diff --git a/etl/epc/generate_scenarios_data.py b/etl/epc/generate_scenarios_data.py
index b61618b1..f1406759 100644
--- a/etl/epc/generate_scenarios_data.py
+++ b/etl/epc/generate_scenarios_data.py
@@ -65,7 +65,7 @@ scenario_properties = [
             ],
             [
                 ["external_wall_insulation"],
-                "10",
+                "11",
                 {},
                 [0],
             ],
diff --git a/recommendations/WindowsRecommendations.py b/recommendations/WindowsRecommendations.py
index 343965e3..1f755369 100644
--- a/recommendations/WindowsRecommendations.py
+++ b/recommendations/WindowsRecommendations.py
@@ -127,12 +127,12 @@ class WindowsRecommendations:
                 )
 
         # Set up the simulation config
+        windows_energy_eff = "Good"
         if self.property.windows["glazing_type"] == "multiple":
             glazing_type_ending = "multiple"
             glazed_type_ending = (
                 "secondary glazing" if is_secondary_glazing else "double glazing installed during or after 2002"
             )
-            windows_energy_eff = "Good"
             new_windows_description = "Multiple glazing throughout"
 
         elif self.property.windows["glazing_type"] == "single":
@@ -145,10 +145,8 @@ class WindowsRecommendations:
             )
 
             if is_secondary_glazing:
-                windows_energy_eff = "Good"
                 new_windows_description = "Full secondary glazing"
             else:
-                windows_energy_eff = "Average"
                 new_windows_description = "Fully double glazed"
 
         elif self.property.windows["glazing_type"] == "double":
@@ -164,7 +162,6 @@ class WindowsRecommendations:
             if not is_secondary_glazing:
                 glazed_type_ending = "double glazing installed during or after 2002"
                 new_windows_description = "Fully double glazed"
-                windows_energy_eff = "Average"
             else:
                 if self.property.data["multi-glaze-proportion"] < 50:
                     glazed_type_ending = "secondary glazing"
@@ -172,13 +169,11 @@ class WindowsRecommendations:
                     glazed_type_ending = "double glazing installed during or after 2002"
 
                 new_windows_description = "Multiple glazing throughout"
-                windows_energy_eff = "Good"
 
         elif self.property.windows["glazing_type"] == "secondary":
             glazing_type_ending = (
                 "secondary" if is_secondary_glazing else "multiple"
             )
-            windows_energy_eff = "Good"
             # This is the opposite. If there is secondary glazing in place, and we're recommending double
             # we set glazed_type_ending, depending on the proportion of glazing in place
             if is_secondary_glazing:
@@ -194,8 +189,10 @@ class WindowsRecommendations:
         else:
             raise ValueError("Invalid glazing type - implement me")
 
-        if (self.property.data["windows-energy-eff"] in ["Good", "Very Good"]) and (windows_energy_eff == "Average"):
-            windows_energy_eff = self.property.data["windows-energy-eff"]
+        if self.property.data["windows-energy-eff"] == "Very Good":
+            raise ValueError("Very Good energy efficiency is not supported")
+
+        # For post 2002 windows, the energy efficiency is "Good" and so for the simulation, we simulate with "Good"
 
         windows_ending_config = WindowAttributes(new_windows_description).process()