diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 83d3ee3..3ebb745 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -2,6 +2,95 @@
 Changelog
 =========
 
+Version 7.4.0 (UNRELEASED)
+==========================
+
+Breaking Changes
+----------------
+- **Temperature Setpoint Limits**: Replaced hardcoded temperature limits with device-provided values
+
+  - ``set_dhw_temperature()`` now validates against device-specific ``dhw_temperature_min`` and ``dhw_temperature_max`` instead of hardcoded 95-150°F bounds
+  - ``build_reservation_entry()`` changed parameter name from ``temperature_f`` to ``temperature`` (unit-agnostic)
+  - Added optional ``temperature_min`` and ``temperature_max`` parameters to ``build_reservation_entry()`` for device-specific limit overrides
+  - Temperature parameters now accept values in the user's preferred unit (Celsius or Fahrenheit) based on global unit system context
+  - Fixes Home Assistant and other integrations that prefer Celsius unit display
+
+  **Migration guide:**
+
+  .. code-block:: python
+
+     # OLD (hardcoded 95-150°F)
+     await mqtt.control.set_dhw_temperature(device, temperature_f=140.0)
+     entry = build_reservation_entry(
+         enabled=True,
+         days=["Monday"],
+         hour=6,
+         minute=0,
+         mode_id=3,
+         temperature_f=140.0,
+     )
+
+     # NEW (device-provided limits, unit-aware)
+     # Temperature value automatically uses user's preferred unit
+     await mqtt.control.set_dhw_temperature(device, 140.0)
+     
+     # Device features provide min/max in user's preferred unit
+     features = await device_info_cache.get(device.device_info.mac_address)
+     entry = build_reservation_entry(
+         enabled=True,
+         days=["Monday"],
+         hour=6,
+         minute=0,
+         mode_id=3,
+         temperature=140.0,
+         temperature_min=features.dhw_temperature_min,
+         temperature_max=features.dhw_temperature_max,
+     )
+
+Added
+-----
+- **Reservation Temperature Conversion**: New ``reservation_param_to_preferred()`` utility function for unit-aware reservation display
+
+  - Converts device reservation parameters (half-degree Celsius) to user's preferred unit
+  - Respects global unit system context (metric/us_customary)
+  - Enables proper thermostat/reservation scheduling display in Home Assistant and other integrations
+  - Example usage:
+
+  .. code-block:: python
+
+     from nwp500 import reservation_param_to_preferred
+
+     # Display reservation temperature in user's preferred unit
+     param = 120  # Device raw value in half-Celsius
+     temp = reservation_param_to_preferred(param)
+     # Returns: 60.0 (Celsius) or 140.0 (Fahrenheit) based on unit context
+
+- **Unit-Aware Temperature Conversion**: New ``preferred_to_half_celsius()`` utility function
+
+  - Converts temperature from user's preferred unit to half-degree Celsius for device commands
+  - Respects global unit system context (metric/us_customary)
+  - Replaces misleading ``fahrenheit_to_half_celsius()`` in unit-agnostic code paths
+  - Used internally by ``set_dhw_temperature()`` and ``build_reservation_entry()``
+
+Changed
+-------
+- **Unit System Agnostic Display**: All logging and user-facing messages now respect global unit system context
+
+  - Temperature change logs dynamically show °C or °F based on user preference
+  - CLI monitoring and temperature setting messages use correct unit suffix
+  - Event listener documentation updated with unit-aware examples
+  - Reservation schedule examples now use ``reservation_param_to_preferred()`` for proper unit handling
+
+Fixed
+-----
+- **Critical: Temperature Unit Bug in Set Operations**: Fixed incorrect temperature conversion when setting DHW temperature and reservations
+
+  - ``set_dhw_temperature()`` was calling ``fahrenheit_to_half_celsius()`` with unit-agnostic temperature parameter
+  - ``build_reservation_entry()`` had the same issue
+  - **Impact**: If user preferred Celsius, temperature would be interpreted as Fahrenheit, causing wrong setpoints
+  - **Fix**: Use new ``preferred_to_half_celsius()`` that respects unit system context
+  - This was a critical data correctness bug that would cause incorrect device behavior for Celsius users
+
 Version 7.3.2 (2026-01-25)
 ==========================
 
