fan. Use your manometer to test the air pressure difference again between the combustion air zone and outdoors. Open or close interior doors to create worst-case depressurization (the highest negative draft possible) in the combustion air zone. Once You Have Created Worst Case Fire the water heater if it is a separate unit and test to be sure it is operating properly. Then fire the boiler or furnace and check the draft overfire and in the flue for all the combustion appliances for back drafting and spillage. Also check for CO ambient and in the undiluted combustion gases. The results you are looking for are: -.02" wc (-5 Pascals) overfire draft, less than 35 ppm CO ambient, zero to trace smoke. If any appliance fails the spillage or draft test under worst case, repeat the test under normal conditions. If it still fails, determine the reason and fix the problem. Fixes for Depressurization If the building’s air leaks are sealed and 44 National Oilheat Research Alliance the fans are preventing sufficient air for the burner’s combustion, outdoor air must be provided. This can be accomplished with a fan in a can, an air boot on the burner or an air box on the burner. The return air ducts should also be checked for leaks in the CAZ. If there are leaks, the furnace blower (the largest fan in the house) is pulling air out of the CAZ and sending it up into the building. The blower on the furnace is depressurizing the burner on the furnace! The following are fixes for depressurization of the CAZ: • Seal leaking ducts (especially leaking returns in the combustion air zone). • Add point source ventilation for problem devices. • Isolate combustion for burner. • Install carbon monoxide detectors on every floor. • Advise the customer to only run one big fan at a time and not to run fans if there is a fire in the fireplace or woodstove. Figure 2 Worst Case Test
NORA Advanced Efficiency
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