diff --git a/homeassistant/components/number/const.py b/homeassistant/components/number/const.py
index 525a99b86c21..99aae56b18cd 100644
--- a/homeassistant/components/number/const.py
+++ b/homeassistant/components/number/const.py
@@ -208,7 +208,7 @@ class NumberDeviceClass(StrEnum):
 
     Unit of measurement: `J`, `kJ`, `MJ`, `GJ`, `mWh`,
     `Wh`, `kWh`, `MWh`, `GWh`, `TWh`, `cal`, `kcal`,
-    `Mcal`, `Gcal`
+    `Mcal`, `Gcal`, `thm`
     """
 
     ENERGY_DISTANCE = "energy_distance"
@@ -231,7 +231,7 @@ class NumberDeviceClass(StrEnum):
 
     Unit of measurement: `J`, `kJ`, `MJ`, `GJ`, `mWh`,
     `Wh`, `kWh`, `MWh`, `GWh`, `TWh`, `cal`, `kcal`,
-    `Mcal`, `Gcal`
+    `Mcal`, `Gcal`, `thm`
     """
 
     FREQUENCY = "frequency"
diff --git a/homeassistant/components/sensor/const.py b/homeassistant/components/sensor/const.py
index 9f396e99d4fc..72d306728742 100644
--- a/homeassistant/components/sensor/const.py
+++ b/homeassistant/components/sensor/const.py
@@ -240,7 +240,7 @@ class SensorDeviceClass(StrEnum):
     electric energy consumption.
     Unit of measurement: `J`, `kJ`, `MJ`, `GJ`, `mWh`,
     `Wh`, `kWh`, `MWh`, `GWh`, `TWh`, `cal`, `kcal`,
-    `Mcal`, `Gcal`
+    `Mcal`, `Gcal`, `thm`
     """
 
     ENERGY_DISTANCE = "energy_distance"
@@ -262,7 +262,7 @@ class SensorDeviceClass(StrEnum):
 
     Unit of measurement: `J`, `kJ`, `MJ`, `GJ`, `mWh`,
     `Wh`, `kWh`, `MWh`, `GWh`, `TWh`, `cal`, `kcal`,
-    `Mcal`, `Gcal`
+    `Mcal`, `Gcal`, `thm`
     """
 
     FREQUENCY = "frequency"
diff --git a/homeassistant/const.py b/homeassistant/const.py
index 6379cc6a5a62..17eae8bcb397 100644
--- a/homeassistant/const.py
+++ b/homeassistant/const.py
@@ -533,6 +533,7 @@ class UnitOfEnergy(StrEnum):
     KILO_CALORIE = "kcal"
     MEGA_CALORIE = "Mcal"
     GIGA_CALORIE = "Gcal"
+    THERM = "thm"
 
 
 # Reactive energy units
diff --git a/homeassistant/generated/sensor.json b/homeassistant/generated/sensor.json
index 836e8b624f5f..8b7327e7b917 100644
--- a/homeassistant/generated/sensor.json
+++ b/homeassistant/generated/sensor.json
@@ -123,6 +123,7 @@
       "MJ",
       "MWh",
       "mWh",
+      "thm",
       "TWh",
       "Wh"
     ],
@@ -145,6 +146,7 @@
       "MJ",
       "MWh",
       "mWh",
+      "thm",
       "TWh",
       "Wh"
     ],
@@ -465,6 +467,7 @@
       "MJ",
       "MWh",
       "mWh",
+      "thm",
       "TWh",
       "Wh"
     ],
@@ -487,6 +490,7 @@
       "MJ",
       "MWh",
       "mWh",
+      "thm",
       "TWh",
       "Wh"
     ],
diff --git a/homeassistant/util/unit_conversion.py b/homeassistant/util/unit_conversion.py
index 13c342860980..e4981acda037 100644
--- a/homeassistant/util/unit_conversion.py
+++ b/homeassistant/util/unit_conversion.py
@@ -72,6 +72,7 @@ _DAYS_TO_SECS = _DAYS_TO_HRS * _HRS_TO_SECS  # 1 day = 24 hours = 86400 seconds
 # Energy conversion constants
 _WH_TO_J = 3600  # 1 Wh = 3600 J
 _WH_TO_CAL = _WH_TO_J / 4.184  # 1 Wh = 860.42065 cal
+_WH_TO_THERM_US = _WH_TO_J / 1.054804e8  # 1 therm (U.S.) = 1.054804e8 J (NIST SP 811)
 
 # Mass conversion constants
 _POUND_TO_G = 453.59237
@@ -414,6 +415,7 @@ class EnergyConverter(BaseUnitConverter):
         UnitOfEnergy.KILO_CALORIE: _WH_TO_CAL,
         UnitOfEnergy.MEGA_CALORIE: _WH_TO_CAL / 1e3,
         UnitOfEnergy.GIGA_CALORIE: _WH_TO_CAL / 1e6,
+        UnitOfEnergy.THERM: _WH_TO_THERM_US * 1e3,
     }
     VALID_UNITS = set(UnitOfEnergy)
 
diff --git a/tests/components/knx/snapshots/test_websocket.ambr b/tests/components/knx/snapshots/test_websocket.ambr
index 07c5794ba60c..f5edfa9f0cf6 100644
--- a/tests/components/knx/snapshots/test_websocket.ambr
+++ b/tests/components/knx/snapshots/test_websocket.ambr
@@ -1940,6 +1940,7 @@
               'psi',
               's',
               'st',
+              'thm',
               'var',
               'varh',
               'yd',
@@ -2318,6 +2319,7 @@
               'psi',
               's',
               'st',
+              'thm',
               'var',
               'varh',
               'yd',
diff --git a/tests/components/template/test_config_flow.py b/tests/components/template/test_config_flow.py
index 5024ad9ec833..5991a94ef8c7 100644
--- a/tests/components/template/test_config_flow.py
+++ b/tests/components/template/test_config_flow.py
@@ -1256,7 +1256,7 @@ EARLY_END_ERROR = "invalid template (TemplateSyntaxError: unexpected 'end of tem
                     "'None' is not a valid unit for device class 'energy'; "
                     "expected one of 'cal', 'Gcal', 'GJ', 'GWh', 'J',"
                     " 'kcal', 'kJ', 'kWh', 'Mcal', 'MJ', 'MWh',"
-                    " 'mWh', 'TWh', 'Wh'"
+                    " 'mWh', 'thm', 'TWh', 'Wh'"
                 ),
             },
         ),
diff --git a/tests/util/test_unit_conversion.py b/tests/util/test_unit_conversion.py
index 09c85a208f95..662b3e72262c 100644
--- a/tests/util/test_unit_conversion.py
+++ b/tests/util/test_unit_conversion.py
@@ -692,6 +692,8 @@ _CONVERTED_VALUE: dict[
         (10, UnitOfEnergy.MEGA_CALORIE, 0.011622222, UnitOfEnergy.MEGA_WATT_HOUR),
         (10, UnitOfEnergy.GIGA_CALORIE, 10000, UnitOfEnergy.MEGA_CALORIE),
         (10, UnitOfEnergy.GIGA_CALORIE, 11.622222, UnitOfEnergy.MEGA_WATT_HOUR),
+        (10, UnitOfEnergy.KILO_WATT_HOUR, 0.3412956, UnitOfEnergy.THERM),
+        (10, UnitOfEnergy.THERM, 293.001111, UnitOfEnergy.KILO_WATT_HOUR),
     ],
     EnergyDistanceConverter: [
         (