diff --git a/docs/protocol/mqtt_protocol.rst b/docs/protocol/mqtt_protocol.rst
index b35b20e..683a2cd 100644
--- a/docs/protocol/mqtt_protocol.rst
+++ b/docs/protocol/mqtt_protocol.rst
@@ -422,7 +422,7 @@ DHW Temperature
    Temperature values are encoded in **half-degrees Celsius**. 
    Use formula: ``fahrenheit = (param / 2.0) * 9/5 + 32``
    For 140°F, send ``param=120`` (which is 60°C × 2).
-   Valid range: 95-150°F (70-150 raw value).
+   Valid range: Device-specific (see device features for ``dhw_temperature_min`` and ``dhw_temperature_max``).
 
 Anti-Legionella
 ---------------
diff --git a/examples/advanced/combined_callbacks.py b/examples/advanced/combined_callbacks.py
index 259731b..bd6fd4f 100644
--- a/examples/advanced/combined_callbacks.py
+++ b/examples/advanced/combined_callbacks.py
@@ -98,8 +98,11 @@ def on_feature(feature: DeviceFeature):
                     print(f"\n📋 Feature Info #{counts['feature']}")
                     print(f"  Serial: {feature.controller_serial_number}")
                     print(f"  FW Version: {feature.controller_sw_version}")
+                    unit_suffix = (
+                        "°C" if feature.temperature_type.name == "CELSIUS" else "°F"
+                    )
                     print(
-                        f"  Temp Range: {feature.dhw_temperature_min}-{feature.dhw_temperature_max}°F"
+                        f"  Temp Range: {feature.dhw_temperature_min}-{feature.dhw_temperature_max}{unit_suffix}"
                     )
                     print(
                         f"  Heat Pump: {'Yes' if feature.heatpump_use == OnOffFlag.ON else 'No'}"
diff --git a/examples/advanced/device_capabilities.py b/examples/advanced/device_capabilities.py
index e7c88e8..e5f1e18 100644
--- a/examples/advanced/device_capabilities.py
+++ b/examples/advanced/device_capabilities.py
@@ -138,13 +138,16 @@ def on_device_feature(feature: DeviceFeature):
                     )
 
                     print("\nConfiguration:")
+                    unit_suffix = (
+                        "°C" if feature.temperature_type.name == "CELSIUS" else "°F"
+                    )
                     print(f"  Temperature Unit:   {feature.temperature_type.name}")
                     print(f"  Temp Formula Type:  {feature.temp_formula_type}")
                     print(
-                        f"  DHW Temp Range:     {feature.dhw_temperature_min}°F - {feature.dhw_temperature_max}°F"
+                        f"  DHW Temp Range:     {feature.dhw_temperature_min}{unit_suffix} - {feature.dhw_temperature_max}{unit_suffix}"
                     )
                     print(
-                        f"  Freeze Prot Range:  {feature.freeze_protection_temp_min}°F - {feature.freeze_protection_temp_max}°F"
+                        f"  Freeze Prot Range:  {feature.freeze_protection_temp_min}{unit_suffix} - {feature.freeze_protection_temp_max}{unit_suffix}"
                     )
 
                     print("\nFeature Support:")
diff --git a/examples/advanced/reservation_schedule.py b/examples/advanced/reservation_schedule.py
index 4423d6d..fcc67ec 100644
--- a/examples/advanced/reservation_schedule.py
+++ b/examples/advanced/reservation_schedule.py
@@ -32,7 +32,7 @@ async def main() -> None:
             hour=6,
             minute=30,
             mode_id=4,  # High Demand
-            temperature_f=140.0,  # Temperature in Fahrenheit
+            temperature=140.0,  # Temperature in user's preferred unit
         )
 
         mqtt_client = NavienMqttClient(auth_client)
@@ -42,6 +42,9 @@ async def main() -> None:
         response_topic = f"cmd/{device.device_info.device_type}/{mqtt_client.config.client_id}/res/rsv/rd"
 
