High-Tech Maine Heat Pump Maker Fails, but Questions Remain ~ The power is on, but no one’s home at 110 Hildreth Street in Bangor, Maine, the commercial warehouse building that until recently housed the plant and offices of cold-climate heat pump pioneer Hallowell International. In 2007 and 2008, Hallowell was the darling of the energy-efficiency buzz machine, announcing with supreme confidence the introduction of an advanced two-stage heat pump that would heat homes in northern climates with three times the efficiency of ordinary electric heat. Even in zero-degree weather, these heat pumps were supposed to be cheaper than oil heat —