They are not as powerfull as regular vacuums. All that extra piping and air leaks add up.This house has a "whole house vacuum" which just quit.
We broke out the old vacuum cleaner and vacuumed the den. Holy shit. The container on the vac was full of dirt/lint/dust before the whole room was vacuumed. And 1/2 again by the time it was done.
I've come to the conclusion whole house vacs do not suck enough.