Upstairs AC unit can't keep up on these hot days

Mac5005 said:
without all the data, my initial bet is on minimal insulation on ductwork and air handler in unconditioned attic, on a system that was likely not pressure tested and or actually sealed.

Meaning so much loss thru the ducts themselves makes the cooling ineffective upstairs. That loss being from air leakage and minimal insulation.

TLDR: donā€™t put air handler and ductwork in unconditioned attic space. Envelope of the living space or in conditioned portion of attic space.
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I have only a single story ranch but it is built on a slab so the ductwork is in the attic which gets full sun most of the day. The system is many decades old so I had to split open the insulation wraps and tape seal many joints to eliminate losses. I did a thermal scan with a borrowed infrared camera one winter to identify where I had leaks. I also bought a pile of the newer duct insulation with the radiant barrier to shield the ducts and started putting radiant barrier in the attic to cut down on thermal soaking. Then for two underperforming areas of the house I spliced in duct booster fans to help even out the airflow. Overall I have the house fat more even and comfortable than it was years ago.

When I did an addition on the house years ago I did the manual J calcs to figure out where the house was when I bought it (no wall insulation, barely anything in the attic) and where it was at the time (R-20 walls, R-30 in half the attic, R-60 the other half) and found that my system was actually a lot larger than it needed to be for how much better the house was. Unfortunately this does not translate to all address of the house being comfortable so I had to do the aforementioned fixtures in the attic to get it better.
 
awheelterd said:
His brother built his house šŸ˜‚
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Be Quiet Season 2 GIF by Martin
 
Had another company come out and check out my system. Tech hooked his guages up and told me that my expansion valve wasn't working properly. Coil temp was at 60 and should've been 40. Got that replaced under warranty and I'll say the upstairs is the most comfortable its ever been. Haven't had a mid 90's day since then to really see how it handles the heat, but I can definitely tell a difference...you can walk upstairs and feel the air is cooler than downstairs for once.

Also, none of the seams on the return ducts are sealed so I'll be doing those as well to hopefully help with any hot air infiltration that might be happening.
 
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