diff --git a/src/EnergyPlus/HeatBalFiniteDiffManager.cc b/src/EnergyPlus/HeatBalFiniteDiffManager.cc
index febe9c5657d..c6987231e3b 100644
--- a/src/EnergyPlus/HeatBalFiniteDiffManager.cc
+++ b/src/EnergyPlus/HeatBalFiniteDiffManager.cc
@@ -2609,6 +2609,8 @@ namespace HeatBalFiniteDiffManager {
                 interNodeFlux - sourceFlux +
                 surfaceFD.CpDelXRhoS2(node) * (surfaceFD.TDT(node) - surfaceFD.TDpriortimestep(node)) / state.dataGlobal->TimeStepZoneSec;
         }
+        if (state.dataEnvrn->IsRain)
+            state.dataHeatBalSurf->SurfOpaqOutFaceCondFlux(Surf) = -surfaceFD.QDreport(1); // Update the outside flux if it is raining
     }
 
     void adjustPropertiesForPhaseChange(EnergyPlusData &state,
diff --git a/tst/EnergyPlus/unit/HeatBalFiniteDiffManager.unit.cc b/tst/EnergyPlus/unit/HeatBalFiniteDiffManager.unit.cc
index 8d2f9d02ee2..53e4fd2bc4c 100644
--- a/tst/EnergyPlus/unit/HeatBalFiniteDiffManager.unit.cc
+++ b/tst/EnergyPlus/unit/HeatBalFiniteDiffManager.unit.cc
@@ -53,6 +53,7 @@
 // EnergyPlus Headers
 #include <EnergyPlus/Construction.hh>
 #include <EnergyPlus/Data/EnergyPlusData.hh>
+#include <EnergyPlus/DataEnvironment.hh>
 #include <EnergyPlus/DataHeatBalSurface.hh>
 #include <EnergyPlus/HeatBalFiniteDiffManager.hh>
 #include <EnergyPlus/HeatBalanceManager.hh>
@@ -70,15 +71,18 @@ TEST_F(EnergyPlusFixture, HeatBalFiniteDiffManager_CalcNodeHeatFluxTest)
 {
     auto &SurfaceFD = state->dataHeatBalFiniteDiffMgr->SurfaceFD;
     int constexpr numNodes(4);
+    Real64 constexpr allowedTolerance = 0.0001;
     int nodeNum(0);
     SurfaceFD.allocate(1);
     int constexpr SurfNum(1);
-    SurfaceFD(SurfNum).QDreport.allocate(numNodes + 1);
-    SurfaceFD(SurfNum).TDpriortimestep.allocate(numNodes + 1);
-    SurfaceFD(SurfNum).TDT.allocate(numNodes + 1);
-    SurfaceFD(SurfNum).CpDelXRhoS1.allocate(numNodes + 1);
-    SurfaceFD(SurfNum).CpDelXRhoS2.allocate(numNodes + 1);
+    auto &surfFD = SurfaceFD(SurfNum);
+    surfFD.QDreport.allocate(numNodes + 1);
+    surfFD.TDpriortimestep.allocate(numNodes + 1);
+    surfFD.TDT.allocate(numNodes + 1);
+    surfFD.CpDelXRhoS1.allocate(numNodes + 1);
+    surfFD.CpDelXRhoS2.allocate(numNodes + 1);
     state->dataHeatBalSurf->SurfOpaqInsFaceCondFlux.allocate(1);
+    state->dataHeatBalSurf->SurfOpaqOutFaceCondFlux.allocate(1);
     state->dataGlobal->TimeStepZoneSec = 600.0;
 
     Real64 expectedResult1(0.0);
@@ -86,53 +90,71 @@ TEST_F(EnergyPlusFixture, HeatBalFiniteDiffManager_CalcNodeHeatFluxTest)
     Real64 expectedResult3(0.0);
     Real64 expectedResult4(0.0);
     Real64 expectedResult5(0.0);
+    Real64 expectedResultO(1.0);
 
