I am assisting a friend on some basic maintenance on their furnace. I noticed they have a duct from the outside that is attached directly to the return air plenum. I assume it was supposed to put fresh air into the house. I have seen this before but with a heat exchange on a super insulated house. This is not a super insulated house and no heat exchanger is used. Would we be better off to remove this source of outside air to the return air plenum?