If you live in the Colorado Springs, Colorado area, you are probably 6,000 to 9,000 feet above sea level. The air is much thinner up here and that has a profound, detrimental effect on the performance (cleaning ability) of all vacuum cleaners.
We have found through actual testing in our customers' homes and our own home, that even the most powerful single-motor vacuum will leave two-thirds of the dirt in the carpet. Let me say that another way. The most powerful single-motor, that draws about 13.5 Amps of current at 120 volts, will only remove one third of the dirt from a carpet at this altitude.
Our testing has shown that to remove the heavy sand and grit from a carpet, requires a central vacuum with two motors that produce about 1,000 air watts at a 1 and 1/8 inch opening (that's the inside diameter of the wands).
If you have low pile, commercial carpet like you see in hotels, then you may be OK with a single-motor. If you have moderately thick, cut-pile carpet then my belief is that you must have a twin-motor with around 1,000 air watts if you want to remove the damaging sand and grit from your carpet.