I live in a Cape. From what I can tell the second floor was finished (and heat added) after the first floor had been built.
In the pic above, to the left you see my knee wall (finished bedrooms on the other side)... On the right side of the pic you see the pipes fed up from the basement--they pass directly thru a closet on the first floor, they literally drilled holes in the floor and ceiling of the closet and passed the bare pipes thru exposed and sitting out about 1" from the finished closet wall just inside the door.
It may be tough to see, but at the base of the knee wall you can see that of the two pipes that came up from the floor, one pipe goes away from the camera, and the other comes toward it, those are the feed and return from two bedrooms that make up my second floor. There is a third pipe beneath those that interconnects the baseboards in the two sets of baseboards. The baseboards have their return looped underneath the fins, so both pipes exit the knee walls in the same space.
Two of these pipes run directly in front of the access hatch to this space, so you have to awkwardly climb over them to enter this attic space.
The pipes are 3/4".
My heating bills last winter were insane, over $500/mo @ $3.10/G for heating oil, and that was when the house was vacant and heat set at 55-60*. This year oil is 10-20% more expensive, so I've got to do something. I have some insulation contractors in and they have said the same thing: You need to relocate those pipes, otherwise the best we can is box them in with rigid foam and it won't be pretty and won't be very efficient either.
Truth be told I'm looking for a reason to relocate them anyway because I hate that the bare pipes are exposed in that first floor closet. They are susceptible to damage in there, and they can also burn you. I'm willing to tear apart the walls/ceiling in there to relocate them into the wall cavities. The plaster skim coat is completely ruined in there anyway, either from a roof leak (or maybe from a leak from these pipes that has since been fixed? who knows...)
What are my options for relocating these pipes?
I have 2x8 joists -- could I drill two 15/16ths holes to pass 3/4" PEX through? I was thinking that is that is possible I could setup the baseboards to drop their feed/return into the joist cavity on the inside of the knee wall, bore my holes and run all pipes on the "inside" of the joist cavity, which will then have an air block installed and insulated on the other side. I currently have full access to the joist cavities for boring and running the PEX, the first floor closet runs parallel to the joists, so I'd be able to pick a wall and then open up a stud cavity to run the pipes through.
If I can't drill thru the joists then I was thinking another option might be to build out the lowest 6" of my knee walls with 2x6's, then I could safely bore through those to run the PEX. At the access hatch I'd raise the lower lip by 6" to accommodate the boxing, so it would now be more like going thru a window vs. going thru a tiny door.
Another couple of Q's--
The crusty looking valves in the pic above--are those air bleeders? Why are they necessary if this is just a giant loop of pipe? Why can't the lines be flushed at the boiler?
I have two heating zones each with it's own pump--the second floor is the one we've been talking about. The first floor uses a big loop of cast iron pipe with "mono flow tees" leading to convectors. I know those need to bled if the system is open and that it's a huge PITA. Would I need to bleed the first floor as a result of opening up the pipes on the second floor?
BTW, here's a pic of the first floor units--these are NOT the ones I'm re-piping--but I just wanted you to know what the first floor was in case those had to be bled as well: