Cindy, Below is a paragraph from page 10 for the installation manual for the Carrier 59MN7 modulating furnace. I think you will find something similar for other furnace brands. "When the furnace is installed as a direct vent (2-pipe) furnace, no special provisions for air for combustion are required. However, other gas appliances installed in the space with the furnace may require outside air for combustion. Follow the guidelines below to insure that other gas appliances have sufficient air for combustion." All furnaces need combustion air to work properly. New homes are built very tightly so it is important to have enough oxygen so the fuel burns completely. If the furnace and other gas appliances are operating at the same time it could cause a dangerous situation. If it were my house I would want the PVC air intake to be installed so it has access to outside air. In my opinion this is an improper installation caused by laziness by the installer. It may be fine, but why take a chance with your parent's home? As you stated they paid a lot of money for this furnace and basement. There is no reason it should not have been done properly. Here is a link that might be useful: Carrier furnace installation manual

It really depends on the situation and every home and need are different. In the basement overcooling situation, you gotta do it for the comfort. Some people have insulation between the basement and living space so you don't want to lose your heating to that area. Then there is the problem with imbalanced pressures. If there are supply duct openings, where is the air going to go? If the basement is closely coupled to the area with a return (upstairs?) and you don't mind a little air down there to dehumidify, or warm it up a little bit, leave it alone. If the basement is sealed off from the return upstairs, it may leave the area more closely coupled to the outdoors. It will be pressurized and the air will tend to leak out through the openings and cracks to nature. That will, in turn, depressurize the living space and suck unconditioned air from random cracks and openings up there. It might even come down some flues. If that is going on, you gotta fix it. You can do it by adding a return or sealing the supplies. Ducting systems are complicated. I hate them.

Update: Today the building owner brought in a air-duct cleaning person to take a look and prepare an estimate. I didn't make a great first impression. I didn't know it was the owner. When they came in, I made a face and said I thought we were going to do testing first and that I wanted new ducts rather than duct cleaning that makes a mess. The owner retorted "i've been doing this for 50 years...I have many buildings. I know what I'm doing...". Jeez. Building owner does not make an HVAC expert. And not updating a 30-year old system and letting the building get to this state doesn't speak to his landlord credentials! Although, I do commend the responsivness and willingness to fix the problem. I tried to make nice when I figured out who he was. I had told my boss earlier air-duct cleaning was the last thing I wanted after stories I read about it making a mess of the office, but I guess he didn't mention it to the owner as I requested. So the 4 of us (owner, boss, me, airduct rep) had in depth conversation about the issues. The airduct cleaning guy said it is very rare to find mold in this type of scenario but they do look for it and will clean it if it is minor or stop and report it otherwise. When I told him I had read multiple stories about office air-duct cleaning leaving a mess behind, he replied that those companies failed at their job. He assured us there is no mess or disturbance left behind. He described the process in detail, but I zoned out in the tech talk. I didn't hear that they cover or clean all surfaces. They claim the technique cannot generate extra dirt. hmmppph. We talked about air-quality testing (which he does not do), and they were unclear if it would serve a purpose. To me, test then treat seems to be the natural order. One would want to know the particulate count b4 and after cleaning, right? I surely do. It is still up in the air what we will do. My boss said maybe he will pay for the testing if the owner won't. He seemed to agree with me that testing first was the right thing to do, but yet he still seems inclined to use dust on surfaces as a metric. I said its the stuff you can't see that the testing is for. Is it? I don't really know. Meanwhile, I bought an air purifier for my bedroom. Its on order. I can't wait to see if I wake up less congested. Meanwhile, the heater hasn't kicked on much or maybe at all this week. I stopped taking my inhaler last week to see if coughing came back this week. The temps have picked up a bit and we get a lot of afternoon solar heating. I almost wanted to put the A/C on today it was so warm. So it might be difficult to assess anything once heating season dies down.

I'll tell you ray HVAC wasn't my trade of choice, it wasn't even in the top 30 list, it just happened and I couldn't wait to move on. Personally I think the trade sucked with no sense of achievement and just became basic hard work, so I moved into other trades, but again learned they also became basic unrewarding jobs with only a pay check. No more rewarding than hauling hay or standing on an assembly line to me so I moved on. Do you really think I spent my life at Baylor doing that job? I've never worked at one place longer than 4 years in my life with exception to the last 20 before retirement and it wasn't a trade. My real passion started in 1975 when I enrolled into the university of Kentucky to major in chemical and electrical engineering so I could help develop sustainable alternative sources of energy inspired by the oil embargo of 73-74. The goal ended when I discovered my level of intelligence was par, but I had a problem with retention and attention. I moved to Texas and enrolled into a HVAC technician program which at the time was where many college rejects and laid off blue color workers went at the time. After years of learning and working in many trades I realized I never felt satisfied with any and was only pulling a cart. I was smart enough to not want to pull a cart but knew I wanted to ride the cart. Riding the cart would give me the freedom to follow my passion so I made drastic changes in my life and moved again. What I did for the last 20 years before retiring put me on the cart but I'm still not satisfied. I'm still obsessed with my passion from 1975 and still working on sustainable alternative energy and the answer is everywhere (another topic). I'm glad you receive satisfaction from what you do ray, but to be frank you do not impress me, and to be fair I am nothing to be impressed by either. People who are impressive contributed more to humanity than one who learned the basic principles of refrigeration and installing air conditioners. People will never remember what you say but always remember how you made them feel, so good or bad you may remember this. Get off your narcissist highchair old man and realize when you retire all you have is time to the day you die. It's worthless if nothing is done with the time and if you die a rich old man it's a disgrace if both were wasted without giving back. Your opinion is worthless, there are 7 billion in the world to choose from so back off on the all mighty Ray rants on how valuable your opinion and time is. I service AMERICA in all the trades, so what!