         def on_reservation_update(topic: str, message: dict[str, Any]) -> None:
+            from nwp500 import reservation_param_to_preferred
+            from nwp500.unit_system import get_unit_system
+
             response = message.get("response", {})
             reservations = response.get("reservation", [])
             print("\nReceived reservation response:")
@@ -49,18 +52,21 @@ def on_reservation_update(topic: str, message: dict[str, Any]) -> None:
                 f"  reservationUse: {response.get('reservationUse')} (1=enabled, 2=disabled)"
             )
             print(f"  entries: {len(reservations)}")
+            unit_suffix = "°C" if get_unit_system() == "metric" else "°F"
             for idx, entry in enumerate(reservations, start=1):
                 week_days = decode_week_bitfield(entry.get("week", 0))
-                # Convert half-degrees Celsius param back to Fahrenheit for display
+                # Convert half-degrees Celsius param to user's preferred unit
                 param = entry.get("param", 0)
-                temp_f = (param / 2.0) * 9 / 5 + 32
+                temp = reservation_param_to_preferred(param)
                 print(
-                    "   - #{idx}: {time:02d}:{minute:02d} mode={mode} temp={temp:.1f}°F days={days}".format(
+                    "   - #{idx}: {time:02d}:{minute:02d} mode={mode} "
+                    "temp={temp:.1f}{unit} days={days}".format(
                         idx=idx,
                         time=entry.get("hour", 0),
                         minute=entry.get("min", 0),
                         mode=entry.get("mode"),
-                        temp=temp_f,
+                        temp=temp,
+                        unit=unit_suffix,
                         days=", ".join(week_days) or "<none>",
                     )
                 )
diff --git a/src/nwp500/__init__.py b/src/nwp500/__init__.py
index b38444d..d309c4d 100644
--- a/src/nwp500/__init__.py
+++ b/src/nwp500/__init__.py
@@ -113,6 +113,8 @@
     TOUInfo,
     TOUSchedule,
     fahrenheit_to_half_celsius,
+    preferred_to_half_celsius,
+    reservation_param_to_preferred,
 )
 from nwp500.mqtt import (
     ConnectionDropEvent,
@@ -179,6 +181,8 @@
     "VolumeCode",
     # Conversion utilities
     "fahrenheit_to_half_celsius",
+    "preferred_to_half_celsius",
+    "reservation_param_to_preferred",
     # Authentication
     "NavienAuthClient",
     "AuthenticationResponse",
diff --git a/src/nwp500/cli/handlers.py b/src/nwp500/cli/handlers.py
index 6440dea..5d2dc64 100644
--- a/src/nwp500/cli/handlers.py
+++ b/src/nwp500/cli/handlers.py
@@ -22,6 +22,7 @@
     ValidationError,
 )
 from nwp500.mqtt.utils import redact_serial
+from nwp500.unit_system import get_unit_system
 
 from .output_formatters import (
     print_device_info,
@@ -239,12 +240,13 @@ async def handle_set_dhw_temp_request(
     mqtt: NavienMqttClient, device: Device, temperature: float
 ) -> None:
     """Set DHW target temperature."""
+    unit_suffix = "°C" if get_unit_system() == "metric" else "°F"
     await _handle_command_with_status_feedback(
         mqtt,
         device,
         lambda: mqtt.control.set_dhw_temperature(device, temperature),
         "setting temperature",
-        f"Temperature set to {temperature}°F",
+        f"Temperature set to {temperature}{unit_suffix}",
     )
 
 
diff --git a/src/nwp500/cli/monitoring.py b/src/nwp500/cli/monitoring.py
index 90cde4d..371a88f 100644
--- a/src/nwp500/cli/monitoring.py
+++ b/src/nwp500/cli/monitoring.py
@@ -4,6 +4,7 @@
 import logging
 
 from nwp500 import Device, DeviceStatus, NavienMqttClient
+from nwp500.unit_system import get_unit_system
 
 from .output_formatters import write_status_to_csv
 
@@ -30,8 +31,10 @@ async def handle_monitoring(
     _logger.info("Press Ctrl+C to stop.")
 
