Merge pull request #1405 from Hestia-Homes/fix/1376-offpeak-underfloor

Score off-peak electric underfloor on its own codes, not direct-acting single-meter (#1376)

docs/adr/0046-electric-underfloor-scored-by-its-own-codes-meter-deferred-when-tariff-ambiguous.md

@@ -0,0 +1,92 @@
+# Electric underfloor is scored by its own SAP codes; the meter defers to the cert when the tariff is ambiguous
+
+## Status
+
+accepted
+
+## Context
+
+Electric-underfloor `main_heating_system` overrides had no archetype, so the LLM
+classifier funnelled them into the nearest wrong bucket (#1376):
+
+| description | rows | mis-mapped to |
+| --- | --- | --- |
+| Electric Underfloor Heating: In concrete slab (off-peak only) | 15 | Direct-acting electric (191), **Single** meter |
+| Electric Underfloor Heating: In screed above insulation (standard or off peak) | 63 | Direct-acting electric (191), **Single** meter |
+| Electric Underfloor Heating: Integrated (storage+direct-acting) (off peak) | 12 | Electric storage heaters, old (401) |
+
+The **meter is the crux**. A Landlord heating override drags an assumed meter from
+its SAP code (ADR-0035), and the `keep_existing_off_peak_meter` mitigation
+([overlay_applicator.py](../../domain/modelling/scoring/overlay_applicator.py))
+protects a cert's lodged off-peak meter — but *only when the overlay's own desired
+meter is off-peak*. Direct-acting (191) is a **Single**-meter system, so the
+mitigation never fires and the overlay **forces Single**, overwriting the cert's
+meter. For off-peak underfloor that bills overnight heat at the peak rate and
+craters SAP — the exact Class-A meter defect.
+
+SAP Table 4a has **dedicated electric-underfloor codes** (labels from
+`cert_to_inputs.py`): **421** in concrete slab (off-peak only), **422** integrated
+(storage+direct-acting), **424** in screed above insulation (423 integrated-low-
+off-peak and 425 timber-floor are not in the corpus). Per SAP 10.2 §12, **421/422
+are off-peak (Rule 2, 7-hour → Dual)**; **424 is not off-peak-implying (Single)**.
+
+A lodged-meter audit is decisive for the screed case: **51 of 63 (81%)** of the
+`"…in screed (standard or off peak)"` dwellings lodge an **off-peak** meter (24-hour
+dual or 7/10-hour), the rest single. The description itself says "standard **or**
+off peak" — so the archetype genuinely cannot know the tariff; the cert does.
+Forcing 424/Single would downgrade 81%; forcing Dual would over-credit the ~19% on
+single.
+
+## Decision
+
+Add three electric-underfloor archetypes mapping to their own SAP codes, and treat
+the meter per what the description actually asserts.
+
+1. **New archetypes** in `_MAIN_HEATING_CODES`:
+   `"Electric underfloor, in concrete slab (off-peak)"` → **421**,
+   `"Electric underfloor, integrated storage and direct-acting"` → **422**,
+   `"Electric underfloor, in screed above insulation"` → **424**.
+2. **Electricity fuel (29)** drags for 421/422/424 via `_natural_fuel_for` — electric
+   underfloor is unambiguously electric (ADR-0041), closing the prior no-fuel gap.
+3. **421 and 422 assert an off-peak Dual meter.** Their descriptions positively
+   claim off-peak ("off-peak only" / "off peak"), and both are already in
+   `_ASSUMED_DUAL_METER_CODES`; the `keep_existing_off_peak_meter` mitigation keeps
+   a more-specific cert off-peak meter and applies Dual to a single-rate cert.
+4. **424 (screed) defers the meter to the cert.** Because "standard or off peak" is
+   tariff-agnostic and 81% lodge off-peak, `_meter_for` returns **`None`** for 424
+   (a new meter-agnostic set), so the overlay leaves `meter_type` unset and the
+   lodged meter stands — each dwelling scores on its actual tariff. This is a
+   **targeted exception to the "always set the meter, never let it bleed"
+   invariant**: that invariant guards against a switched-*off* storage system
+   leaving a stale Dual meter, but an underfloor override *confirms* underfloor —
+   there is no switch-off, so deferring is faithful, not a bleed.
+5. **Deterministic `main_heating_guard` + reclassify** (TEXT-first, pgEnum-deferred),
+   reusing the generalized `reclassify_main_heating.py`. All three underfloor
+   descriptions are description-determined, so the guard resolves them directly (no
+   fuel-awareness needed) and the reclassify follows.
+
+## Consequences
+
+- The 15 concrete-slab-off-peak rows stop being billed at the peak rate (191/Single
+  → 421/Dual); the 12 integrated rows get the correct underfloor code (401 → 422,
+  meter already Dual); the 63 screed rows keep their lodged (81% off-peak) meter and
+  score on code 424 with correct screed responsiveness (Table 4d R=0.75). Correct
+  Rebaselining (ADR-0039).
+- **FE-owned pgEnum additions (Dan):** three new `main_heating_system` values —
+  `"Electric underfloor, in concrete slab (off-peak)"`, `"Electric underfloor,
+  integrated storage and direct-acting"`, `"Electric underfloor, in screed above
+  insulation"`. TEXT read path fixed on merge; cache writes defer to the migration.
+- `_meter_for` becomes `Optional[str]` (a code may defer the meter). Every existing
+  code keeps its current Single/Dual answer; only 424 returns `None`.
+- Extends [ADR-0041](0041-landlord-heating-classification-targets-a-complete-modellable-taxonomy.md)
+  and [ADR-0035](0035-coherent-heating-system-synthesis.md); refines the
+  `keep_existing_off_peak_meter` behaviour ADR-0035 introduced.
+
+### Alternatives rejected
+
+- **Force Single (424 per spec).** Rejected: downgrades the 81% lodged off-peak,
+  reproducing the meter bug.
+- **Force Dual for screed.** Rejected: over-credits the ~19% genuinely on single and
+  asserts a tariff the "standard or off peak" description does not claim.
+- **Map underfloor to Direct-acting (191) / old storage (401) as today.** Rejected:
+  wrong code (responsiveness/meter) and the source of the mis-score.

