The landscape in the heating industry, with regard to residential and commercial boiler rooms, has drastically changed. Over the years, when you entered a typical boiler room in the Northeast, it was very common to find a sectional cast iron boiler or boilers and usually some type of indirect heating appliance for domestic hot water. It could be a side-arm heat exchanger with a storage tank or a storage tank with the heating coil installed directly inside. Nowadays, it has become quite common to find high efficiency modulating and condensing gas-fired boilers (either LP or natural). These boilers are not your average "run of the mill" atmospheric gas boilers either, because their efficiencies range between 90% and 96%. They use a Neg/Reg gas valve and fan assembly, which means the amount of gas that flows into the burner for combustion is regulated by the fan assembly's blower speed. The blower speed is controlled by an onboard micro-processor that is performing several internal calculations to determine the appropriate amount of British thermal units (BTUs) needed to satisfy the call. Hence the modulating part... it only uses the amount of gas necessary to satisfy whatever load it is currently "seeing."
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