Chilling is produced from heat that is normally wasted in the economizer section of a steam boiler. A thermally-activated ammonia-water absorption chiller is powered by a heat recovery unit. The heat recovery unit supplies boiler exhaust heat to desorb the working fluid of the chiller. That can be directly, such that the heat recovery unit is a heat recovery vapor generator that can be colocated with an economizer, in parallel or series. The exhaust heat can alternatively be supplied to the AARC indirectly, via a heat transfer loop and a separate generator. The desorbed ammonia vapor is rectified, condensed, and then used to produce the chilling. The heat released in the chiller when low pressure ammonia vapor is re-absorbed is used to preheat the boiler feedwater.