It used to only fill up in the summer with the air conditioner running.
furnaces to take moisture out of the air also. I live in MN and in the summer we run a dehumidifier and in the winter we don't because of the furnace taking out the extra moisture
Is this a newer furnace? If so , is it a high efficient furnace? If it is it will have plastic venting and the water is due to the condensate produced from the low temperature flue gases. When gas burns one of the by products is water, ussually this makes it up and out the chimney when the flue gas is hot. On high efficient furnaces they absorb so much of the heat the flue gas temperature is much lower, and starts to drop the moisture out of the flue gas. Your venting is designed to slope back to the furnace and drain the water back to the drain. If the flow tube is overflowing then there is probably a problem with the drain line being plugged. At that point the heat exchanger can fill with water and the preasure switch for the venting will not work and the furnace will not run anymore. Water comming out is normal, water backing up into the furnace is not.