     def on_status_update(status: DeviceStatus) -> None:
+        unit_suffix = "°C" if get_unit_system() == "metric" else "°F"
         _logger.info(
-            f"Received status update: Temp={status.dhw_temperature}°F, "
+            f"Received status update: Temp={status.dhw_temperature}"
+            f"{unit_suffix}, "
             f"Power={'ON' if status.dhw_use else 'OFF'}"
         )
         write_status_to_csv(output_file, status)
diff --git a/src/nwp500/encoding.py b/src/nwp500/encoding.py
index e79666b..6c087fc 100644
--- a/src/nwp500/encoding.py
+++ b/src/nwp500/encoding.py
@@ -326,7 +326,9 @@ def build_reservation_entry(
     hour: int,
     minute: int,
     mode_id: int,
-    temperature_f: float,
+    temperature: float,
+    temperature_min: float | None = None,
+    temperature_max: float | None = None,
 ) -> dict[str, int]:
     """
     Build a reservation payload entry matching the documented MQTT format.
@@ -337,8 +339,13 @@ def build_reservation_entry(
         hour: Hour (0-23)
         minute: Minute (0-59)
         mode_id: DHW operation mode ID (1-6, see DhwOperationSetting)
-        temperature_f: Target temperature in Fahrenheit (95-150°F).
+        temperature: Target temperature in the user's preferred unit
+            (Celsius or Fahrenheit based on global context).
             Automatically converted to half-degrees Celsius for the device.
+        temperature_min: Minimum allowed temperature. If not provided,
+            defaults are used: 95°F or ~35°C.
+        temperature_max: Maximum allowed temperature. If not provided,
+            defaults are used: 150°F or ~65°C.
 
     Returns:
         Dictionary with reservation entry fields
@@ -355,12 +362,17 @@ def build_reservation_entry(
         ...     hour=6,
         ...     minute=30,
         ...     mode_id=3,
-        ...     temperature_f=140.0
+        ...     temperature=140.0
         ... )
         {'enable': 1, 'week': 42, 'hour': 6, 'min': 30, 'mode': 3, 'param': 120}
     """
     # Import here to avoid circular import
-    from .models import fahrenheit_to_half_celsius
+    from .models import preferred_to_half_celsius
+
+    # Use device-provided limits if available, otherwise use defaults
+    # Defaults are conservative: 95°F / 35°C minimum, 150°F / 65°C maximum
+    min_temp = temperature_min if temperature_min is not None else 95
+    max_temp = temperature_max if temperature_max is not None else 150
 
     if not 0 <= hour <= 23:
         raise RangeValidationError(
@@ -386,13 +398,13 @@ def build_reservation_entry(
             min_value=1,
             max_value=6,
         )
-    if not 95 <= temperature_f <= 150:
+    if not min_temp <= temperature <= max_temp:
         raise RangeValidationError(
-            "temperature_f must be between 95 and 150°F",
-            field="temperature_f",
-            value=temperature_f,
-            min_value=95,
-            max_value=150,
+            f"temperature must be between {min_temp} and {max_temp}",
+            field="temperature",
+            value=temperature,
+            min_value=min_temp,
+            max_value=max_temp,
         )
 
     if isinstance(enabled, bool):
@@ -407,7 +419,7 @@ def build_reservation_entry(
         )
 
     week_bitfield = encode_week_bitfield(days)
-    param = fahrenheit_to_half_celsius(temperature_f)
+    param = preferred_to_half_celsius(temperature)
 
     return {
         "enable": enable_flag,
diff --git a/src/nwp500/events.py b/src/nwp500/events.py
index d37ea28..69b64b2 100644
--- a/src/nwp500/events.py
+++ b/src/nwp500/events.py
@@ -83,8 +83,11 @@ def on(
 
         Example::
 
+            from nwp500.unit_system import get_unit_system
+
             def on_temp_change(old_temp: float, new_temp: float):
-                print(f"Temperature: {old_temp}°F → {new_temp}°F")
+                unit = "°C" if get_unit_system() == "metric" else "°F"
+                print(f"Temperature: {old_temp}{unit} → {new_temp}{unit}")
 
             emitter.on('temperature_changed', on_temp_change)
 
diff --git a/src/nwp500/models.py b/src/nwp500/models.py
index 2c480d8..db63edd 100644
--- a/src/nwp500/models.py
+++ b/src/nwp500/models.py
@@ -108,6 +108,63 @@ def fahrenheit_to_half_celsius(fahrenheit: float) -> int:
     return int(HalfCelsius.from_fahrenheit(fahrenheit).raw_value)
 
