Fireplaces, Heating Stoves, Flues and Chimneys - Cumbustion air inlet Vs. Cold air inlet?

Whats the difference? My fireplace instructions state the cold air inlet is for Canada only and I'm in the U.S. but I'm curious. The descriptions make them sound as if they do the same thing. On my fireplace the coldair inlet is on top and the combustion air inlet is on the right side. The coldair inlet on top is covered by a metal plate but does not seem like its seeled. If I am not going to be using this cold air inlet do I need to seal that closed?

Fireplaces need air to burn properly. If your home is "tight" you may have a problem with using the fireplace. Many fireplaces have an inlet for outside air to enter so it is not trying to suck air from inside the house to burn properly. On some older installations, there was no provision made for outside air and the owners had to open a window a bit to be able to have a fire going.