Smoke detector trouble

kurtmccaslin

Active Member
I am getting a false alarm from my fire alarm every time it is a cold morning and the heater kicks on.   
 
My heater is a heat pump that has electric strip heaters which kick when the outdoor temp drops below 30 degrees.
 
My smoke detectors are System Sensor 4WTA-B sensors.
 
The alarm system has been in place for 5 years, with no false alarms.   This year, I have had 3.    
 
This morning I woke up to a fire alarm.   The outside temp was 27 degrees, and there was a very light haze in the house.
 
It seems that there might be a little bit of dust that has accumulated in my heater over the summer, and it burns off when the electric strip heaters come on.   I have experienced this burn-off in the past but it has never triggered an alarm.   
 
I cleaned the smoke detector that alarmed, but could not see any visible dust on it.
 
Has anyone experienced this?   Could the sensor be over-sensitive and need replacing?    Or should I call a HVAC guy to vacuum the dust out of my unit?
 

RAL

Senior Member
I used to have a heat pump with electric back up heat.  Each fall, when the resistance heat would come on for the first time, there would be a slight burning smell, which I attributed to dust on the heating elements.  After the first few cycles. it stopped.  It was never strong enough to trigger the smoke detectors and there never was any visible haze. 
 
It sounds like your smoke detectors are doing their job. I would get the heating system checked out to make sure it is not something more than just dust.  It's possible there is a bad connection in the wiring to the resistance coils, and the poor connection is heating up and burning some insulation on the wires.
 

ano

Senior Member
So these are photoelectric sensors, as is typical for a low-voltage sensor.  They have one light source (LED) and two sensors, one enclosed, the other open.  I would say dust, but sensors have protection against that unless LOTS of dust occurred in a rather short time. ( I have the same sensors.). So maybe dust, or heating strip, but it takes a fair bit of smoke to trigger these. What did you mean when you said you had a "light haze" in your house?  So if you had a "haze" you normally don't, fix that, otherwise, I'd replace the smoke sensor. 
 
I woke up two nights ago when my 120V smoke/CO was beeping. I thought battery but the beeping code was just "malfunction."  So just replaced it.
 

JimS

Active Member
Is your smoke alarm near a heating supply duct?  If so you might want to move it farther away.
 
A slight smell from electric heaters if they haven't been used for a while is normal but it isn't usually enough to make a noticeable haze. 
 
Is this alarm sensor 120V or low voltage connected to an alarm panel?  There are two types of sensors - photoelectric and ionization - and there sensitivity is somewhat different.
 

kurtmccaslin

Active Member
The HVAC tech came in today and found a small leak in the evaporator coil.  When the system pressured up during the heating cycle it was spraying refrigerant and oil in to the ductwork-- fogging the entire house.    The smoke detectors were acting normally and sensed this "smoke" in the house.
 
Thanks everyone for your thoughts.   Problem solved.   
 
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