Electrical – wiring hrv in a confusing house

some beautiful pictures

first time posting apologies if my placement is off

Buying HRV.
I am debating between two units, venmar evo5-700 which doesn’t support furnace interlock or lifebreath rnc205, which does support furnace interlock. Based on my duct setup (simplistic) I would likely need interlock. I am in Canada and during winter the house gets humid during winter, tons of frost on windows.

Ill will include as many pictures as I can, including a visio drawing.

The setup has a fresh air intake, others have indicated there is likely an electronic controlled damper, however I know on the fresh air intake there is only a manual damper, it is currently visible near the furnace and I do not recall a damper along the duct while I was drywalling the basement.

Upstairs we have an ecobee (pictured) which controls furnace, ac and humidifier. And a ventilation switch which controls the furnace fan and the bathroom fan.

Downstairs, I have traced most the wires, the vent switch goes to a junction box labeled “MUF” which goes to a transformer and then a relay (G7L-2A-BUBJ-CB) and then to a switch (RIBX24SBA) near the panel which is set to closed, which means on, I tested with multimeter. This switch controls a 14/2 wire which I now know goes to the hood range fan plug in the kitchen. Which makes no sense because you wouldn’t be able to turn on the range fan without the vent switch on.

As well there is a junction box labeled “cold switch” this has power from the panel to the furnace, as well a another 14/2 wire which is wired backwards (black on white from power and black on black to furnace), no idea where this wire goes or if its relevant.

Finally, there is the random 3 wire low voltage wire dangling that I assume comes from the same wall as the ecobee, I have not confirmed this but based on ducts and location It would be possible to rout new wires to basement from ecobee/vent switch wall.

I know this is a lot of information, essentially, I just want to install an HRV unit and want to wire it the best way possible. Ideally it would be controlled through the ecobee but I gather I can not control a second device (on top of my humidistat). I know you can get digital control panels for hrv’s, which again I could setup on the same wall, though it would be nice to replace the current vent switch, the problem being it is running 14/2 wire so I would need to get a receptacle switch which may not have all the programable features, maybe a timer. It would be nice to wire it to turn on whenever the furnace turns on, then I could set the ecobee to run the fan every hour or so, not sure if you are supposed to do that. Though I think most set the HRV’s dynamically, so they push out moisture in winter and don’t run them in the summer except for fresh air intake. In my case I know I would need it running lots in winter.

TL/DR; ambitious person in lockdown procrastinating on schoolwork by installing an HRV, confident in duct work but no idea how I should wire the thing.