     // Steady-state case
     state->dataHeatBalSurf->SurfOpaqInsFaceCondFlux(SurfNum) = 100.0;
     nodeNum = 1;
-    SurfaceFD(SurfNum).TDpriortimestep(nodeNum) = 20.0;
-    SurfaceFD(SurfNum).TDT(nodeNum) = 20.0;
-    SurfaceFD(SurfNum).CpDelXRhoS1(nodeNum) = 1000.0;
-    SurfaceFD(SurfNum).CpDelXRhoS2(nodeNum) = 2000.0;
+    surfFD.TDpriortimestep(nodeNum) = 20.0;
+    surfFD.TDT(nodeNum) = 20.0;
+    surfFD.CpDelXRhoS1(nodeNum) = 1000.0;
+    surfFD.CpDelXRhoS2(nodeNum) = 2000.0;
     expectedResult1 = state->dataHeatBalSurf->SurfOpaqInsFaceCondFlux(SurfNum);
 
     nodeNum = 2;
-    SurfaceFD(SurfNum).TDpriortimestep(nodeNum) = 22.0;
-    SurfaceFD(SurfNum).TDT(nodeNum) = 22.0;
-    SurfaceFD(SurfNum).CpDelXRhoS1(nodeNum) = 1000.0;
-    SurfaceFD(SurfNum).CpDelXRhoS2(nodeNum) = 2000.0;
+    surfFD.TDpriortimestep(nodeNum) = 22.0;
+    surfFD.TDT(nodeNum) = 22.0;
+    surfFD.CpDelXRhoS1(nodeNum) = 1000.0;
+    surfFD.CpDelXRhoS2(nodeNum) = 2000.0;
     expectedResult2 = state->dataHeatBalSurf->SurfOpaqInsFaceCondFlux(SurfNum);
 
     nodeNum = 3;
-    SurfaceFD(SurfNum).TDpriortimestep(nodeNum) = 23.0;
-    SurfaceFD(SurfNum).TDT(nodeNum) = 23.0;
-    SurfaceFD(SurfNum).CpDelXRhoS1(nodeNum) = 1000.0;
-    SurfaceFD(SurfNum).CpDelXRhoS2(nodeNum) = 2000.0;
+    surfFD.TDpriortimestep(nodeNum) = 23.0;
+    surfFD.TDT(nodeNum) = 23.0;
+    surfFD.CpDelXRhoS1(nodeNum) = 1000.0;
+    surfFD.CpDelXRhoS2(nodeNum) = 2000.0;
     expectedResult3 = state->dataHeatBalSurf->SurfOpaqInsFaceCondFlux(SurfNum);
 
     nodeNum = 4;
-    SurfaceFD(SurfNum).TDpriortimestep(nodeNum) = 26.0;
-    SurfaceFD(SurfNum).TDT(nodeNum) = 26.0;
-    SurfaceFD(SurfNum).CpDelXRhoS1(nodeNum) = 1000.0;
-    SurfaceFD(SurfNum).CpDelXRhoS2(nodeNum) = 2000.0;
+    surfFD.TDpriortimestep(nodeNum) = 26.0;
+    surfFD.TDT(nodeNum) = 26.0;
+    surfFD.CpDelXRhoS1(nodeNum) = 1000.0;
+    surfFD.CpDelXRhoS2(nodeNum) = 2000.0;
     expectedResult4 = state->dataHeatBalSurf->SurfOpaqInsFaceCondFlux(SurfNum);
 
     nodeNum = 5;
-    SurfaceFD(SurfNum).TDpriortimestep(nodeNum) = 27.0;
-    SurfaceFD(SurfNum).TDT(nodeNum) = 27.0;
-    SurfaceFD(SurfNum).CpDelXRhoS1(nodeNum) = 1000.0;
-    SurfaceFD(SurfNum).CpDelXRhoS2(nodeNum) = 2000.0;
+    surfFD.TDpriortimestep(nodeNum) = 27.0;
+    surfFD.TDT(nodeNum) = 27.0;
+    surfFD.CpDelXRhoS1(nodeNum) = 1000.0;
+    surfFD.CpDelXRhoS2(nodeNum) = 2000.0;
     expectedResult5 = state->dataHeatBalSurf->SurfOpaqInsFaceCondFlux(SurfNum);
 
