Abstract: A water heating device comprising (a) combustion means for igniting a combustible mixture of air and gas for heating water; (b) heat exchanger means for providing heat transfer between the hot gases and the water, the exchanger means including a combustion chamber for receiving the hot gases, a water chamber having an inlet and outlet between which water passes, the water chamber enclosing the combustion chamber, and a plurality of exchange tubes connected to the bottom of the combustion chamber, the tubes extending below the combustion chamber and through the water chamber, such that the hot gases flow through the combustion chamber and then through the tubes in physical isolation from and in heat exchange relation with the water, and the water flows about the tubes and then around the outside of the combustion chamber in counterflow to the hot gases; and (c) temperature control means for controlling the temperature of the water, including thermal measuring means having a sensor for sensing the temperature o

Abstract: A radially fired water heating apparatus (10) having a plurality of stacked segments of multiple-loop, finned coiled tubing (58) separated by inner and outer support baffles (86, 88), all contained within a cylindrical baffle (20) which cooperates with the coiled tubing (58) and support baffles (86, 88) to direct combustion by-products into an annulus (24) promoting heat transfer to a countercurrent flow of inlet air, the water being supplied to and recovered from the stacked segments of coiled tubing (58) through inlet and outlet headers (54, 56) disposed outside cylindrical baffle (20) that can be selectively modified by installing or removing baffles (90, 92) for either single-pass or multiple-pass operation.