An easily repairable, high efficiency, durable, compact heat exchanger having a modular heat exchanger tube may be provided. The modular heat exchanger tube may be easily disassembled so that any of its modular component tubes (such as its combustion area tube) may be easily removed for repair or replacement. Internal alignment and sealing sleeves may be provided for the adjacent modular component tubes of the heat exchanger tube. The internal sleeves may automatically and permanently increase their sealing power due the automatic and permanent expansion they undergo when they are stress relieved by being heated for the first time by the combustion gasses within the heat exchanger tube. Stress cracking of the heat exchanger tube may be reduced by supporting the heat exchanger tube so that it may move freely as it heats up (expands) and cools down (contracts) during the normal thermal operating cycles of the heat exchanger. The energy efficiency of the blower for the heat exchanger may be increased by providing a low resistance air path within the heat exchanger. A passive, secondary ignition point device located downstream from the flame bullet within the heat exchanger may increase the thoroughness of the combustion of the fuel within the heat exchanger tube, thereby increasing the amount of energy extracted from the fuel, while simultaneously reducing the amount of pollutants produced by the combustion of the fuel. The heat exchanger's compactness may be increased by using a folded or formed heat exchanger tube which may not utilize any heat exchange fins.