+    state->dataEnvrn->IsRain = false;
+    state->dataHeatBalSurf->SurfOpaqOutFaceCondFlux(SurfNum) = 77.0;
+    expectedResultO = 77.0;
+
+    CalcNodeHeatFlux(*state, SurfNum, numNodes);
+    EXPECT_NEAR(surfFD.QDreport(1), expectedResult1, allowedTolerance);
+    EXPECT_NEAR(surfFD.QDreport(2), expectedResult2, allowedTolerance);
+    EXPECT_NEAR(surfFD.QDreport(3), expectedResult3, allowedTolerance);
+    EXPECT_NEAR(surfFD.QDreport(4), expectedResult4, allowedTolerance);
+    EXPECT_NEAR(surfFD.QDreport(5), expectedResult5, allowedTolerance);
+    EXPECT_NEAR(state->dataHeatBalSurf->SurfOpaqOutFaceCondFlux(SurfNum), expectedResultO, allowedTolerance);
+
+    state->dataEnvrn->IsRain = true;
+    state->dataHeatBalSurf->SurfOpaqOutFaceCondFlux(SurfNum) = 77.0;
+    expectedResultO = -state->dataHeatBalSurf->SurfOpaqInsFaceCondFlux(SurfNum);
+
     CalcNodeHeatFlux(*state, SurfNum, numNodes);
-    EXPECT_NEAR(SurfaceFD(SurfNum).QDreport(1), expectedResult1, 0.0001);
-    EXPECT_NEAR(SurfaceFD(SurfNum).QDreport(2), expectedResult2, 0.0001);
-    EXPECT_NEAR(SurfaceFD(SurfNum).QDreport(3), expectedResult3, 0.0001);
-    EXPECT_NEAR(SurfaceFD(SurfNum).QDreport(4), expectedResult4, 0.0001);
-    EXPECT_NEAR(SurfaceFD(SurfNum).QDreport(5), expectedResult5, 0.0001);
+    EXPECT_NEAR(surfFD.QDreport(1), expectedResult1, allowedTolerance);
+    EXPECT_NEAR(surfFD.QDreport(2), expectedResult2, allowedTolerance);
+    EXPECT_NEAR(surfFD.QDreport(3), expectedResult3, allowedTolerance);
+    EXPECT_NEAR(surfFD.QDreport(4), expectedResult4, allowedTolerance);
+    EXPECT_NEAR(surfFD.QDreport(5), expectedResult5, allowedTolerance);
+    EXPECT_NEAR(state->dataHeatBalSurf->SurfOpaqOutFaceCondFlux(SurfNum), expectedResultO, allowedTolerance);
 
     // Reset
-    SurfaceFD(SurfNum).QDreport = 0.0;
+    surfFD.QDreport = 0.0;
     expectedResult1 = 0.0;
     expectedResult2 = 0.0;
     expectedResult3 = 0.0;
@@ -144,50 +166,67 @@ TEST_F(EnergyPlusFixture, HeatBalFiniteDiffManager_CalcNodeHeatFluxTest)
     state->dataHeatBalSurf->SurfOpaqInsFaceCondFlux(SurfNum) = -200.0;
 
     nodeNum = 5;
-    SurfaceFD(SurfNum).TDpriortimestep(nodeNum) = 27.5;
-    SurfaceFD(SurfNum).TDT(nodeNum) = 27.0;
-    SurfaceFD(SurfNum).CpDelXRhoS1(nodeNum) = 0.0;
-    SurfaceFD(SurfNum).CpDelXRhoS2(nodeNum) = 0.0;
+    surfFD.TDpriortimestep(nodeNum) = 27.5;
+    surfFD.TDT(nodeNum) = 27.0;
+    surfFD.CpDelXRhoS1(nodeNum) = 0.0;
+    surfFD.CpDelXRhoS2(nodeNum) = 0.0;
     expectedResult5 = state->dataHeatBalSurf->SurfOpaqInsFaceCondFlux(SurfNum);
 
     nodeNum = 4;
-    SurfaceFD(SurfNum).TDpriortimestep(nodeNum) = 26.0;
-    SurfaceFD(SurfNum).TDT(nodeNum) = 26.0;
-    SurfaceFD(SurfNum).CpDelXRhoS1(nodeNum) = 0.0;
-    SurfaceFD(SurfNum).CpDelXRhoS2(nodeNum) = 2000.0;
+    surfFD.TDpriortimestep(nodeNum) = 26.0;
+    surfFD.TDT(nodeNum) = 26.0;
+    surfFD.CpDelXRhoS1(nodeNum) = 0.0;
+    surfFD.CpDelXRhoS2(nodeNum) = 2000.0;
     expectedResult4 = expectedResult5; // r-layer with zero heat capacity, so flux passes through
 
     nodeNum = 3;
-    SurfaceFD(SurfNum).TDpriortimestep(nodeNum) = 23.0;
-    SurfaceFD(SurfNum).TDT(nodeNum) = 23.0;
-    SurfaceFD(SurfNum).CpDelXRhoS1(nodeNum) = 1000.0;
-    SurfaceFD(SurfNum).CpDelXRhoS2(nodeNum) = 2000.0;
+    surfFD.TDpriortimestep(nodeNum) = 23.0;
+    surfFD.TDT(nodeNum) = 23.0;
+    surfFD.CpDelXRhoS1(nodeNum) = 1000.0;
+    surfFD.CpDelXRhoS2(nodeNum) = 2000.0;
     expectedResult3 = expectedResult4; // no change in temperature at nodes 4 and 3, so flux passes through
 
     nodeNum = 2;
-    SurfaceFD(SurfNum).TDpriortimestep(nodeNum) = 22.2;
-    SurfaceFD(SurfNum).TDT(nodeNum) = 22.0;
-    SurfaceFD(SurfNum).CpDelXRhoS1(nodeNum) = 1000.0;
-    SurfaceFD(SurfNum).CpDelXRhoS2(nodeNum) = 2000.0;
-    expectedResult2 = expectedResult3 + (SurfaceFD(SurfNum).TDT(nodeNum) - SurfaceFD(SurfNum).TDpriortimestep(nodeNum)) *
-                                            SurfaceFD(SurfNum).CpDelXRhoS2(nodeNum) / state->dataGlobal->TimeStepZoneSec;
+    surfFD.TDpriortimestep(nodeNum) = 22.2;
+    surfFD.TDT(nodeNum) = 22.0;
+    surfFD.CpDelXRhoS1(nodeNum) = 1000.0;
+    surfFD.CpDelXRhoS2(nodeNum) = 2000.0;
+    expectedResult2 =
+        expectedResult3 + (surfFD.TDT(nodeNum) - surfFD.TDpriortimestep(nodeNum)) * surfFD.CpDelXRhoS2(nodeNum) / state->dataGlobal->TimeStepZoneSec;
 
     nodeNum = 1;
-    SurfaceFD(SurfNum).TDpriortimestep(nodeNum) = 20.1;
-    SurfaceFD(SurfNum).TDT(nodeNum) = 20.0;
-    SurfaceFD(SurfNum).CpDelXRhoS1(nodeNum) = 1000.0;
-    SurfaceFD(SurfNum).CpDelXRhoS2(nodeNum) = 2000.0;
-    expectedResult1 = expectedResult2 + (SurfaceFD(SurfNum).TDT(nodeNum + 1) - SurfaceFD(SurfNum).TDpriortimestep(nodeNum + 1)) *
-                                            SurfaceFD(SurfNum).CpDelXRhoS1(nodeNum + 1) / state->dataGlobal->TimeStepZoneSec;
-    expectedResult1 = expectedResult1 + (SurfaceFD(SurfNum).TDT(nodeNum) - SurfaceFD(SurfNum).TDpriortimestep(nodeNum)) *
-                                            SurfaceFD(SurfNum).CpDelXRhoS2(nodeNum) / state->dataGlobal->TimeStepZoneSec;
+    surfFD.TDpriortimestep(nodeNum) = 20.1;
+    surfFD.TDT(nodeNum) = 20.0;
+    surfFD.CpDelXRhoS1(nodeNum) = 1000.0;
+    surfFD.CpDelXRhoS2(nodeNum) = 2000.0;
+    expectedResult1 = expectedResult2 + (surfFD.TDT(nodeNum + 1) - surfFD.TDpriortimestep(nodeNum + 1)) * surfFD.CpDelXRhoS1(nodeNum + 1) /
+                                            state->dataGlobal->TimeStepZoneSec;
+    expectedResult1 =
+        expectedResult1 + (surfFD.TDT(nodeNum) - surfFD.TDpriortimestep(nodeNum)) * surfFD.CpDelXRhoS2(nodeNum) / state->dataGlobal->TimeStepZoneSec;
+
+    state->dataEnvrn->IsRain = false;
+    state->dataHeatBalSurf->SurfOpaqOutFaceCondFlux(SurfNum) = 123.0;
+    expectedResultO = 123.0;
+
+    CalcNodeHeatFlux(*state, SurfNum, numNodes);
+    EXPECT_NEAR(surfFD.QDreport(1), expectedResult1, allowedTolerance);
+    EXPECT_NEAR(surfFD.QDreport(2), expectedResult2, allowedTolerance);
+    EXPECT_NEAR(surfFD.QDreport(3), expectedResult3, allowedTolerance);
+    EXPECT_NEAR(surfFD.QDreport(4), expectedResult4, allowedTolerance);
+    EXPECT_NEAR(surfFD.QDreport(5), expectedResult5, allowedTolerance);
+    EXPECT_NEAR(state->dataHeatBalSurf->SurfOpaqOutFaceCondFlux(SurfNum), expectedResultO, allowedTolerance);
+
+    state->dataEnvrn->IsRain = true;
+    state->dataHeatBalSurf->SurfOpaqOutFaceCondFlux(SurfNum) = 123.0;
+    expectedResultO = -expectedResult1;
 
     CalcNodeHeatFlux(*state, SurfNum, numNodes);
-    EXPECT_NEAR(SurfaceFD(SurfNum).QDreport(1), expectedResult1, 0.0001);
-    EXPECT_NEAR(SurfaceFD(SurfNum).QDreport(2), expectedResult2, 0.0001);
-    EXPECT_NEAR(SurfaceFD(SurfNum).QDreport(3), expectedResult3, 0.0001);
-    EXPECT_NEAR(SurfaceFD(SurfNum).QDreport(4), expectedResult4, 0.0001);
-    EXPECT_NEAR(SurfaceFD(SurfNum).QDreport(5), expectedResult5, 0.0001);
+    EXPECT_NEAR(surfFD.QDreport(1), expectedResult1, allowedTolerance);
+    EXPECT_NEAR(surfFD.QDreport(2), expectedResult2, allowedTolerance);
+    EXPECT_NEAR(surfFD.QDreport(3), expectedResult3, allowedTolerance);
+    EXPECT_NEAR(surfFD.QDreport(4), expectedResult4, allowedTolerance);
+    EXPECT_NEAR(surfFD.QDreport(5), expectedResult5, allowedTolerance);
+    EXPECT_NEAR(state->dataHeatBalSurf->SurfOpaqOutFaceCondFlux(SurfNum), expectedResultO, allowedTolerance);
 }
 
 TEST_F(EnergyPlusFixture, HeatBalFiniteDiffManager_adjustPropertiesForPhaseChange)