When a cylinder system apparatus is to be heated by two boilers, one boiler is generally connected to the cylinder in the usual way, and the pipes from the second boiler connected to the pipes of the first one, flow to flow and return to return. No fault can be found with this arrangement, which works well, whether either boiler is used separately or both are used together, and no stopcocks are needed. However, a better arrangement is to connect the pipes from each boiler into the cylinder independently, instead of allowing the pipes to join outside the cylinder. In this case there is the possibility of more uniform results, and it seems a more correct way to do the work, although no fault can be found with the plan first explained.