My high-efficiency gas furnace uses two PVC pipes to connect with the outside world. One (I think the exhaust) has a drain for water that condenses in the pipe; the other (the air intake, I think) has no drain. I know that there's moisture in the pipe because there's a drip where the nearly horizontal pipe enters an elbow to drop vertically to the furnace. During the winter, it drips at the rate of about 4 fl. oz. per day. Should I install a drain similar to the one that's on the other pipe ?
the exhast on your furnace must have the drain because the heat creates moisture in the pipe which should run back down hill towards your furnace, then through the furnace to a drain or pump to the outside, the other pipe is the intake, which give your furnace the air it needs to keep your gas flame burning, [no air no flame] this pipe should not have water in it, the outside termination should 90 down so there is no way for water to get inside.so if there is water in the intake pipe of the furnace you could have a problem