We are looking at installing the connection wiring and pipes between the exterior and interior boxes, under the slab. This is due to distance and going in any other diretion, such as up the wall into the roof space, then down, due to it being a double height space, would exceed the maximum distance the piping can go. Has anyone else done this? We have been told by one installer to make sure the builder puts in a 100mm PVC pipe under the slab between the units, and they will then be able to push the pipework through. However another installer appears to suggest wrapping the pipework up and installing it into the actual concrete slab before they pour it. I think option B sounds a bit risky, as any movement of the slab from earthquakes etc, could damage the pipe. Also It isn't future proof, so if something goes wrong with the heatpump and it needs replacing, you can't easily install new pipework. Whereas a PVC conduit pipe allows you to pull new pipework through in the future. Anyone have any suggestions? Would the heatpump pipework between the exterior and interior units, be able to work with a new heatpump in the future if it even needs replacing, or would they need new pipework? I have found installer have given such conflicting information, even on the actual sizes that the heat pumps based on the room volumes need to be!