Upon diagnosis turned heat on and allowed unit to go thru it’s cycle, I performed combustion analysis on unit due to tenant claiming her smoke alarms go off, unit ignited and cycle thru, no high level of CO were found while unit was running. Mac of 8 PPM on stack, furthermore I attached K-type thermo-couple on supply plenum and measure a supply temp inside plenum at 125 degrees. This is a good supply temp.
Now what we did notice was that customer stated she had some ice maker/Humidifier work done, current Humidifier is a Skuttle bypass style old model 190, this bypass side of Humidifier is fully open to the utility room where a water heater is present and furnace, meaning this 6” opening to the return side of the furnace is drawing all this air into the furnace including possible the exhaust gases from water heater when it runs causing the smoke alarms to go off, unit can not run this way as it’s grabbing return air from within the utility room(picture was taken)
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