PIRs for house with ceiling heating & cooling vents and "pets"!

[eddy <eddyweddy@xxxxxxxxx>]

I recently had an alarm system installed, consisting of a NX-16 panel,
magnetic reeds on all doors and DSC encore PIRs in the main living
areas. The PIRs, according to the installer are immune to small pets.
In my case the pets consist of one 12kg Cavalier King charles spaniel
who spends all his time sleeping and a 8kg, 15 year old cat who sleeps
even more! Then there are the 2 Roomba discovery automatic vacuum
cleaners, dinner plate size gadgets who run around the house at
regular intervals sucking up debris.

However, it was not this collection of pets who appear to have caused
the problem. I also have heating and cooling ducts in the ceiling
because the house is all on one level and built on a concrete slab. At
the moment, because it's still early spring here, the heating
occasionally comes on at 6.30pm. Because I sometimes get home only
after 7.30pm, the heating has been running for around an hour. Over
the last 8 weeks, practically every PIR in the house has falsed at
least once after 6.30pm. Some of the heating ducts are within 3 ft of
the PIR.

To be absolutely sure, I have actually "banished" the pets from the
house, but the false alarms still continue.

To make matters worse, even if I did disable the timers that operate
the thermostat, my heating unit is a ceiling mounted model which has a
fan controller that is triggered by the ambient temperature inside the
unit. In days that are hot enough, the heat in the roof is actually
high enough to trick the fans into coming on, which in turns causes
warm air to circulate into the house. And this has caused at least one
false alarm ...

In a situation like mine, are there PIRs which are capable of handling
the disturbance from the heating ducts, or is the only option to have
the PIRs removed from the security system ?

rgds, Ed