Upon arrival the technician found that the primary drain line is installed incorrectly allowing the condensate to drip onto the gas line. The water is running down the gas line towards the return air filter chase and leaking onto the decking / ceiling. Extensive water damage is present. I recommended to the homeowner that they replace the rusted secondary drain pan, re route the drain lines outside of the house and install an in-line float switch to prevent this from happening again in the future.