diff --git a/source/_integrations/modbus.markdown b/source/_integrations/modbus.markdown
index 612c2b45149..417dbd730a9 100644
--- a/source/_integrations/modbus.markdown
+++ b/source/_integrations/modbus.markdown
@@ -756,13 +756,24 @@ climates:
               description: "Value corresponding to Fan Diffuse mode."
               required: false
               type: integer
+    hvac_onoff_coil:
+      description: "Address of On/Off state.
+        Only use this setting if your On/Off state is not handled as a HVAC mode.
+        When zero is read from this coil, the HVAC state is set to Off, otherwise the `hvac_mode_register`
+        dictates the state of the HVAC. If no such coil is defined, it defaults to Auto.
+        When the HVAC mode is set to Off, the value 0 is written to the coil, otherwise the
+        value 1 is written.
+        **Cannot be used with `hvac_onoff_register`.**"
+      required: false
+      type: integer
     hvac_onoff_register:
       description: "Address of On/Off state.
         When the value defined by `hvac_off_value` is read from this register, the HVAC
         state is set to Off. Otherwise, the `hvac_mode_register` dictates the state
         of the HVAC. If no such register is defined, it defaults to Auto.
         When the HVAC mode is set to Off, the value defined by `hvac_off_value` is written to
-        the register, otherwise the value defined by `hvac_on_value` is written."
+        the register, otherwise the value defined by `hvac_on_value` is written.
+        **Cannot be used with `hvac_onoff_coil`.**"
       required: false
       type: integer
     hvac_on_value: