diff --git a/datatypes/epc/domain/mapper.py b/datatypes/epc/domain/mapper.py
index 26704922..51cffde3 100644
--- a/datatypes/epc/domain/mapper.py
+++ b/datatypes/epc/domain/mapper.py
@@ -72,10 +72,9 @@ _SAP_KNOWN_WALL_TYPES: Final[frozenset[int]] = frozenset({1, 2, 3, 4, 5})
 # RdSAP age band M. Used only for that fallback + secondary age-band logic.
 _SAP_DEFAULT_AGE_BAND: Final[str] = "M"
 # full-SAP standard `ventilation_type` code → MechanicalVentilationKind name
-# (None = natural). MVHR (7) is deferred to natural — like the RdSAP API path
-# (_API_MECHANICAL_VENTILATION_TO_KIND code 4), its (24a) formula needs the
-# PCDB heat-recovery efficiency, not yet plumbed; mapping to MVHR with a null
-# efficiency would mis-model it as MV. None of the corpus lodges 7.
+# (None = natural). MVHR (code 8) uses the same PCDB Table 4g fallback
+# (66% × 0.70 in-use factor) as the RdSAP-21 API path when no PCDF index is
+# lodged — the cascade handles a null index gracefully.
 _SAP_VENTILATION_TYPE_TO_MV_KIND: Final[Dict[int, Optional[str]]] = {
     1: None,                       # natural (with intermittent extract fans)
     2: None,                       # passive stack — treated as natural
@@ -83,8 +82,10 @@ _SAP_VENTILATION_TYPE_TO_MV_KIND: Final[Dict[int, Optional[str]]] = {
     4: "EXTRACT_OR_PIV_OUTSIDE",   # positive input from outside
     5: "EXTRACT_OR_PIV_OUTSIDE",   # mechanical extract, centralised (MEV c)
     6: "EXTRACT_OR_PIV_OUTSIDE",   # mechanical extract, decentralised (MEV dc)
-    7: None,                       # MVHR — deferred (efficiency not plumbed)
-    8: "MV",                       # balanced mechanical, no heat recovery
+    7: "MV",                       # balanced without heat recovery (MV)
+    8: "MVHR",                     # balanced with heat recovery (MVHR)
+    9: None,                       # natural with extract fans and/or passive vents (legacy)
+    10: None,                      # natural with extract fans and passive vents
 }
 # rdsap_uvalues WALL_CAVITY = 4 (D7 fallback; U comes from the description).
 _SAP_DEFAULT_WALL_CONSTRUCTION: Final[int] = 4
diff --git a/datatypes/epc/domain/tests/test_from_sap_schema.py b/datatypes/epc/domain/tests/test_from_sap_schema.py
index 28c86599..d4b3330b 100644
--- a/datatypes/epc/domain/tests/test_from_sap_schema.py
+++ b/datatypes/epc/domain/tests/test_from_sap_schema.py
@@ -410,6 +410,31 @@ class TestFromSapSchema17_1Ventilation:
         with pytest.raises(UnmappedApiCode):
             EpcPropertyDataMapper.from_sap_schema_17_1(schema)
 
+    @pytest.mark.parametrize("code", [9, 10])
+    def test_natural_ventilation_codes_9_and_10_map_to_none(self, code: int) -> None:
+        data = load("sap_17_1.json")
+        data["sap_ventilation"]["ventilation_type"] = code
+        schema = from_dict(SapSchema17_1, data)
+        result = EpcPropertyDataMapper.from_sap_schema_17_1(schema)
+        assert result.sap_ventilation is not None
+        assert result.sap_ventilation.mechanical_ventilation_kind is None
+
+    def test_ventilation_type_7_is_mv(self) -> None:
+        data = load("sap_17_1.json")
+        data["sap_ventilation"]["ventilation_type"] = 7
+        schema = from_dict(SapSchema17_1, data)
+        result = EpcPropertyDataMapper.from_sap_schema_17_1(schema)
+        assert result.sap_ventilation is not None
+        assert result.sap_ventilation.mechanical_ventilation_kind == "MV"
+
+    def test_ventilation_type_8_is_mvhr(self) -> None:
+        data = load("sap_17_1.json")
+        data["sap_ventilation"]["ventilation_type"] = 8
+        schema = from_dict(SapSchema17_1, data)
+        result = EpcPropertyDataMapper.from_sap_schema_17_1(schema)
+        assert result.sap_ventilation is not None
+        assert result.sap_ventilation.mechanical_ventilation_kind == "MVHR"
+
 
 class TestFromSapSchema17_1Heating:
     """Slice D6: full-SAP sap_heating (differing field names) maps onto the