diff --git a/exports/energy_systems/heat_pump_export.py b/exports/energy_systems/heat_pump_export.py
index e5828608..3f5b9c73 100644
--- a/exports/energy_systems/heat_pump_export.py
+++ b/exports/energy_systems/heat_pump_export.py
@@ -215,7 +215,7 @@ class HeatPumpExport:
 
     data = [electricity_df, fossil_df]
     df = pd.concat(data, axis=1)
-    df = df.append(df.agg(['sum']))
+    df = pd.concat([df, df.agg(['sum'])])
     s = pd.Series(["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sept", "Oct", "Nov", "Dec", "Total"])
     df = df.set_index([s])
     df.to_csv(self._output_path)