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NORA Advanced Efficiency

doors to the supplied rooms are closed the air pressure will rise, and warm air will be forced out of any air leaks in the room. The pressure in the room with the return register will be less than atmospheric pressure and dry cold air will be sucked into this room. Water condenses on cooler surfaces. If those surfaces are inside the wall and ceiling cavities it can cause serious problems. In the summer, less than 60% humidity is comfortable; in the winter, humidity should be less than 40% to avoid condensation. Living in a home creates a great deal of water vapor; if the home is so dry it needs a humidifier, it probably has spectacular air leaks that should be fixed instead. Water Solutions Stop water from leaking into the building. Make the walls and roof watertight, fix plumbing leaks, keep water away from the building (gutters and grading), seal dirt crawl space and basement floors, install a sump pump to eliminate standing water, be sure exhaust fans are vented to the outdoors, and install or improve air/vapor barriers. Ventilate with dry outdoor air to dilute more humid indoor air, and improve insulation to keep indoor surfaces warmer, resisting condensation. If the basement is wet, get rid of the water before sealing up the air leaks. Determining the Heat Loss for the Building Understanding Building Science helps understand heat loss. When replacing a boiler or furnace, always do a heat loss calculation for the building! Most units in the field are oversized. Many buildings have had home performance work done that decreases losses allowing for a smaller boiler or furnace. 38 National Oilheat Research Alliance Why Oversizing is bad: larger units cost more than smaller ones, the bigger the unit the greater the off-cycle losses, the heat input outruns the heat output, therefore the burner short cycles and never reaches steady state. This lowers efficiency by one to three percent as soot and scale deposits on the heat exchanger increase. The best way to calculate heat loss is with heat loss software. To do a proper heat loss, a floor plan of the building and building construction information is needed, including: wall construction materials and insulation, window and door details, floor, ceiling, attic and basement details, and the building owner’s desired indoor temperature (the Indoor Design Temperature). Steps to Determine Heat Loss • Determine the design temperature difference. • Obtain dimensions of all heat loss surfaces, (any surface with heated space on one side and unheated space on the other). • Determine Transmission Heat Loss Factors. • Determine Infiltration Heat Loss Factors. DTD—Design Temperature Difference The DTD is the Indoor Design Temperature minus the Outdoor Design Temperature for


NORA Advanced Efficiency
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