Register and Diffuser

[retina90eye]

I am currently resarching on a project trying to find out what is the single most used size of sidewall register and floor diffuser installed in homes:

1. Homes more than 30 years old
2. Homes less than 30 years old
3. Apartments
4. any regional differences? (ex: East Coast vs the Mid-West)

Thanks for answering.

[PPS]

While I doubt you won't get anywhere on these questions, you could always try contacting a major grill manufacture and ask what are there most popular sizes. Try Ameriflow for starters.

Then try several associations within the HVAC trades (Google search). I doubt there will be any real answers (the grill manufactures won't want this info to fall into the hands of their competitors and the contractors probably don't keep detailed records.