Ive just installed a Goodman furnace model# GMH950704CXAA I'm having excessive moisture coming from the heat exchanger, the furnace is around 13yrs old but never hooked up or turned on before. It's a three burner system all are working well . There are two drain hoses the water is draining from the exchanger side however there is a lot of moisture in combustion vent pvc before I hooked it up I inspected the heat exchanger there didn't appear to be any holes or rust.my question is could water build up be because of a problem with the way I vented the system or could there be another problem.