 
+def preferred_to_half_celsius(temperature: float) -> int:
+    """Convert temperature from preferred unit to half-degrees Celsius.
+
+    Converts temperature from the user's preferred unit (Celsius or Fahrenheit,
+    based on global unit system context) to the half-Celsius format used by
+    the device for commands and reservations.
+
+    Args:
+        temperature: Temperature in user's preferred unit
+            (Celsius or Fahrenheit).
+
+    Returns:
+        Raw device value in half-Celsius format.
+
+    Example:
+        >>> # With us_customary unit system
+        >>> preferred_to_half_celsius(140.0)  # 140°F
+        120
+        >>> # With metric unit system
+        >>> preferred_to_half_celsius(60.0)  # 60°C
+        120
+    """
+    if get_unit_system() == "metric":
+        # User prefers Celsius, input is in Celsius
+        return int(HalfCelsius.from_celsius(temperature).raw_value)
+    else:
+        # User prefers Fahrenheit (or no preference), input is in Fahrenheit
+        return fahrenheit_to_half_celsius(temperature)
+
+
+def reservation_param_to_preferred(param: int) -> float:
+    """Convert reservation param to user's preferred temperature unit.
+
+    Device returns reservation temperatures as half-degrees Celsius (param).
+    This converts them to the user's preferred unit (Celsius or Fahrenheit)
+    based on the global unit system context.
+
+    Args:
+        param: Raw device value in half-Celsius format.
+
+    Returns:
+        Temperature in user's preferred unit (Celsius or Fahrenheit).
+
+    Example:
+        >>> # With metric (Celsius) unit system
+        >>> reservation_param_to_preferred(120)
+        60.0
+        >>> # With us_customary (Fahrenheit) unit system
+        >>> reservation_param_to_preferred(120)
+        140.0
+    """
+    half_celsius = HalfCelsius(param)
+    if get_unit_system() == "metric":
+        return round(half_celsius.to_celsius(), 1)
+    return round(half_celsius.to_fahrenheit(), 1)
+
+
 class NavienBaseModel(BaseModel):
     """Base model for all Navien models.
 
diff --git a/src/nwp500/mqtt/control.py b/src/nwp500/mqtt/control.py
index 43effd2..f3e9e9e 100644
--- a/src/nwp500/mqtt/control.py
+++ b/src/nwp500/mqtt/control.py
@@ -31,7 +31,11 @@
     ParameterValidationError,
     RangeValidationError,
 )
-from ..models import Device, DeviceFeature, fahrenheit_to_half_celsius
+from ..models import (
+    Device,
+    DeviceFeature,
+    preferred_to_half_celsius,
+)
 from ..topic_builder import MqttTopicBuilder
 
 __author__ = "Emmanuel Levijarvi"
@@ -395,15 +399,34 @@ async def disable_anti_legionella(self, device: Device) -> int:
 
     @requires_capability("dhw_temperature_setting_use")
     async def set_dhw_temperature(
-        self, device: Device, temperature_f: float
+        self, device: Device, temperature: float
     ) -> int:
-        """Set DHW target temperature (95-150°F)."""
-        self._validate_range("temperature_f", temperature_f, 95, 150)
+        """Set DHW target temperature.
+
+        Temperature is in the user's preferred unit (Celsius or Fahrenheit)
+        based on the global unit system context.
+        """
+        features = await self._get_device_features(device)
+        if features is None:
+            raise DeviceCapabilityError(
+                "dhw_temperature_setting_use",
+                (
+                    "Device features not available. "
+                    "Unable to validate temperature range."
+                ),
+            )
+
+        self._validate_range(
+            "temperature",
+            temperature,
+            features.dhw_temperature_min,
+            features.dhw_temperature_max,
+        )
         return await self._mode_command(
             device,
             CommandCode.DHW_TEMPERATURE,
             "dhw-temperature",
-            [fahrenheit_to_half_celsius(temperature_f)],
+            [preferred_to_half_celsius(temperature)],
         )
 
     async def update_reservations(
diff --git a/src/nwp500/mqtt/subscriptions.py b/src/nwp500/mqtt/subscriptions.py
index bfb5cf8..2c1823a 100644
--- a/src/nwp500/mqtt/subscriptions.py
+++ b/src/nwp500/mqtt/subscriptions.py
@@ -25,7 +25,7 @@
 from ..exceptions import MqttNotConnectedError
 from ..models import Device, DeviceFeature, DeviceStatus, EnergyUsageResponse
 from ..topic_builder import MqttTopicBuilder
-from ..unit_system import UnitSystemType, set_unit_system
+from ..unit_system import UnitSystemType, get_unit_system, set_unit_system
 from .utils import redact_topic, topic_matches_pattern
 
