I have a furnace with an uncovered air intake. I cant imagine it is pulling very much fresh air in through the duct because it is uncovered. I am wondering, is this correct? I believe there should be some grill covering this. Should I cover the outside panel so that most air is being pulled through the duct?
Outside:
Intake:
Duct work:
Overview:
Best Answer
It's hard to tell from your photos, but I believe that duct is a passive makeup air system.
When the furnace goes on it needs to exhaust gasses out the flue. For it to be able to exhaust gasses it needs to recover fresh air.
Most buildings have plenty of little leaks which can let air get back in. But some new homes are built with sealed building envelopes, trying to keep the home bottled up. This presents a problem for gas burning appliances (or any exhaust appliance for that matter).
Ducting in from the roof will allow the furnace to recover air, but it's unlikely to seriously impact your thermal envelope.
If your home were "too air tight" then your furnace wouldn't work.