Based upon Brookhaven National Laboratory testing, jacket losses from appliances can vary from less than 1% to more than 10%. This loss is highest while the burner is firing. Typical flame temperatures of approximately 2,000°F drive heat through the chamber wall and then through the jacket. Furnaces and dry base boilers that do not have water surrounding the combustion area tend to have higher jacket losses than wet base boilers in which the water backed heat exchanger extends around the combustion area to the floor. One way to capture some of the jacket losses from a boiler or furnace installed in a basement is to seal up the air leaks into the basement and insulate the basement walls down to a level below the frost line. This results in the jacket losses heating the basement and the basement ceiling (the floor of the first floor). Distribution System Losses, Pipe and Duct Heat Loss The heat from a central boiler or furnace is transported to the home through pipes or air ducts. Heat loss that occurs between the heating unit and the living space causes system inefficiency, Figure 5. The level of loss depends upon how and where the pipes or ducts are installed, the size of the distribution system and the amount of thermal insulation. Uninsulated pipes and ducts that run through unheated areas have large heat losses. A properly designed and installed heat distribution system Figure 5 Pipe and Duct Loss 14 National Oilheat Research Alliance can operate with very low duct or pipe losses. Heat losses from steam or water pipes and air ducts are not measured in appliance efficiency ratings by the government (AFUE-Annual Fuel Utilization Efficiency). They do not appear in the AFUE rating and vary widely from building to building. Outdoor Air Infiltration All fuel-burning heating units consume air for combustion and for off-cycle draft. The air that passes out of the house through the chimney must be replaced by cold outdoor air drawn into the home. When the cold air is brought into the house, it goes through the living space and is heated. The energy required to heat this cold air is the infiltration loss. In most cases, a burner operating in an unconfined space of a conventional building will receive adequate combustion air supply from air leaks into the building. But if the burner is located in a confined space, such as a furnace or boiler room, the enclosure must have one permanent opening into the rest of the building near the top and one near the bottom of the enclosure to let in combustion and draft relief air. If the burner is located in a tightly constructed or properly sealed building, outside air should be supplied for combustion. The size of air infiltration heat loss depends upon on-cycle airflow through the heating unit,
NORA Advanced Efficiency
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