domain/epc/property_overlays/main_heating_system_overlay.py

@@ -45,6 +45,10 @@ _OFF_PEAK_METER = "Dual"
 # meter bleed through and bill the new gas/direct-acting system on an Economy-7
 # split (the mirror of the storage→Dual drag, ADR-0035).
 _SINGLE_RATE_METER = "Single"
+# Meter-agnostic codes: the archetype cannot determine the tariff, so the overlay
+# defers `meter_type` to the cert (`_meter_for` → None). Screed underfloor (424) is
+# "standard or off peak" — 81% of the corpus lodge off-peak (ADR-0046).
+_METER_AGNOSTIC_CODES = frozenset({424})
 
 # Electric room heaters (SAP Table 4a 691). They don't *require* off-peak the way
 # storage/CPSU do, so they're absent from the calculator's §12
@@ -116,6 +120,9 @@ _ELECTRIC_ROOM_HEATER_CODES = frozenset(range(691, 702))
 # unambiguously electric, so they drag electricity like the electric room heaters
 # (ADR-0045, closing the prior no-fuel gap on 191/192).
 _ELECTRIC_BOILER_CODES = frozenset({191, 192})
+# Electric underfloor — SAP Table 4a 421/422 (off-peak) and 424 (screed) — also
+# unambiguously electric (ADR-0046).
+_ELECTRIC_UNDERFLOOR_CODES = frozenset({421, 422, 424})
 
 # Heat pumps (SAP Table 4a 211-224 wet, 521-527 warm-air) are category 4 and
 # unambiguously electric (natural fuel 29). Modellable on the default code's SPF
@@ -184,6 +191,13 @@ _MAIN_HEATING_CODES: dict[str, int] = {
     # Electric CPSU — SAP Table 4a 192. Electric (drags 29), on an off-peak Dual
     # meter (already in _ASSUMED_DUAL_METER_CODES; §12 Rule 1 10-hour) — ADR-0045.
     "Electric CPSU": 192,
+    # Electric underfloor — dedicated SAP Table 4a codes, all electric (drag 29).
+    # 421 concrete slab / 422 integrated are off-peak (Dual, §12 Rule 2); 424
+    # screed is tariff-ambiguous ("standard or off peak") so it DEFERS the meter to
+    # the cert (ADR-0046).
+    "Electric underfloor, in concrete slab (off-peak)": 421,
+    "Electric underfloor, integrated storage and direct-acting": 422,
+    "Electric underfloor, in screed above insulation": 424,
     "Electric room heaters": 691,
     "Solid fuel room heater, closed": 633,
     # Solid-fuel room heaters off the Gas CPSU dumping ground (ADR-0045). SAP
@@ -218,11 +232,19 @@ _MAIN_HEATING_CODES: dict[str, int] = {
 }
 