 if TYPE_CHECKING:
@@ -428,9 +428,10 @@ async def _detect_state_changes(self, status: DeviceStatus) -> None:
                     prev.dhw_temperature,
                     status.dhw_temperature,
                 )
+                unit_suffix = "°C" if get_unit_system() == "metric" else "°F"
                 _logger.debug(
-                    f"Temperature changed: {prev.dhw_temperature}°F → "
-                    f"{status.dhw_temperature}°F"
+                    f"Temperature changed: {prev.dhw_temperature}"
+                    f"{unit_suffix} → {status.dhw_temperature}{unit_suffix}"
                 )
 
             # Operation mode change
diff --git a/src/nwp500/mqtt_events.py b/src/nwp500/mqtt_events.py
index 087196e..6276d47 100644
--- a/src/nwp500/mqtt_events.py
+++ b/src/nwp500/mqtt_events.py
@@ -11,12 +11,14 @@
 Example::
 
     from nwp500.mqtt_events import MqttClientEvents
+    from nwp500.unit_system import get_unit_system
 
     # Type-safe event listening with autocomplete
-    mqtt_client.on(
-        MqttClientEvents.TEMPERATURE_CHANGED,
-        lambda old_temp, new_temp: print(f"Temp: {old_temp}°F → {new_temp}°F")
-    )
+    def on_temperature_changed(old_temp, new_temp):
+        unit = "°C" if get_unit_system() == "metric" else "°F"
+        print(f"Temp: {old_temp}{unit} → {new_temp}{unit}")
+
+    mqtt_client.on(MqttClientEvents.TEMPERATURE_CHANGED, on_temperature_changed)
 
     # List all available events
     for event_name in MqttClientEvents.get_all_events():
@@ -71,8 +73,10 @@ class TemperatureChangedEvent:
     """Emitted when the DHW temperature changes.
 
     Attributes:
-        old_temperature: Previous DHW temperature in °F
-        new_temperature: New DHW temperature in °F
+        old_temperature: Previous DHW temperature in user's preferred unit
+            (Celsius or Fahrenheit based on unit system context)
+        new_temperature: New DHW temperature in user's preferred unit
+            (Celsius or Fahrenheit based on unit system context)
     """
 
     old_temperature: float
@@ -221,8 +225,10 @@ class MqttClientEvents:
     """Emitted: DHW temperature changed.
 
     Args:
-        old_temperature (float): Previous DHW temperature (°F)
-        new_temperature (float): New DHW temperature (°F)
+        old_temperature (float): Previous DHW temperature in user's
+            preferred unit
+        new_temperature (float): New DHW temperature in user's preferred
+            unit
 
     See: :class:`TemperatureChangedEvent`
     """
diff --git a/tests/test_api_helpers.py b/tests/test_api_helpers.py
index 93514f0..84a0bc7 100644
--- a/tests/test_api_helpers.py
+++ b/tests/test_api_helpers.py
@@ -68,7 +68,7 @@ def test_build_reservation_entry():
         hour=6,
         minute=30,
         mode_id=4,
-        temperature_f=140.0,
+        temperature=140.0,
     )
 
     assert reservation["enable"] == 1
@@ -85,7 +85,7 @@ def test_build_reservation_entry():
         hour=8,
         minute=0,
         mode_id=3,
-        temperature_f=120.0,
+        temperature=120.0,
     )
     assert reservation2["param"] == 98  # 120°F ≈ 48.9°C ≈ 98 half-degrees
 
@@ -96,7 +96,7 @@ def test_build_reservation_entry():
             hour=24,
             minute=0,
             mode_id=1,
-            temperature_f=120.0,
+            temperature=120.0,
         )
 
     # Test temperature out of range
@@ -107,7 +107,7 @@ def test_build_reservation_entry():
             hour=6,
             minute=0,
             mode_id=1,
-            temperature_f=200.0,  # Too high
+            temperature=200.0,  # Too high
         )