Thank you for the help Bob. After opening and checking all the intake vents, I found that someone, in their supreme intelligence, had partially bent a steel sheet that acts as a barrier from the outside air into the intake duct. They did this to pass some wiring. Once that was re-sealed, no cold draft and the house stays warm.

For the life of me, I don't understand why jumper grills got so popular. While I know why they are there, no heating person here in TX can explain that if the furnace is in the attic and the central return is in a common area, the filter is on the furnace, then why cut and install another box in the common area versus just run the duct back to return plenum at the filter? I think it was left over from central filter return grilles in the common area that was the only means of filtration but never readjusted their install techniques. I was somewhat pleased in my new home after running the bedroom returns to the plenum; (which worked better and balanced system out). I used two of the three in the common area for a ducted central dehumidifier and the 3rd for an additional ceiling return to complement my existing low wall return.

I eventually had my HVAC guy come out and asked him. He said it was okay to partially block the heat vent, but if it had been the cold air return it would NOT have been okay. So I happily moved the frig to it's best place and moved the frig right up against it. So the heat vent is about halfway blocked and I just put one of those magnetic vent covers over the half behind the frig. I'm not an expert, but I think it helps to force more air out of the half that's not blocked. So, unlike most kitchen renovations, this cost me nothing. Yay!

You'll hear a lot of debate about this one - some will say you can't do it without calculating a Manual J etc but the reality is there's a lot of boilerplate hvac systems, at least where I am in Canada. I have two returns in the upper floor of my house only a couple of metres apart, and none in the finished basement and none in any of the bedrooms, which I've been told is an 'impossibility' - well here in Canada, it's not and the system works well enough - the master bedroom is a bit cooler with the door closed, but it's above a poorly insulated garage. I see a lot of basements with the return in the ceiling. Warm air does rise, though, and in the summer you might want some of that cooler air in the basement circulating upstairs, so I'm planning to do exactly what you mentioned, put the return near the floor, backing onto the furnace room. If there was some sort of big issue with changed airflow, you could probably block off an equivalent of the downstairs return vent in the upper return, to equalise the air flow, but to this layperson, the SUPPLY of cold air is not as much of an issue if you're not getting cavitation (a vacuum effect because the pump isn't able to suck in as much air as it's trying to deliver.) Take some temperature readings over a few hours in different spots in the house, and make note whether the furnace is running a lot more than it was previously. The 'duct work' typically is either the space between floor joists or a boxed duct around the same size, or, running down the wall, typical stud wall spacing, 16." That's what I see here in British Columbia, again, I'm not an HVAC tech. Don't go excessively large. If you go through the furnace room wall you won't need much in the way of ducting and if you need to you can use thermopan (silver faced cardboard) instead of drywall or OSB to form the 'duct' from the floor up to the return (make sure you cut into the return, not the warm air section and make triple sure you're not going to damage any wires, gas lines, a/c lines etc. As for the return, the standard size grille is about the width of the space between studs I guess so around 16?" If you need to tweak it, you can block sections of it or the upstairs one inside under the grille if you need to. If you're careful, you're not going to damage anything irrevocably.