i'm about to pick a contractor for my new modcon gas boiler, and to this point, not one suggested relocating the boiler to the outside wall where the new gas line will come in, as opposed to where the old oil boiler was. if the new boiler is installed where the old unit was, we'd have to run the pvc piping about 40 feet to the only outside wall where the exhaust and intake can be placed. it just seems to be easier, but copper pipe for 3 heat zones will have to be relocated along with the boiler, which is more costly than pvc. or we could use pex to bring the old lines to the new boiler, which won't be as expensive. afterall, what reason do we need to be near the original spot if we're not using the old chimney?