Low Flue gas temperature causing condensation

[sanrishi]

hearthman:
You can forgive my ignorance.

Carnak:
As you advised, I have checked the system setting in tstat. It was set to 6. I have changed it to 3. Now, the fire stays on for longer(actually it stayed for 6 minutes as opposed to 3 minutes when the system setting was set to 6). But, I still collected some water in the attic overnight( less amount of water than it used to be). Can I just leave the setting at 3? Would longer run of fire harm the furnace in any ways?

Thank you.

[Carnak]

Furnaces are designed to run constant.

The thermostat suggestion was for short cycling and has nothing to do with the condensation.

You have been advised to have your furnace clocked and set to the proper firing rate.

You have also been advised that it is possible that your B-vent chimney is too large of a diameter and that you should have a 4-inch double walled vent connector from the furnace to the chimney.

Can't do anything more for you online. Call the gas authority there whether it is the gas company or a city inspector.