It is even fair to say that if a contact cleaning company spent all day, if the ductwork
was completely exposed and if the ductwork was small enough, a contact cleaning company could technically perform a thorough job if the technician was motivated to perform a thorough job. The contact cleaning method
of air duct cleaning is very limited in what dirt, dust and debris is actually pulled out of a ventilation and or HVAC system. 2” diameter vacuum hoses cannot suck up 3” diameter beer cans or soda pop cans. Due to the laws of physics in that a 2” diameter vacuum hose leaves behind all large diameter items, no airflow improvement is ever realized after the service is performed. Clumsy shop vac hoses usually cannot effectively clean through most furnaces burners, hence the ash, dirt, carbon and dust that can be found in these burners typically stay in the burners. This results in no efficiency improvement when cleaning out the burners, because the shop vac hose could not fit inside of the burners to properly clean it as compressed air or nitrogen can.