I recently had a high energy furnace installed with PVC pipe for the air intake and heat exhaust. The PVC sticks out of the side of the house and the guy who installed the furnace said not to put any screening over the pipe because in very cold weather (northern Illinois) condensation could collect on the screen, freeze and seal off the inlet or outlet. I am afraid that the three inch pipe is going to look like a highway to heaven for squirrels and other varmints that want to get into the house. I can see how regular window screen might freeze up but I wonder if I could seal those holes with 1/2" hardware cloth or even chicken wire. It doesn't seem that holes that large would freeze up. Any info is appreciated. Thanks.