We must clean all of the vents attached to your system. If we did not clean all the vents, dust and debris from the uncleaned vents would continue to circulate through your home and your heating system, finding its way back to your newly cleaned furnace and quickly diminishing the benefits of having the system cleaned at all. The ductwork for an individual is all connected so doing a partial cleaning of the system would not be fair to you as a customer. We also fully guarantee our work, which is something that we could not do if we only cleaned part of the system.