The weather has been pretty warm lately so we've been running our A/C. I noticed that it didn't seem like much air was coming out of the registers, so I checked to make sure the blades/louvers were fully open. When I pulled out the register there was a HUGE difference between having the register in (and completely open) and removed. There is easily 40% more airflow when the register is removed.
We have a few "scroll pattern" registers that are a bit better, but I haven't been able to find them locally anymore. All of the new ones seem to use this plastic louver behind the decorative plate that looks like it blocks 50% of the air even when fully open.
Are there high-flow registers available (4x10)?