This palm-sized combustion unit weighs less than 0.2 kg (5 oz.) and can provide heat for portable personal heating/cooling devices, indoor heating systems such as baseboard heaters, in-line water heaters, and fuel cell systems. An array of modules can heat a house efficiently and reduce energy losses by 45 percent. It's the first device of its kind and offers unique opportunities for miniaturizing heating and heat pump devices. MicroHeater achieves its small size, affordability, and very low levels of emissions by relying on high rates of heat and energy mass transfer though specially fabricated microchannels carrying hot water.