Condensate drains from air conditioner coils, condensing furnaces, and heat-recovery ventilators should not drain directly into a DWV pipe. An indirect drain using an air gap should be installed. In some locations, the direct connection of a condensate drain line into a stack is not permitted, even with a trap. The potential danger is that sewer gases may enter the house through the condensate drain line. It is not a cross-connection problem, but it is unsafe and unhealthy. www.nachi.org & www.apollohome.com