CO (Carbon Monoxide) is from incomplete combustion, This is caused by not enough oxygen atoms. When carbon burns it wants to join with two oxygen atoms. This menage-a-tois is natural. If you starve the burning of oxygen you will get CO; actually you will get a mixture of carbon monoxide and carbon dioxide as some carbons find two oxygens and come carbons find only one.
Your description of an air leaky construction leads me to believe that there is more than enough oxygen for complete burning. Plants will also not be harmed by a little CO.
If you really want to be safe, nuy a CO detector and let it check for you.
They're "into it."