Nonsense about oil heat adversely affecting sale of my home in my area. As I have previously explained, I live in a relatively affluent subdivision of early 1970s residences in the MD suburbs of DC. The homes built in 1970-1972 all have gas heat. In 1973 a moratorium was created preventing any new gas hookups and thus the second half of the homes all have oil heat. I do follow property values in our area quite closely and the selling prices have no apparent correlation with heating fuel type. As a retired military service member, I have bought and sold many homes - likely more that most here. Heating method, while an item of immense interest in this forum was not at the top of the list of considerations re any home my wife and I bought. Schools, yes. # BRs and # baths, location, age of home, location, commute, condition, perceived re-sale, all yes. (And likely many other considerations, including working heating. lol) I'm a bit of a TV junkie now that I'm retired. I do watch "House Hunters" and I have NEVER heard a house hunter identify heating fuel as a consideration in their search. There is a lot of bad advice given here due to not "doing the math" - all things being equal, I would prefer to have NG heat rather than oil. Cheaper operating costs, not concern about deliveries, etc. However, I have done the best I can to insulate, reduce heating set point, shift the heating burden to heat pump, and closely monitor costs. I don't have NG available, but based on the costs to bring in NG (based on the experience of a few of my neighbors that were able) it makes absolute no economic sense IN MY CASE. If you don't use very much of an expensive product, your absolute costs may not be that great and the incentive to convert may well be lessened. If you visit the roofing forum, I suspect they'll identify the roof as the most important factor effecting price... in the landscaping forum it will be the grounds, in the kitchen forum, the kitchen and bath. Heating is certainly an important concern, but we need not cry wolf about it.

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.

Your AC company is correct about the return size, although I think you could get away with your present 800 sq in if it were't for the master bedroom issue. While adjusting dampers to provide more airflow to the master might do the trick, you may still need another return in the MBR to get the temperatures evened out. You should have 1000 sq in of filter for a 5ton AC so a 20x20 in the MBR would be more than adequate. A two stage unit would be nice for a couple of reasons: the first stage airflows (supply and return) would likely be inaudible in the MBR and would dehumidify the air better as the run times on first stage tend to be longer. And on those rare occasions you kick into 2nd stage, the 1200 sq in of return with your existing supplies shouldn't be distracting while you sleep. Prices are regional but your estimate doesn't appear too outrageous, especially seeing that they appear to have done their homework on sizing and ducting. A two stage system should add about $1000 on up (depending on the level of system you upgrade to).

"The manufacturers of Vent Hoods are miseducating the consumers." Yes. Somewhat. Not really. They are in business to make money and they do that by making hoods as inexpensively as possible and then selling as many as they can for as much money as they can. Their goal is NOT your health or the IAQ of your home - that is up to you. Telling consumers that they'll also need to spend money on MUA if they buy hood X will negatively impact their sales (ignorant consumer will just go buy a hood from brand Y instead because it doesn't say you need MUA even though it has an identical need for MUA) so they do not want to do that. MUA is also not something that fits well within consumer hood manufacturers world except to the extent that they might offer a hood w/ integrated front curtain ducting. It is much more of a pure HVAC thing. It can be supplied to the return ducts of an HVAC system, the supply ducts or ducted directly to appropriate locations. Incoming air can be heated by gas, electric or hydronic. Incoming air may need to be humidified or dehumidified. It often needs to be electrically integrated with the HVAC system controllers to function properly. Consumer hood manufacturers - ARE NOT IAQ or HVAC people or engineers - they make something decorative that by nature must include air movement so they reluctantly include air movement in their product. Commercial hood manufacturers - ARE IAQ and HVAC people and engineers. Their customers are much more educated than consumers. The one singular purpose of the product they are selling is IAQ - so they design and sell systems that provide good IAQ. Aesthetics is quite secondary for them. Residential HVAC companies in the U.S. - ARE NOT IAQ people (they should be though). A tiny few, less than about 1%, know it well and a few more know it a very little but the vast majority know just enough, based on what they've been told at a 4 hr CEU course, to sound like they know what they're talking about but they don't really understand it. Most residential HVAC people do not understand air movement or why things are done the way they are - they only know how to use tables that tell them to do this or that and as soon as something is outside of defined parameters they're totally lost (though sometimes don't even realize that they're lost). Licensed Professional Engineers do (or most do, some don't) understand air movement and other elements. They are the people who create the tables that HVAC people use. They can think independently. Defined parameters for them are not tables but the physics of air - it's movement, temperature and components. Unfortunately, most U.S. engineers do not have a good understanding of human physiology (except perhaps for biomedical engineers). They do not, for instance, understand how CO2 functions in our bodies and how high levels of CO2 due to poor ventilation affect us. Or how poor ventilation resulting in high levels of VOC's, PM, Carcinogens and Pathogens affect us.