What is Zone Doubling on a Honeywell VISTA System?

Zone Doubling, available on the Vista-20P, Vista-21iP, and VISTAH3, is a method of using different resistor values to allow compatible single-zone inputs to be treated as two separate zones. In the pairing, the lower number zone uses a 3K resistor. The higher number one uses a 6.2K resistor.

Each of the aforementioned alarm panels have 8 hardwired zones built in. Traditionally, additional hardwired zones are added to the panel using a separate expansion module. But, in some cases, you may only need to add one or two additional zones. In these situations, adding an expansion module is somewhat wasteful. Zone Doubling is perfect for these situations.

On the VISTA-20P and VISTA-21iPLTE only zones 2 through 8 can be doubled, which adds up to seven additional hardwired zones. When zone 2 is doubled, it becomes both 2 and 10, when zone 3 is doubled, it becomes both 3 and 11, and so on. Zone 1 can not be doubled, as it is electrically isolated from all other zones on the panel, and it has a lower resistance tolerance than any other zone (100 ohms tolerance, vs. 300 ohms). This is because it serves as the panel's 2-wire smoke zone.

The VISTAH3 is a little different from the previous panels that support Zone Doubling. Not only can Zone 2 through Zone 8 be doubled, but expansion zones added via the First Alert VISTAHEXPHW can also be doubled. With support for up to 64 wired zones and up to four (4) partitions, the VISTAH3 is the most flexible panel released by Resideo to date. Another slight difference is that when you double a zone on the VISTAH3, the panel automatically assigns the next available expansion zone (Zone 9 or higher) as the second zone in the doubled pair.

The following rules apply to doubled zones:

1. Response Time. The response time programmed for the lower zone number will also apply to the higher zone number.
2. Normally Closed Only. Only Normally Closed devices can be doubled. A short across either resistor of a doubled zone will cause a tamper response (Day/Night) on both doubled zones. When the system is armed, this will report as an E135 and is treated as an alarm. When disarmed, it reports as an E383 and displays as a trouble.
3. Double similar zone types together. Earlier panel versions had issues when dissimilar zones were doubled together, such as when an Entry/Exit zone was doubled with a motion zone. In that particular case, the motion zone will most likely be bypassed in Stay mode, while the Entry/Exit zone will be active. As a result, walking around and faulting the motion zone while in armed stay mode could sometimes cause a false alarm on the Entry/Exit zone. For this reason, it was recommended to only double similar zone types. This was corrected in later versions, but it's not a bad idea to adhere to this logic, even now.
   
   The video below will show you how to wire the 3K resistor to the lower number zone in a zone doubled pair:
   
   
   Honeywell VISTA 21IP: Zone Doubling, Installing Orange, 3K Resisters
   
   
   The videos below will show you how to wire the 6.2K resistor to the higher number zone in a zone doubled pair:
   
   
   Honeywell VISTA 21iP: Zone Doubling, Installing 6.2K Resistors
   
   
   
   
   Honeywell VISTA 21iP: Zone Doubling, 6.2K Resistor Installation (Continued)