diff --git a/tests/test_coordinator.py b/tests/test_coordinator.py
index a88c10e..0f194e9 100644
--- a/tests/test_coordinator.py
+++ b/tests/test_coordinator.py
@@ -1033,3 +1033,36 @@ class BoundaryTests(unittest.IsolatedAsyncioTestCase):
         for zone, other in (('living', 'bed'), ('bed', 'living')):
             with self.subTest(zone=zone):
                 self.assertLess(c.extended[zone].coefficient(f'couple:{other}'), 0.002)
+
+    async def test_new_model_layers_survive_a_restart(self):
+        self.c = self.bedroom_with_window()
+        self.c.entry.subentries['h'] = types.SimpleNamespace(subentry_id='h', subentry_type='heat_source', data={
+            'key': 'ups', 'name': 'UPS', 'sensor': 'sensor.ups_power', 'zone': 'bed'})
+        self.set_state('sensor.ups_power', '200', unit_of_measurement='W')
+        self.c = coordinator.HeatingMPCCoordinator(self.hass, self.entry)
+        for k in range(20):
+            self.fresh('sensor.room', 'sensor.outside', 'sensor.wind', 'sensor.wind_dir', 'sensor.ups_power')
+            if k == 18:
+                self.open_window('on', 240)
+            await self.sample()
+        extended, vent = self.c.extended['bed'], self.c.ventilation['bed']
+        self.assertGreater(extended.count, 0)
+        self.assertGreater(vent.count, 0)
+        payload = self.c._store.async_save.call_args.args[0]
+        restored = coordinator.HeatingMPCCoordinator(self.hass, self.entry)
+        restored._store.async_load.return_value = payload
+        await restored.async_restore_model()
+        self.assertEqual((restored.extended['bed'].theta, restored.extended['bed'].count), (extended.theta, extended.count))
+        self.assertEqual((restored.ventilation['bed'].theta, restored.ventilation['bed'].count), (vent.theta, vent.count))
+        self.assertEqual(restored._heat_sources._baselines['ups'].value(), 200)  # no hour of re-learning
+        # Adding a feature keeps what was learned for the others.
+        self.entry.data['ventilation_cross'] = True
+        self.entry.subentries['z2'] = types.SimpleNamespace(subentry_id='z2', subentry_type='zone', data={
+            'key': 'living', 'name': 'Living', 'sensors': ['sensor.living']})
+        self.entry.subentries['w2'] = types.SimpleNamespace(subentry_id='w2', subentry_type='window', data={
+            'key': 'living_window', 'name': 'Living window', 'sensor': 'binary_sensor.living_window', 'zone': 'living'})
+        grown = coordinator.HeatingMPCCoordinator(self.hass, self.entry)
+        grown._store.async_load.return_value = payload
+        await grown.async_restore_model()
+        self.assertEqual(grown.ventilation['bed'].features[-1], 'vent_cross')
+        self.assertEqual(grown.ventilation['bed'].theta[:-1], vent.theta)
diff --git a/tests/test_heat_sources.py b/tests/test_heat_sources.py
index f88380a..ec3b58e 100644
--- a/tests/test_heat_sources.py
+++ b/tests/test_heat_sources.py
@@ -93,6 +93,14 @@ class TrackerTests(unittest.TestCase):
         self.assertEqual(tracker.zone_input('office'), states[-1]['ups']['response_kw'])
         self.assertEqual(tracker.zone_input('living'), 0.0)
 
+    def test_short_spike_barely_moves_response_or_baseline(self):
+        tracker = hs.HeatSourceTracker(sources(UPS), {'baselines': {'ups': [200.0] * 24}})
+        states = run(tracker, [{'ups': 200.0}] * 3 + [{'ups': 900.0}] + [{'ups': 200.0}] * 4)
+        peak = max(s['ups']['response_kw'] for s in states)
+        self.assertAlmostEqual(peak, 0.7 * (1 - exp(-1 / 3)))  # one 5-minute interval of +700 W
+        self.assertLess(peak, 0.2)
+        self.assertEqual(states[-1]['ups']['baseline_w'], 200)
+
     def test_unknown_power_resets_until_settled_again(self):
         tracker = hs.HeatSourceTracker(sources(UPS), {'baselines': {'ups': [200.0] * 24}})
         run(tracker, [{'ups': 200.0}] * 7)
diff --git a/tests/test_windows.py b/tests/test_windows.py
index 9728048..dfc1e01 100644
--- a/tests/test_windows.py
+++ b/tests/test_windows.py
@@ -55,6 +55,10 @@ class GeometryTests(unittest.TestCase):
                                    [-9.0, -36.0, 21.6, -45.0, -9.0, 0.0]):
             self.assertAlmostEqual(value, expected)
         self.assertIsNone(wm.ventilation_vector(['vent_wind'], 20, 2, {**inputs, 'wind': None}))
+        # Calm air: wind terms vanish, natural ventilation stays.
+        calm = wm.ventilation_vector(features, 20.0, 2.0, {**inputs, 'wind': 0.0, 'gust': 0.0})
+        self.assertEqual([round(v, 9) for v in calm[1:4]], [0.0, 0.0, 0.0])
+        self.assertEqual(calm[0], -9.0)
         self.assertEqual(wm.ventilation_vector(['vent_natural'], 20, 2, {**inputs, 'wind': None}), [-9.0])
         self.assertIsNone(wm.ventilation_vector(['recovery'], 20, 2, {**inputs, 'recovery': 0.5}))
         self.assertEqual(wm.ventilation_vector(['recovery'], 19, 2, {**inputs, 'recovery': 0.5, 't_ref': 21}),