Attic fans can suck air down flues causing spillage. Spillage can cause CO poisoning. Attic fans can't always be easily accessed or controlled. Read on:
While doing a comprehensive quality control visit last week, our Pure Energy Final Inspector noted that both the atmospheric draft water heater and atmospheric draft boiler failed these safety tests:
In addition to failing those tests, the negative pressure in the combustion appliance zone (CAZ) with reference to the outdoors was greater than allowed (the CAZ exceeded the maximum CAZ depressurization limit allowed) during the baseline and under the worst case conditions set up.
Upon further investigation, the Final Inspector found that, not only were the typical mechanical ventilation appliances making the CAZ negative, but the attic fan was on as well.
The attic was being ventilated to the outdoors by a typical attic fan installed in the roof. The pressure caused by the operating fan is sucking air out of the attic... and the house, and the CAZ, causing the CAZ to be under too great a negative pressure. Since every CFM of air that the fan exhausts has to come from somewhere, this negative pressure causes some of the make-up air to come down the flues rather than from the passive attic vents. The water heater and the boiler could not vent the flue gasses properly, and the fumes actually were being vented to the inside of the house. This is dangerous and unhealthy.
The reason the fan could suck air from the CAZ is because the attic was not fully separated from the house and from the basement as is required by the program and also from BPI.
So, not only does a leaky pressure boundary allow heated air to leak into the attic; moist air to leak into the attic; hot summer air to leak into the house; polluted air to leak into the house... but it also can impact the CAZ and cause CO and other pollutant poisoning.
Recommendations for program administrators and technicians: