Central heating pipe to split into 2 runs
If this piping is for a forced water heating system (a pump moves the water), then either piping diagram will work. If however it is for a parallel connection for pairing 2 or more water heaters and you need the same exact amount of flow to each unit then the right hand diagram is the only choice. In a heating system with a pump, The difference in the length of time for each branch to get hot will not be affected by either piping diagram but by the total length of each run of pipe and the total amount of radiation in each branch. I would recommend that if you are installing a new heating system in a building "zoning" would produce the best results. It would allow each zone or room to be controlled by it's own thermostat.