Is the Alarm.com Smart Thermostat compatible with dual fuel and hybrid HVAC systems?
Yes. This document provides an overview, wiring diagrams, and setup instructions for dual fuel and hybrid HVAC systems in order to provide support for Alarm.com Smart Thermostat (Smart Thermostat HD, ADC-T2000, and ADC-T3000) installations.
Overview
Homes have a dual fuel HVAC system when there are two separate HVAC units that provide heat, with one usually being a heat pump, or one complete system providing heat only and one complete separate system providing cool only.
The most common types of dual fuel systems are:
- Gas furnace with a heat pump
- Boiler with a heat pump
Other Hybrid HVAC Systems include:
- Electric Furnace with a heat pump – technically considered just a heat pump but behaves like a dual fuel.
- Boiler with a cooling system only
Most thermostats, including the Alarm.com Smart Thermostat, can handle the two independent systems by separating the circuits that connect to power terminals RC and RH.
What are RH and RC?
The RH and RC terminals provide power to the thermostat. The RH terminal receives power from the heating source and the RC terminal receives power from the cooling source. If there is only one power source, then the RH and RC terminals are connected through the external jumper on the ADC-T2000 or internal jumpers on the ADC-T3000.
The ADC-T40K-HD can only be powered when the RH and C are connected. Connecting RC and C will not power up the thermostat. If there is no C wire available, a different thermostat will need to be used.
Important: For thermostats to use a constant 24V power source, the C terminal must be wired to provide this constant power. When the thermostat utilizes both RH and RC, the C terminal pulls power from the RH terminal only.
It is necessary to set the thermostat up for a dual fuel system, as failure to do so could result in damaging the equipment and/or thermostat. On the ADC-T3000, this is done by manually selecting RC and RH on the wiring setup wizard on the thermostat. On the ADC-T2000, the jumper must be removed to ensure the circuits are independent.
When the thermostat is configured to use RC and RH, or the jumper is removed, different function wires connect to different power sources. The table below shows which terminals connect to which R power terminal:
| RC | RH |
|---|---|
| Y | C ** |
| Y2 | W |
| O/B (for ADC-T2000) O & B (for ADC-T3000 and ADC-T40K-HD) |
W2 |
| G | Z (for ADC-T2000) Z1 (for ADC-T3000 and ADC-T40K-HD) |
| Z2 (for ADC-T3000 and ADC-T40K-HD) | - |
**Important: It is important to note that the C terminal connects to the RH system. Trying to connect the C wire to the RC system may cause damage to the units and/or thermostat.
Wiring diagrams and setup instructions
The following sections cover wiring and installing the Smart Thermostat HD, ADC-T2000, and ADC-T3000 thermostats on dual fuel systems.
Important: An HVAC professional should be contacted for any questions regarding wiring.
ADC-T2000 and ADC-T3000 installation
Notes:
** C wire is required for operation of the ADC-T40K-HD. This wire is optional for the ADC-T2000 & ADC-T3000, and will allow the thermostat to act as a Z-Wave repeater but must be connected to the Rh circuit.
** O can be replaced by B, and vice versa, in the diagram depending on the heat pump type.
** ADC-T3000 installation bypass should not be necessary since the thermostat should automatically detect system type and wiring based on wire detection.
Gas Furnace with Heat Pump
Wiring diagram and thermostat setup.
ADC-T40K-HD Setup
| Heat Type | Fossil |
|---|---|
| HVAC Type | Heat Pump |
| Pump Stages | 1 for Y only 2 for Y and Y2 |
| Aux Stages | 1 for W only 2 for W and W2 |
ADC-T3000 Bypass Setup
| RC/RH Selection | RH Only |
|---|---|
| System Type | Pump |
| Aux Stages | 1 for W only 2 for W and W2 |
| Pump Stages | 1 for Y only 2 for Y and Y2 |
| Backup Heat | Fossil |
ADC-T2000 Manual Configuration
| DUAL | For heat pump systems that energize the reversing valve on a call for Cool (O oriented) |
|---|---|
| DULB | For heat pump systems that energize the reversing valve on a call for Heat (B oriented) |
Operation
| Normal Call for Heat | Y and G (and O/B depending on the heat pump type) will energize turning on the outdoor condenser and the indoor fan. |
|---|---|
| Auxiliary Heat |
Y and G turn off and W energizes turning on the gas furnace. Important: The gas furnace must not run at the same time as the heat pump. |
| Normal Call for Cool | Y and G (and O/B depending on the heat pump type) will energize turning on the outdoor condenser and the indoor fan. |
Heat Pump with Boiler Auxiliary - Three wires between boiler and thermostat (1)
Depending on the boiler system, desired thermostat functionality, and available thermostat wires, not all thermostat may be compatible.