 
-def _meter_for(code: int) -> str:
+def _meter_for(code: int) -> Optional[str]:
     """The coherent meter a heating code implies: an off-peak ("Dual") meter for
     the §12 off-peak systems and all-electric room-heater dwellings
     (`_ASSUMED_DUAL_METER_CODES`), an explicit single-rate ("Single") meter for
-    every other system. Always set — never left to bleed."""
+    every other system — set explicitly so it never bleeds.
+
+    Exception: a **meter-agnostic** code (`_METER_AGNOSTIC_CODES` — screed
+    underfloor 424, "standard or off peak") returns ``None`` so the overlay leaves
+    `meter_type` unset and the cert's lodged tariff stands. The archetype genuinely
+    cannot know the tariff, and unlike a switched-off storage system it is not a
+    re-metering, so deferring is faithful, not a bleed (ADR-0046)."""
+    if code in _METER_AGNOSTIC_CODES:
+        return None
     return _OFF_PEAK_METER if code in _ASSUMED_DUAL_METER_CODES else _SINGLE_RATE_METER
 
 
@@ -264,6 +286,7 @@ def _natural_fuel_for(code: int) -> Optional[int]:
         or code in _HEAT_PUMP_CODES
         or code == _HHR_STORAGE_CODE
         or code in _ELECTRIC_BOILER_CODES
+        or code in _ELECTRIC_UNDERFLOOR_CODES
     ):
         return _ELECTRICITY_FUEL
     if code in _SOLID_FUEL_ROOM_HEATER_CODES:

domain/epc/property_overrides/main_heating_guard.py

@@ -20,6 +20,10 @@ def main_heating_guard(description: str) -> Optional[MainHeatingSystemType]:
       solid-fuel room heaters (open fire 631 / + back boiler 632 / closed + boiler
       634) and electric ``"NA"``-type boilers (SAP 191). "NA" is the boiler-type
       value meaning "not a gas combi/regular/CPSU", i.e. an electric boiler.
+    - **Electric underfloor** (ADR-0046): dumped into Direct-acting (191) / old
+      storage (401) for want of the dedicated SAP underfloor codes — in concrete
+      slab (421, off-peak), integrated storage+direct-acting (422), in screed (424,
+      meter deferred to the cert).
 
     Returns ``None`` for descriptions the LLM already classifies correctly (genuine
     gas boilers, other storage subtypes, a plain closed room heater) and for varied
@@ -30,6 +34,14 @@ def main_heating_guard(description: str) -> Optional[MainHeatingSystemType]:
     text = description.lower()
     if "high heat retention" in text:
         return MainHeatingSystemType.ELECTRIC_STORAGE_HIGH_HEAT_RETENTION
+    if "underfloor" in text:
+        if "concrete slab" in text:
+            return MainHeatingSystemType.ELECTRIC_UNDERFLOOR_SLAB_OFF_PEAK
+        if "integrated" in text:
+            return MainHeatingSystemType.ELECTRIC_UNDERFLOOR_INTEGRATED
+        if "screed" in text:
+            return MainHeatingSystemType.ELECTRIC_UNDERFLOOR_SCREED
+        return None
     if "rated na" in text:
         return MainHeatingSystemType.ELECTRIC_BOILER
     if "open fire" in text and "back boiler" in text:

domain/epc/property_overrides/main_heating_system_type.py

@@ -29,6 +29,13 @@ class MainHeatingSystemType(Enum):
     DIRECT_ELECTRIC = "Direct-acting electric"
     ELECTRIC_BOILER = "Electric boiler"
     ELECTRIC_CPSU = "Electric CPSU"
+    ELECTRIC_UNDERFLOOR_SLAB_OFF_PEAK = (
+        "Electric underfloor, in concrete slab (off-peak)"
+    )
+    ELECTRIC_UNDERFLOOR_INTEGRATED = (
+        "Electric underfloor, integrated storage and direct-acting"
+    )
+    ELECTRIC_UNDERFLOOR_SCREED = "Electric underfloor, in screed above insulation"
     ELECTRIC_ROOM_HEATERS = "Electric room heaters"
     SOLID_FUEL_ROOM_HEATER_CLOSED = "Solid fuel room heater, closed"
     SOLID_FUEL_ROOM_HEATER_OPEN_FIRE = "Solid fuel room heater, open fire"

scripts/reclassify_main_heating.py

@@ -1,11 +1,13 @@
 """One-time re-classification of main-heating overrides funnelled into a garbage
 drawer for want of a correct archetype (#1376).
 
-Covers both dumping grounds the ``main_heating_guard`` now rescues:
+Covers the dumping grounds the ``main_heating_guard`` now rescues:
 - **HHRSH** (ADR-0044): "High heat retention storage heaters" → "Electric storage
   heaters, old" (SAP 401), the worst old type — 111 rows.
 - **Gas CPSU** (ADR-0045): solid-fuel room heaters (open fire / + back boiler /
   closed + boiler) and electric "NA"-type boilers → "Gas CPSU" (120, mains gas).
+- **Electric underfloor** (ADR-0046): concrete slab (421) / integrated (422) /
+  screed (424) dumped into Direct-acting (191) / old storage (401).
 
 The live classifier now applies ``main_heating_guard`` deterministically (so new
 intakes are correct); this fixes the rows written before it. The **same guard**

tests/domain/epc/test_main_heating_guard.py

@@ -19,6 +19,34 @@ def test_guard_resolves_high_heat_retention_storage() -> None:
     assert result is MainHeatingSystemType.ELECTRIC_STORAGE_HIGH_HEAT_RETENTION
 
 
+@pytest.mark.parametrize(
+    ("description", "expected"),
+    [
+        # Electric underfloor dumped into Direct-acting / old storage (ADR-0046).
+        (
+            "Electric Underfloor Heating: In concrete slab (off-peak only)",
+            MainHeatingSystemType.ELECTRIC_UNDERFLOOR_SLAB_OFF_PEAK,
+        ),
+        (
+            "Electric Underfloor Heating: Integrated (storage+direct-acting) (off peak)",
+            MainHeatingSystemType.ELECTRIC_UNDERFLOOR_INTEGRATED,
+        ),
+        (
+            "Electric Underfloor Heating: In screed above insulation (standard or off peak)",
+            MainHeatingSystemType.ELECTRIC_UNDERFLOOR_SCREED,
+        ),
+    ],
+)
+def test_guard_resolves_electric_underfloor(
+    description: str, expected: MainHeatingSystemType
+) -> None:
+    # Act
+    result = main_heating_guard(description)
+
+    # Assert
+    assert result is expected
+
+
 @pytest.mark.parametrize(
     ("description", "expected"),
     [

tests/domain/epc/test_main_heating_system_overlay.py

@@ -13,6 +13,7 @@ from domain.epc.property_overlays.main_fuel_overlay import fuel_overlay_for
 from domain.epc.property_overlays.main_heating_system_overlay import (
     _ASSUMED_DUAL_METER_CODES,
     _MAIN_HEATING_CODES,
+    _METER_AGNOSTIC_CODES,
     main_heating_overlay_for,
 )
 from domain.epc.property_overlays.water_heating_overlay import (
@@ -127,6 +128,60 @@ def test_electric_cpsu_decodes_to_192_electric_on_an_off_peak_meter() -> None:
     assert simulation.heating.meter_type == "Dual"
 
