Posted By patonbike on 18 Jun 2015 12:42 PM
Thanks.. Wow I didn't realize there was an FH18... for some reason I had only ever seen the FH9/12/15..  I thought the only 18 was the FE18. 

Still researching, but it doesn't look like the multi head units are less than each individual unit but there should be savings on installation.

There's only  a slight performance hit, but you run into other issues, notably the run-length capacity derating on refrigerant lines, and the minimum-modulated output of the bigger compressor, which can be higher well above the min output of a single head, which means efficiency goes to hell during the shoulder seasons. 

For instance, the FH09 modulates down to 1600 BTU/hr @ +47F with it's own compressor, but tie that onto a 3-ton compressor that puts out a minimum of 7000 BTU/hr or higher, an FH09 head on a multi-split zone will not be able to run in an modulating high-efficiency mode above some outdoor temp.