My house is 2300 square feet - a two story. Problem is that the crawl space under the house is an average 12 inches high. Some spots lower and some higher. I have unfinished attic space above on the second floor. Only one closet in the downstairs and it's already got the water heater and fuse panel.
My question is - would it be possible/practical to do a High Velocity system for the downstairs and a conventional for upstairs? Should you mix them in the same house?