First of all, warmer air always tends to rise, and colder air tens to descend. So inside a room you will find warmer air near the ceiling and colder air near the floor. (anyway, the difference is not huge - maybe 5 °C ). My opinion is that your furnace will never suck the air from the upper half of your living room, yet it may suck the air from the lower half - or may not - depending on how well your windows and doors are insulated. I shall explain that briefly.
As shown in the diagram, your furnace is by no means a vacuum pump; every bit of air that rises is immediately replace by an equal amount of air. This mass of replacement air can come either from above (from the flue) or from front (from the ventilation holes in the furnace's door)
Situation 1: your house is hermetically insulated - all your windows and doors are perfectly air proof (this rarely happens in practice)
This means that the replacement air from the furnace's door will have to be sucked from the basement, which in turn will suck it from the rest of the house, meaning that some amount of air will leave the house without being replaced, thus your furnace would work like a vacuum pump. BUT PHYSICS DON'T WORK THIS WAY!!! Because the air pressure inside the house will tend to be equal to the air pressure outside the house, all the replacement air will be sucked from above, via the flue. So, in this situation, NO AIR CIRCULATION inside the house.
Situation 2: your windows and door are not perfectly air proof
Still, the largest amount of replacement air will be taken from the above, via the flue, but some air will be also taken from the furnace's door vents. This air will be sucked from the basement, which will suck it from the rest of the house, which will suck it from the outside of the house, via your non-hermetic windows and doors. But, the air flow WILL ALWAYS FOLLOW THE SHORTEST PATH POSSIBLE. As shown in the picture, you will get some air circulation, but only in the lower half of your room. This means that the air in the lowest half of the room will get replaced by outside air, which is colder; the upper half of the room will not get disturbed, but since air masses will exchange heat until thermal equilibrium, this means that OVERALL, YOU WILL END UP LOOSING SOME HEAT.
The problem could be the high humidity in the house. Here, north of Pittsburgh, Pa. I run a dehumidifier any time I am using the A/C unit to help reduce the humidity. Most A/C units are oversized not allowing the unit to run long enough to reduce the humidity. If you live in a high humidity area the A/C unit will not remove enough of the humidity in your house to allow you to feel comfortable. I set my dehumidifier at 40% and allow it to run automatically. I bought a GE unit rated at 70 pints per day from Sam's club and it keeps the humidity in check. One more thing, the drip line should have it's own trap close to the unit to keep cold air from blowing down the pipe causing the pipe to become cold which in turn coupled with a high humidity in the house causes it to swet. I would probably allow the condensate drain to run outside the house if that is legal in your area.
Best Answer
HELL NO
Whichever joker is installing an 80% furnace with a PVC pipe for the exhaust needs their license revoked pronto, because that's a patent CO hazard. Non-condensing appliances operate at flue temperatures well above the safe working temperatures of PVC or any other plastic, and thus need to be vented using a metal B-vent. (Conversely, condensing appliances generate corrosive condensate that will eat ordinary B-vent alive. Stainless steel double-wall can be used as a "universal vent", and is what you're supposed to use on condensing appliances as per UL listings, but the condensing gas appliance manufacturers haven't quite gotten the memo incorporated into their install manuals yet.)