Abstract: A system for improving efficiency and effecting fuel conservation in buildings with multiple units heated by forced hot water from a central gas-fired boiler. Each unit or apartment is provided with a circulator pump in the return water pipe and an associated gas valve and meter. When the user in a unit turns on the heat, the circulator pump in that zone is activated to automatically open the associated gas valve which is operated by means of hydraulic pressure differential. The gas from all units flows to a common gas reservoir for discharge to the boiler.