National Oilheat Research Alliance 21 heating systems assures the highest level of efficiency, safety and fewest service calls. All combustion systems operate best when they are serviced on a regular basis. Good service procedures save fuel and prevent equipment breakdowns. Typical savings from a tune-up are about three percent for systems that are regularly adjusted. If a heating system has not been tuned for several years, or is out of adjustment due to equipment malfunction, then the fuel savings will be higher. Always follow burner-manufacturer recommended burner adjustments to maximize efficiency. Reducing Nozzle Firing Rate Excessive firing rates cause problems for boilers and furnaces. Firing rates that are higher than the heating requirement of the building increase off-cycle loss. Heat loss varies with the off-period time and large firing rates produce long burner-off times. The solution is to reduce the nozzle size, but not below manufacturer recommendations and not below what is necessary to keep the net stack temperature above 350°F. Selecting the correct nozzle size is an important part of proper service procedures. With fixed head burners, it may be necessary to change the combustion head if you are reducing nozzle size. The two exceptions to reducing firing rates are steam boilers and units with tankless coils. In these two cases, the units should be fired to their maximum rating. New units that are properly sized for the load should be fired to the manufacturers’ recommendations. Since most older heating systems are oversized, reducing the firing rate improves efficiency in three ways: • The net stack temperature goes down be- cause the smaller flame produces fewer gases, therefore the gases spend more time in the heat exchanger. This gives the heat exchanger a chance to pull more heat from them. • Off-cycle heat losses are reduced because the burner run-times increase, reducing the time the unit is off. • Cycling losses are reduced. Overfired burners make heat faster than the heating system can absorb it, causing the burner to cycle on and off on the high limit. The burner never reaches steady state. This increases deposits on the heat exchanger and reduces efficiency. An average oil burner only operates about 15% to 20% of the time during the heating season. Heat losses during the off-cycle for older oversized units can be significant. New properly sized boilers and furnaces will not benefit from reducing the firing rate because the off-cycle losses for these units are already very low. The perfect nozzle size is the lowest firing rate that will: • Heat the building adequately on the coldest day of the year • Produce enough domestic hot water • Produce a clean, smoke-free flame with high combustion efficiency • Ensure net stack temperature is adequate Pipe and Duct Insulation Steam pipes, hot water pipes and warm air ducts often waste large amounts of energy when they are not insulated. These losses reduce system efficiency and increase fuel consumption. Duct leak sealing and the use of thermal insulation will prevent unnecessary heat loss. All heating system distribution lines that run through unheated spaces should be adequately protected against heat loss. Boiler Pipes The heat loss from the piping system depends upon several factors: • Temperature of the hot water or steam within the pipes • Length of piping system and the amount of insulation • Temperature of the air surrounding the pipes
NORA Advanced Efficiency
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