Concentric vents make it easier to have a two-pipe installation for high
efficiency furnaces. These vents simplify installation and only require one hole
through the wall or roof where the pipes terminate. Without using these vents,
the installation would require cutting two holes through the home, one for each
pipe. These vents save time and money by reducing the amount of work
required. Available in 2in, 3in or 4in intake vent sizes.