any reasonable compost heap of large enough size , would provide heat for about 4-6 weeks . So piping would need to be removed and relaid in that same time scale.That would be lots of fiddly work , I did it and it really is a fiddle.
Thats why the brush compost heap works better, because it takes so much longer to break down and the shear size helps keep it working too. Thats why I thought a tank the size of a hot water tank, would be better for a smaller muck heap . The main heat would be in the middle, where the tank would be put !! A heavy duty galvanised tank would last much longer than an old copper tank or maybe even longer than black plastic. Unless the plastic pipe is special heat proof stuff , it's life span would be quite short.
The tank method is much easier to maintain too , remove old compost without fear of puncturing plastic pipe etc . If using horse manure and straw , the heap will heat up almost immediately and could be turned on a weekly basis to maintain maximum heat . This could be done for 4 weeks or so , or until heat dropped too much . Which ever way you go it means heavy work , on a regular basis.
If a fork lift was available ? a system of pallets could be made with wire cages (about the size of IBC wotsits) fitted, and then filled with horse manure and straw , then placed around the heavy duty water tank , like spokes round a hub !!. some form of lid put on the centre and then the whole lot would heat up . As heat dropped in the containers , they could either be taken away by fork lift, and remixed or replaced with fresh . This would then be a perpetual system , with easy change over. Water tank would be semi permanent , as would fittings . This system would last a long time and would be quite easy to make using second hand materials . Thats how I thought of doing it anyway ... drawback ...no fork lift !!!!

cheers
Russ