I recently moved into a new construction home built in 2023, and an HVAC technician informed me that my static pressure is high at around 0.9. Upon inspecting the cold air return holes in the stud walls, I found that they were all cut to 10"x3". In my 800 sqft great room, there's only 1 cold air return, which didn't seem normal to me. So, I expanded the hole to 14"x7" and increased the return grille size from 160 sq inches to 276 sq inches. However, even after this change, the static pressure on the return side barely changed. I'm wondering if my calculations for the CFM make sense. Here's a quick breakdown of my findings:
- Great Room (800 sqft): 421 CFM (14"x7" return and four 6" supplies)
- Front Room (100 sqft): 120 CFM (14"x3" return and one 6" supply)
- Bedroom #1 (130 sqft): 0 CFM (10"x3" return and one 6" supply)
- Bedroom #2 (140 sqft): 80 CFM (10"x3" return and one 6" supply)
- Bedroom #3 (144 sqft): 80 CFM (10"x3" return and one 6" supply)
- Primary Bedroom #4 (272 sqft): 80 CFM (10"x3" return and four 6" supplies)
In total, this gives me 781 CFM compared to the 1,600 CFM needed for a 4 TON unit. I'm worried that I'm missing something important regarding the HVAC setup. Should I be adding more supply vents, or perhaps a return vent to the great room? Any insights would be greatly appreciated!
2 Answers
It sounds like you might be measuring based on the size of your ducts rather than actual airflow. Just a heads up, the bottleneck is often the return duct size rather than the room size. If you're assuming your 10"x3" returns are allowing 80 CFM, that could definitely be an area where you're limited. You could benefit from measuring actual airflow, as it could give you a better idea of how well your system is performing.
You definitely need to think beyond just room size when checking your HVAC. The pressure drop and actual CFM can vary quite a bit depending on your ducting and how many return vents you have. It might be worth looking into adding more supply vents in your great room, or even a return vent to help with the airflow. It all adds up!
Totally agree! More supplies could really help balance everything out. It's all about making sure the system can breathe properly.
Yeah, I would recommend measuring the airflow if you can. It's always better to have actual data rather than just estimates. With joist panning, the entire joist cavity can help, but it's all about the effective area of your returns too.