I have a new TRANE 19 SEER furnace installed October of 2006. We have installed a radiant barrier on the underside of the OSB/shingle roof in November 2007. We added white formaldehyde free insulation without paper backing to the attic to replace the 30 year old degraded pink stuff. We hired our trusted HVAC person to reroute some ductwork in the attic and repair a large hole in the cold air return in November, 2007. We expected to see some changes in the attic and house temperatures. We did not expect to see the temperature in the attic at 70 degrees when the outside temperature was 20 degrees less. We put a large thermometer in the attic to test and a backup small one to make sure the first one was working. We began to suspect a leak in the ductwork somewhere. I found a large gap at the furnace where the outcoming heated air is not going into the Selkirk galvanized pipe which vents through the roof. The round pipe is not connected fully and I can almost insert my hand into the angled opening. After reading your explanation of the Acidic Moisture and CO, I am wondering if you could comment on whether or not I should cover and duct tape the opening until the TRANE person who has helped us through the purchase and installation of at least half a dozen furnaces and air conditioners over a 20 year time span can get to it after January 1. I have not called him yet. His repair people were here to train us in how to clean the filter that removes almost 99% of particulates. (Even if it does not remove that many, it has improved my indoor air quality so much, that I am happy with it.) I think that the service persons may have accidentally caused the disconnection. My main concerns are determining the safety of this situation and if the attic that is now the temperature of the house and not the outside is another problem we must address.

I think my vent is 4", I have a Bryant Plus-80 furnace, and I just replaced my hw heater, (I'm in BC Canada so YMMV) - the flue hat for the hw heater is sized for the vent that's there, I hadn't thought of that aspect - if I replace my furnace with a HE one - since I just shelled out on the new hw I wouldn't want to change it just yet (but I guess I would run the plumbing for a he hw heater when I do the furnace- Both furnace and hw heater Y into a single vent of course, if it was hw only, would there be a reducer that runs off the flue hat? I could certainly see a difference if it was only one appliance using the vent, but I've never seen any condensation coming back down....I wonder if OP's issue might also be some negative pressure....which could be dangerous. jmnoelle13, can you try a test for us? Get a stubby candle like a tealight, and place it right next to the flue hat on top of your hw heater, when the heater's at work, and see if the flame of the candle is drawn towards the flue hat? If it is, all is well in terms of airflow, if not, your system or parts of the ventilation system in your house is drawing combustion products back down the vent, which is very dangerous. Your new furnace should have two side vents, one for exhaust, one for combustion air. You probably didn't have direct combustion air feed before, so you should be better off in that regard. As for reducing the vent size, can you drop a sleeve down inside the vent from above?

Before you do anything, try pulling the connection apart. Many times the installer does a dry fit of the PVC and then forgets to glue them together. If you get lucky you may be able to prime and glue it together to stop the leak. The connection would have to be completely dry to do this. That will mean shutting down the furnace to allow everything to dry. I don't know of any trick other than carefully planning and cutting. You can do a dry fit of everything before gluing. In most cases the PVC pipe has some give to it. It helps when replacing a section.

Austin, should be there a filter somewhere else in the air handler? If you look under the air handler it is probably open, you would be looking straight at the AC coil by looking up under the unit. You could put a filter in the filter rack of the unit in that slot under the pvc drain line that comes out lower right of the AH. Also, what are the ramifications of this poor setup? The evaporator gets dirty, which can freeze the coil or clog the condensate drain and water leak down all over the water heater and onto the floor. Potential IAQ problems as it's harder to keep coil clean. Excessive cleaning can lead to refrigerant leaks if not performed properly. Pain in the butt to work on, due to no room. Leads to corner cutting which in turn leads to further problems down road. Will I still get cool air with the AC turned down? Sure it will cool fine, as long as their are no outstanding problems. It can work, it is just not how I would install a system, because you are just begging for problems and having to deal with higher maintenance costs with this kind of set up. With that said, there may be no other better place to put it. Sometimes to cure something, you have to tear it down and start over.