diff --git a/cara/models.py b/cara/models.py
index 3d9a730e..d761b0c3 100644
--- a/cara/models.py
+++ b/cara/models.py
@@ -271,7 +271,7 @@ class WindowOpening(Ventilation):
     min_deltaT: float = 0.1
 
     @property
-    def discharge_coefficient(self) -> float:
+    def discharge_coefficient(self) -> _VectorisedFloat:
         """
         Discharge coefficient (or cd_b): what portion effective area is
         used to exchange air (0 <= discharge_coefficient <= 1).
@@ -291,14 +291,14 @@ class WindowOpening(Ventilation):
             return 0.
 
         # Reminder, no dependence on time in the resulting calculation.
-        inside_temp = self.inside_temp.value(time)
-        outside_temp = self.outside_temp.value(time)
+        inside_temp: _VectorisedFloat = self.inside_temp.value(time)
+        outside_temp: _VectorisedFloat = self.outside_temp.value(time)
 
         # The inside_temperature is forced to be always at least min_deltaT degree
         # warmer than the outside_temperature. Further research needed to
         # handle the buoyancy driven ventilation when the temperature gradient
         # is inverted.
-        inside_temp = max(inside_temp, outside_temp + self.min_deltaT)
+        inside_temp = np.maximum(inside_temp, outside_temp + self.min_deltaT)  # type: ignore
         temp_gradient = (inside_temp - outside_temp) / outside_temp
         root = np.sqrt(9.81 * self.window_height * temp_gradient)
         window_area = self.window_height * self.opening_length * self.number_of_windows
@@ -312,7 +312,7 @@ class SlidingWindow(WindowOpening):
     the horizontal plane).
     """
     @property
-    def discharge_coefficient(self) -> float:
+    def discharge_coefficient(self) -> _VectorisedFloat:
         """
         Average measured value of discharge coefficient for sliding or
         side-hung windows.
@@ -334,7 +334,7 @@ class HingedWindow(WindowOpening):
             raise ValueError('window_width must be set')
 
     @property
-    def discharge_coefficient(self) -> float:
+    def discharge_coefficient(self) -> _VectorisedFloat:
         """
         Simple model to compute discharge coefficient for top or bottom
         hung hinged windows, in the absence of empirical test results
@@ -351,7 +351,7 @@ class HingedWindow(WindowOpening):
         coefs[np.bitwise_and(0.5 <= window_ratio, window_ratio < 1)] = (0.048, 0.589)
         coefs[np.bitwise_and(1 <= window_ratio, window_ratio < 2)] = (0.04, 0.563)
         coefs[window_ratio >= 2] = (0.038, 0.548)
-        M, cd_max = coefs
+        M, cd_max = coefs.T
 
         window_angle = 2.*np.rad2deg(np.arcsin(self.opening_length/(2.*self.window_height)))
         return cd_max*(1-np.exp(-M*window_angle))
diff --git a/cara/tests/test_ventilation.py b/cara/tests/test_ventilation.py
index 624203ef..f10a6263 100644
--- a/cara/tests/test_ventilation.py
+++ b/cara/tests/test_ventilation.py
@@ -57,14 +57,15 @@ def test_hinged_window(baseline_hingedwindow, window_width,
 
 @pytest.mark.parametrize(
     "override_params", [
-        {'window_height': np.array([0.15, 0.20])},
-        {'window_width': np.array([0.15, 0.20])},
-        {'opening_length': np.array([0.15, 0.20])},
+        {'window_height': np.array([0.15, 0.20, 0.25])},
+        {'window_width': np.array([0.15, 0.20, 0.25])},
+        {'opening_length': np.array([0.15, 0.20, 0.25])},
         {'outside_temp': models.PiecewiseConstant(
-            (1, 2, 3), (np.array([20, 30]), np.array([25, 30]))),
-        },
-        {'outside_temp': np.array([20, 30])},
-        {'inside_temp': np.array([20, 30])},
+            (0, 2, 3), (np.array([20, 30, 28]), np.array([25, 30, 27]))
+        )},
+        {'inside_temp': models.PiecewiseConstant(
+            (0, 20), (np.array([20, 30, 25]), )
+        )},
     ]
 )
 def test_HingedWindow_vectorisation(override_params):
@@ -72,17 +73,20 @@ def test_HingedWindow_vectorisation(override_params):
         'window_height': 0.15,
         'window_width': 0.15,
         'opening_length': 0.15,
-        'inside_temp': 20,
-        'outside_temp': 10,
+        'inside_temp': models.PiecewiseConstant((0, 2, 3), (20, 25)),
+        'outside_temp': models.PiecewiseConstant((0, 2, 3), (10, 15)),
     }
     defaults.update(override_params)
-
+    room = models.Room(volume=75)
+    t = 0.5
     window = models.HingedWindow(models.PeriodicInterval(60, 30), **defaults)
     if {'window_height', 'opening_length', 'window_width'}.intersection(override_params):
         assert isinstance(window.discharge_coefficient, np.ndarray)
     else:
         assert isinstance(window.discharge_coefficient, float)
 
+    assert isinstance(window.air_exchange(room, t), np.ndarray)
+
 
 def test_sliding_window(baseline_slidingwindow):
     assert baseline_slidingwindow.discharge_coefficient == 0.6