeshift two sensor thermometer in the Bonus room reading 6 degrees colder than the thermostat at about 4-5ft and a whopping 14 degrees colder at the floor. The PEG guy had an idea about why it was cold, and set up a blower test.
The blower test actually creates a negative air pressure inside of your house, which makes it easy to feel where the drafts are entering your home. Thankfully he offered to do this, because it showed that the cold air was blowing in along the bottom of the walls under the baseboard. Since those walls are kneewalls, and there is space behind them to allow the airflow for the roof to work correctly this makes sense. The kneewalls itself were insulated but there was no sealant for the interface between the kneewall and the floor. The HVAC system was fighting a losing battle between the hot air it was pushing into the room from the top vs. the cold air drafting in from three sides on the floor.
The gentleman then reported back to my service rep at Ryan what he found, and they're going to try and foam seal along that frame, which involves pulling up the carpet and removing the baseboard to get in there. Hopefully this will alleviate the problem, and I'll be sure to add another follow up when its completed.