Furnace Ideas / Help

Too bad you didn't find this out sooner. It just might be an issue, depending on how the internals and condensate drain is made. Some of these use an (typically) external PVC trap system to keep the combustion gasses (under slight pressure) from exiting through the drain system and into the heated space (house). If this is a "big ol" barn a little bit of gas leakage might not hurt. You MAY be able to modify the drain so that the condensate can all escape along with a little bit of combustion gas, which might not hurt in a large ventilated area

Going to need a link to the furnace documentation/ install/ service literature and some photos of the installation and drain/ vent hookups