Today a furnace that is rated 80% efficient can vent exhaust gases up a chimney (like most current installations). After May of 2013 the federal government has mandated that all new furnaces installed in homes in Minnesota must be 90% efficient or higher.
These new high efficiency furnaces must use a venting system made of PVC pipe and vent out the side of your home, not the chimney that is used in many current furnace installations. In many homes this will require installing a new vent system. The additional cost of installing the new vent system to accommodate the new higher efficiency furnace will vary from home to home. In multi-family housing and town homes installing the new venting system can be challenging and add significant costs. You could be looking at additional hundreds or thousands of dollars in carpentry work to facilitate the high efficiency furnace venting.
If your furnace will need replacement soon you should learn the impact of the costs of installing a new PVC pipe venting system will have on your furnace replacement project. We are onboard with saving energy and being green, however in some instances it may be hard to justify the longer payback time due to the added venting work. Until the new mandate goes in to effect you are free to install a less efficient furnace and use your existing chimney vent.