A DOE rule requiring all indoor gas furnaces to be at least 90% efficient will be delayed pending a court challenge. While the idea behind the rule of driving higher efficiency seems desirable, there are some buildings that simply cannot use a 90% furnace due to venting or other considerations. An example of impossibility would be replacing an 80% efficient furnace in an unheated attic. Since 90% furnaces make condensate (water), and condensate freezes, this type of application is just a disaster waiting to happen, and should not be mandated.
The HVAC industry is hopeful that if and when the final rule is rolled out, there will be provision for exceptions due to impossibility of performance or excessive cost hardships. A little common sense, industry knowledge, and providing flexibility to on-the-ground code officials to adapt to unanticipated situations will go a long way to resolving the problems while substantially accomplishing the objective.