 
+@pytest.mark.parametrize(
+    ("main_heating_value", "code"),
+    [
+        # Electric underfloor funnelled into Direct-acting (191) / old storage (401)
+        # for want of the dedicated SAP Table 4a underfloor codes (ADR-0046).
+        ("Electric underfloor, in concrete slab (off-peak)", 421),
+        ("Electric underfloor, integrated storage and direct-acting", 422),
+        ("Electric underfloor, in screed above insulation", 424),
+    ],
+)
+def test_electric_underfloor_decodes_to_its_own_code_dragging_electricity(
+    main_heating_value: str, code: int
+) -> None:
+    # Act
+    simulation = main_heating_overlay_for(main_heating_value, 0)
+
+    # Assert — its own underfloor code, electric (29).
+    assert simulation is not None
+    assert simulation.heating is not None
+    assert simulation.heating.sap_main_heating_code == code
+    assert simulation.heating.main_fuel_type == 29
+
+
+@pytest.mark.parametrize(
+    "main_heating_value",
+    [
+        # "off-peak only" / "off peak" positively claim off-peak.
+        "Electric underfloor, in concrete slab (off-peak)",
+        "Electric underfloor, integrated storage and direct-acting",
+    ],
+)
+def test_off_peak_underfloor_asserts_a_dual_meter(main_heating_value: str) -> None:
+    # Act
+    simulation = main_heating_overlay_for(main_heating_value, 0)
+
+    # Assert — an off-peak underfloor must not bill overnight heat at the peak rate.
+    assert simulation is not None
+    assert simulation.heating is not None
+    assert simulation.heating.meter_type == "Dual"
+
+
+def test_screed_underfloor_defers_the_meter_to_the_cert() -> None:
+    # "In screed above insulation (standard or off peak)" is tariff-ambiguous (81%
+    # of the corpus lodge off-peak), so the archetype cannot know the meter — it
+    # leaves meter_type unset so the cert's lodged meter stands (ADR-0046).
+    simulation = main_heating_overlay_for(
+        "Electric underfloor, in screed above insulation", 0
+    )
+
+    assert simulation is not None
+    assert simulation.heating is not None
+    assert simulation.heating.meter_type is None
+
+
 @pytest.mark.parametrize(
     ("main_heating_value", "code"),
     [
@@ -313,11 +368,18 @@ def test_off_peak_archetypes_drag_dual_others_drag_single() -> None:
     # the calculator's single off-peak classification, so any archetype whose
     # code implies off-peak MUST synthesise a Dual meter and every other code
     # MUST synthesise a Single meter — a system switch can never silently leave
-    # the previous system's meter in place.
+    # the previous system's meter in place. The one exception is a meter-agnostic
+    # code (screed underfloor, tariff-ambiguous), which defers to the cert's
+    # lodged meter (None) rather than assert one (ADR-0046).
     for value, code in _MAIN_HEATING_CODES.items():
         simulation = main_heating_overlay_for(value, 0)
         assert simulation is not None and simulation.heating is not None
-        expected = "Dual" if code in _ASSUMED_DUAL_METER_CODES else "Single"
+        if code in _METER_AGNOSTIC_CODES:
+            expected = None
+        elif code in _ASSUMED_DUAL_METER_CODES:
+            expected = "Dual"
+        else:
+            expected = "Single"
         assert simulation.heating.meter_type == expected, value
 
 

tests/scripts/test_reclassify_main_heating.py

@@ -65,12 +65,50 @@ def test_garbage_drawer_rows_are_remapped_to_faithful_archetypes() -> None:
     }
 
 
+def test_electric_underfloor_rows_are_remapped_off_direct_acting_and_old_storage() -> None:
+    # Underfloor dumped into Direct-acting (191) / old storage (401) → its own codes
+    # (ADR-0046). Description-determined, so the guard-based reclassify handles it.
+    stored = [
+        (
+            "electric underfloor heating: in concrete slab (off-peak only)",
+            "Direct-acting electric",
+        ),
+        (
+            "electric underfloor heating: integrated (storage+direct-acting) (off peak)",
+            "Electric storage heaters, old",
+        ),
+        (
+            "electric underfloor heating: in screed above insulation (standard or off peak)",
+            "Direct-acting electric",
+        ),
+    ]
+
+    # Act
+    corrections = main_heating_corrections(stored)
+
+    # Assert
+    assert corrections == {
+        "electric underfloor heating: in concrete slab (off-peak only)": (
+            "Electric underfloor, in concrete slab (off-peak)"
+        ),
+        "electric underfloor heating: integrated (storage+direct-acting) (off peak)": (
+            "Electric underfloor, integrated storage and direct-acting"
+        ),
+        "electric underfloor heating: in screed above insulation (standard or off peak)": (
+            "Electric underfloor, in screed above insulation"
+        ),
+    }
+
+
 def test_every_guard_target_round_trips_to_a_resolvable_archetype() -> None:
     # Every archetype the guard emits for the rescued descriptions must decode to a
     # real SAP heating code — a guard/overlay drift can't silently write an
-    # unmodellable value (ADR-0044, ADR-0045).
+    # unmodellable value (ADR-0044, ADR-0045, ADR-0046).
     descriptions = [
         "Electric Storage Systems: High heat retention storage heaters",
+        "Electric Underfloor Heating: In concrete slab (off-peak only)",
+        "Electric Underfloor Heating: Integrated (storage+direct-acting) (off peak)",
+        "Electric Underfloor Heating: In screed above insulation (standard or off peak)",
         "Solid fuel room heaters: Open fire in grate",
         "Solid fuel room heaters: Open fire with back boiler (no radiators)",
         "Solid fuel room heaters: Closed room heater with boiler (no radiators)",