Today I've discovered multiple issues with the gas furnace. And some issues I discovered with his plumbing leading to the tankless water heater. Worn out inducer motor Out of tolerance flame sensor Out of tolerance ignitor Out of tolerance gas valve. Build up on the return grill Ripped duct work Pull and clean blower motor and reinsulate furnace System is 15 years old and at this point needs to be rebuilt to insure reliability. System number 2 is the exact same and I recommend we rebuild it.