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Honeywell Equipment Interface Module is one way to wire multiple thermostats to control a single zone or device - cited & dicussed at Inspectapedia.com How to Wire Multiple Thermostats Together
"Parallel" Thermostat Wiring to Control One Cooling or Heating Zone

How can we use multiple temperature sensors or thermostats to control a single heating or cooling zone in a building? You may not be able to wire two thermostats exactly in parallel, but using multiple wall thermostats or temperature sensors to control one individual heating or cooling zone is easier than you might think.

This article series explains how to control heating and cooling controls in buildings.

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Parallel or Multiple Room Thermostat Wiring Instructions

Thermostat wiring reference chart - simplest case two-wire thermostat (C) Daniel FriedmanHow to wire multiple remote temperature sensors to control a single zone valve, circulator, heater, or air conditioner

Using widely-available Honeywell remote indoor temperature sensors and a Honeywell room thermostat that is designed to accept remote-control from wired thermostats we can control any individual heating or cooling zone from one, two, or even up to nine different locations. Here we describe the wiring details for that easy solution.

Alternative methods for using multiple temperature sensors to control a single heating or cooling zone, such as by wireless thermostats is discussed separately.

On 2021-03-27 by Patrick - I need to wire 2 simple hydronic heat only T-Stats in parallel

I need to wire 2 simple hydronic heat only T-Stats in parallel to independently activate a single Honeywell V8043 F 1036 Valve. Any chance I can get a wiring diagram to complete this. I understand the implications regarding the 2 T-Stats not working in synch but that is not an issue.

On 2021-03-27 by (mod)

@Patrick,

Thank you for a helpful question that I'd re-state as:

How can I wire a single heating zone valve to be operated by either of two separate room thermostats (in different rooms) or by both if both call for heat simultaneously.

I offer several answers here.

Best solution: Combine Remote Temperature Sensors with a Special Thermostat

[illustrated above] Use 1 (or you may need two) Honeywell C7189U Remote Indoor Sensors along with a Honeywell VisionPRO 8000 with RedLINK technology, Programmable, 1H/1C, Touchscreen Thermostat.

Depending on the remote sensor model and thermostat model you choose, you may need to use two remote sensors (one can be in the same room as the thermostat) because in at least some installations when remote sensors are used the thermostat's own internal room temperature sensor is out of operation.

Wiring instructions are in this

HONEYWELL C7189U REMOTE INDOOR SENSOR INSTALLATION MANUAL [PDF] Honeywell International Inc., 1985 Douglas Drive North, Golden Valley, MN 55422 USA Website: yourhome.honeywell.com

This a wired device. There are also wireless thermostat alternatives that can operate a zone valve, circulator relay, (boiler - hot water heat) or a forced air system (warm air furnace heat)

Watch out: Honeywell explains:

How to connect or wire multiple remote temperature sensors to a single heating or cooling zone thermostat or device -adapted from Honeywell, cited & discussed at Inspectapedia.comOnce a remote indoor temperature sensor is connected to the thermostat, the thermostat's sensor is no longer used. The thermostat's installer setup should be modified to tell the thermostat that remote indoor temperature sensor(s) have been used. The Inside temperature reading on the thermostat's display will be the remote sensor(s) temperature location(s).

That's why I said you may need to use two remote temperature sensors along with the contolling thermostat itself.

Also download this example

HONEYWELL VisionPRO® Series with RedLINK™ INSTALlATION GUIDE [PDF]

This approach permits use of multiple remote temperature sensors (from 1 to 9), any of which can turn on the heat - in your case by operating the zone valve.

It avoids the problem with improper thermostat current draw and possible heat anticipator malfunction that could occur if we simply wired-up two older style room thermostats in parallel.

The wiring diagram below shows correct wiring when using multiple Honeywell C7189 remote temperature sensors with a VisionPro RedLINK Thermostat.

The installation instructions show that the sensors are wired in series through to the thermostat S1 and S2 terminals.

Up to 9 sensors, wired in parallel sets of three at a time, can be connected to the base thermostat.

Watch out: Be sure to review the specific thermostat and remote sensor features and wiring instructions before buying and having these devices installed.

Possible solution: some thermostats may be wired in parallel

Depending on the thermostat models chosen, this approach may not be as safe: simply wire up two room thermostats in parallel, either or both of which can turn on the heat by operating the zone valve. Many modern electronic thermostats do not include a traditional resistor-type heat anticipator.

Watch out: if these thermostats use a conventional heat anticipator it may not work properly when two thermostats are wired in parallel on the same circuit and when both are calling for heat.

More about heat anticipators is at HEAT ANTICIPATOR OPERATION


Possible solution when need to control both cooling & heating

Use a separate Equipment Interface Module.

For readers who need to control both heating and cooling equipment from multiple rooms or locations, take a look at the Honeywell Equipment Interface Module (EIM) that can work with all Prestige IAQ and new RedLINK VisionPRO Thermostats.

See this HONEYWELL EQUIPMENT INTERFACE MODULE INSTALLATION GUIDE [PDF]



References for Wiring Multiple Thermostats or Sensors to Control One HVAC Zone

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THERMOSTAT WIRING in PARALLEL / MULTIPLES at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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INDEX to RELATED ARTICLES: ARTICLE INDEX to HVAC THERMOSTATS

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