The direct vent blowers pull air and vent gases from the heater to the outdoors. They require 115 volts to run the fan inside, a relay in the unit is used to control the burner.
They can be ordered from your local plumbing/heating supplier. Many plumbers are experienced with the installation. Considering that it requires heater experience as well as venting installation and electrical knowledge it is not a do-it-yourself project.