My house was constructed in the mid-'80s with a mid-efficiency furnace with a B-vent, and no provision for a/c.

I'd really like to do whatever I can to make upgrading less expensive, either for my own future use, or resale.

I can run a lineset out there through a fairly snug chase that runs right out to the side of the house, exactly where I'd want to put the a/c compressor, it's ideal.

I don't know the sizing exactly, and I suppose I could get someone in to figure it out, but as I understand it, an oversized line set would not be an issue.

My plan would be to run/do everything I can so it's ready to go, including concrete pad, cable, line set and perhaps even the vent/air intake pipes, which leads me to my question:

From what I've seen on new construction I've worked on, some people run oversized pipes and reducers. I'm figuring on just running the pipe into the mechanical room, and a future installer would connect them to the new furnace.

I know cement type's really crucial for condensing furnaces- you have to use the right cement for the right brand of pipe, so I'm wondering if it's going to be an issue two or three years later? If I buy brand x pipe, will there be an issue if the installer wants to use their own brand of pipe/cement?

And, can I go oversized, rather than risk being undersized? I thought I'd terminate them outside if possible, so the exterior is finished and ready - either with the combined vent/intake type, or the 90 degree offset sweep elbows I've seen used (I'm in BC Canada.)