diff --git a/esphome/automation.py b/esphome/automation.py
index 32f423d2a34..42731118c94 100644
--- a/esphome/automation.py
+++ b/esphome/automation.py
@@ -338,8 +338,9 @@ class ApplyField:
     Double a literal brace in a template. ``conf_key`` may be a path into nested sections.
     ``type_`` may be a C++ type string using ``{parent}`` when the type is only known per
     instance. ``const_fn(config, value)`` renders a constant's argument text when ``cg.safe_exp``
-    is not the right spelling (unit conversion belongs in the validator); a lambda or an id
-    bypasses it, so the target must also take a plain ``type_``. An absent key emits nothing.
+    is not the right spelling, or the value depends on another entity's config, such as the unit
+    a climate reports in; a lambda or an id bypasses it, so the target must also take a plain
+    ``type_``. An absent key emits nothing.
     """
 
     conf_key: str | tuple[str, ...]
diff --git a/esphome/components/climate/__init__.py b/esphome/components/climate/__init__.py
index 10c901d63dc..c195c86bd12 100644
--- a/esphome/components/climate/__init__.py
+++ b/esphome/components/climate/__init__.py
@@ -167,10 +167,8 @@ def temperature_unit_of(config: ConfigType) -> str:
 
 def temperature_unit_of_id(climate_id: ID) -> str:
     """The unit of the climate with this id, for actions that take static temperatures."""
-    for conf in CORE.config.get(DOMAIN, []):
-        if conf[CONF_ID] == climate_id:
-            return temperature_unit_of(conf)
-    raise KeyError(f"No climate with id {climate_id}")
+    path = CORE.config.get_path_for_id(climate_id)[:-1]
+    return temperature_unit_of(CORE.config.get_config_for_path(path))
 
 
 def temperature_in_entity_unit(
diff --git a/esphome/components/water_heater/__init__.py b/esphome/components/water_heater/__init__.py
index a54bb35b6c4..028648d7bcf 100644
--- a/esphome/components/water_heater/__init__.py
+++ b/esphome/components/water_heater/__init__.py
@@ -54,10 +54,8 @@ def temperature_unit_of(config: ConfigType) -> str:
 
 def temperature_unit_of_id(water_heater_id: ID) -> str:
     """The unit of the water heater with this id, for actions that take static temperatures."""
-    for conf in CORE.config.get(DOMAIN, []):
-        if conf[CONF_ID] == water_heater_id:
-            return temperature_unit_of(conf)
-    raise KeyError(f"No water heater with id {water_heater_id}")
+    path = CORE.config.get_path_for_id(water_heater_id)[:-1]
+    return temperature_unit_of(CORE.config.get_config_for_path(path))
 
 
 def _visual_temperatures_in_entity_unit(config: ConfigType) -> ConfigType: