An economizer uses the heat in hot exhaust (combustion) gases to preheat the feedwater before it enters the boiler. This recovered heat boosts overall plant efficiency by reducing the energy the boiler must supply to turn water into steam, and it also lowers fuel consumption and thermal stress on the boiler. Heating feedwater with steam would require a separate steam-driven feedwater heater, not an economizer. Combustion air is heated in an air preheater, not in the economizer. The role of the economizer is specifically to transfer heat from the exhaust gases to the feedwater.

Open feedwater heaters rely on heated water to preheat the feedwater before it enters the boiler. If the water coming from the heater is too hot, its vapor pressure is high enough that, once the water is drawn into the feedwater pump, any pressure drop on the suction side can cause some of the water to flash into steam. That steam forms a pocket in the pump suction, filling it with vapor and preventing the pump from lifting liquid — a condition known as steambound. When the pump is steambound, it loses prime and can’t deliver the required feedwater to the boiler, risking boiler operation. Note that higher temperature does not reduce cavitation risk; it typically increases it because vapor pressure is higher. Also, while overheating protection may trip, the immediate pump-related effect of water being too hot is steambound, not an improvement in efficiency.

The essential idea is that a safety valve relieves pressure by opening to vent steam. It is designed to lift at a set pressure so that steam can escape and prevent the boiler from going over its maximum allowable working pressure. The immediate action you observe is the valve popping open, releasing steam, and then reseating once pressure drops. It isn't meant to regulate temperature or to increase pressure, and while it prevents reaching the MAWP, the specific, observable function is to pop open.

Proper venting provides the path for both bringing in the right amount of air and removing combustion exhaust safely. When venting is correct, the system draws balanced air for efficient, complete combustion and channels away hot gases and potential pollutants. This balance helps maximize fuel use, reduce wasted fuel, and prevent dangerous backdrafts or the buildup of CO inside the space. If venting is inadequate, exhaust can reflux into the building, combustion can become incomplete, and harmful gases can accumulate, threatening safety and efficiency. Water leaks, on the other hand, aren’t caused by venting, and venting doesn’t control electrical supply, so those points don’t apply.

Heavy fuel oils are very viscous, especially in cold conditions. The heaviest grade contains more waxy content and higher molecular weight, so at room temperature it can be thick enough to resist being pushed through pumps, lines, and filters. Heating is used to lower that viscosity so the fuel can flow smoothly and be delivered to the burner with reliable atomization. If it isn’t heated, the pump can struggle, filters can clog, and combustion may become unstable. Lighter fuel oils flow much more readily at normal temperatures, so they typically don’t require heating just to pump. Heating them is not usually necessary unless the temperature is so low that they begin to thicken, which is less common for these grades. So, the essential idea is that the heaviest grade must be heated before pumping to ensure it can be pumped, filtered, and atomized properly for reliable boiler operation.