diff --git a/datatypes/epc/domain/mapper.py b/datatypes/epc/domain/mapper.py
index 8ed8c1b5..fa72cfe5 100644
--- a/datatypes/epc/domain/mapper.py
+++ b/datatypes/epc/domain/mapper.py
@@ -1561,5 +1561,6 @@ def _map_sap_heating(
         has_fixed_air_conditioning=ventilation.has_fixed_air_conditioning,
         secondary_fuel_type=secondary_fuel_type,
         shower_outlets=shower_outlets,
+        cylinder_size=heating.water_heating.cylinder_size if heating.water_heating.cylinder_size != "No Cylinder" else None,
         cylinder_insulation_thickness_mm=heating.water_heating.insulation_thickness_mm,
     )