Contact an HVAC professional with any questions or concerns.
Wiring diagram and thermostat setup.
ADC-T40K-HD Setup
| Heat Type |
Fossil will run the boiler independently when auxiliary heat energizes. Electric will run the boiler in addition to the heat pump when auxiliary heat energizes. |
|---|---|
| HVAC Type | Heat Pump |
| Aux Stages | 1 for W only 2 for W and W2 |
| Pump Stages | 1 for Y only 2 for Y and Y2 |
ADC-T3000 Bypass Setup
| RC/RH Selection | RH and RC |
|---|---|
| System Type | Pump |
| Aux Stages | 1 for W only 2 for W and W2 |
| Pump Stages | 1 for Y only 2 for Y and Y2 |
| Backup Heat |
Fossil will run the boiler independently when auxiliary heat energizes. Electric will run the boiler in addition to the heat pump when auxiliary heat energizes. |
ADC-T2000 Manual Configuration
| DUAL |
For heat pump systems that energize the reversing valve on a call for Cool. (O oriented) Run the boiler independently when auxiliary heat is called. |
|---|---|
| DULB |
For heat pump systems that energize the reversing valve on a call for Heat. (B oriented) Run the boiler independently when auxiliary heat is called. |
| PUMP |
For heat pump systems that energize the reversing valve on a call for Cool. (O oriented) Run the boiler in addition to the heat pump when auxiliary heat is called. |
| PMPB |
For heat pump systems that energize the reversing valve on a call for Heat. (B oriented) Run the boiler in addition to the heat pump when auxiliary heat is called. |
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Operation:
| Normal Call for Heat | Y and G (and O/B depending on the heat pump type) will energize from the RC terminal turning on the outdoor condenser and the indoor fan. |
|---|---|
| Auxiliary Heat |
If the Backup Heat Type (ADC-T3000), Heat Type (ADC-T40-HD), is set to Fossil or System Type (ADC-T2000) is set to DUAL or DULB:
If the Backup Heat Type (ADC-T3000), Heat Type (ADC-T40K-HD), is set to Electric or System Type (ADC-T2000) is set to PUMP or PMPB (ADC-T2000):
|
| Normal Call for Cool | Y and G (and O/B depending on the heat pump type) will energize turning on the outdoor condenser and the indoor fan. |
Electric Furnace with Heat Pump
Wiring diagram and thermostat setup.
ADC-T40K-HD Setup
| Heat Type | Electric |
|---|---|
| System Type | Pump |
| Aux Stages | 1 for W only 2 for W and W2 |
| Pump Stages | 1 for Y only 2 for Y and Y2 |
ADC-T3000 Bypass Setup
| RC/RH Selection | RH Only |
|---|---|
| System Type | Pump |
| Aux Stages | 1 for W only 2 for W and W2 |
| Pump Stages | 1 for Y only 2 for Y and Y2 |
| Backup Heat | Electric |
ADC-T2000 Manual Configuration
| PUMP | For heat pump systems that energize the reversing valve on a call for Cool. (O oriented) |
|---|---|
| PMPB | For heat pump systems that energize the reversing valve on a call for Heat. (B oriented) |
Operation
| Normal Call for Heat | Y and G (and O/B depending on the heat pump type) will energize turning on the outdoor condenser and the indoor fan. |
|---|---|
| Auxiliary Heat | Y and G stay on and W energizes turning on the electric strips in the furnace. |
| Normal Call for Cool | Y and G (and O/B depending on the heat pump type) will energize turning on the outdoor condenser and the indoor fan. |
Boiler with Air Conditioning Only
Wiring diagram and thermostat setup.
ADC-T40K-HD Setup
| Heat Type | Fossil |
|---|---|
| System Type | Normal |
| Aux Stages | 1 for W only 2 for W and W2 |
| Pump Stages | 1 for Y only 2 for Y and Y2 |
ADC-T3000 Bypass Setup
| RC/RH Selection | RH and RC |
|---|---|
| System Type | Normal |
| Aux Stages | 1 for W only 2 for W and W2 |
| Pump Stages | 1 for Y only 2 for Y and Y2 |
| Backup Heat | Fossil |
ADC-T2000 Manual Configuration
| System Type | FOSL |
|---|
Operation
| Normal Call for Heat | W will energize from the RH terminal, turning on the boiler. |
|---|---|
| Normal Call for Cool | Y and G will energize from the RC terminal, turning on the air handler and condenser. |