diff --git a/Source/hvac.f90 b/Source/hvac.f90
index 257fdb49e1e..a3e57c05bc8 100644
--- a/Source/hvac.f90
+++ b/Source/hvac.f90
@@ -1875,13 +1875,28 @@ SUBROUTINE DPSTARCALC
       IF (IPZ==IOPZ) CYCLE
       IF (CONNECTED_ZONES(IPZ,IOPZ,1)) PSUM_TOT(IPZ) = PSUM_TOT(IPZ) + PSUM(IOPZ,1)
    ENDDO
+ENDDO
+
+DO IPZ = 1,N_ZONE
+   PZ => P_ZONE(IPZ)
+   IF (PZ%N_DUCTNODES==0) CYCLE
    DO NN = 1,PZ%N_DUCTNODES
       DN=>DUCTNODE(PZ%NODE_INDEX(NN))
       DU=>DUCT(DN%DUCT_INDEX(1))
       DPSTAR(IPZ) = DPSTAR(IPZ)  - DN%DIR(1) * DU%AREA * DU%VEL(OLD) * DT_HV/PSUM_TOT(IPZ)
       IF (DU%FIXED) DPSTAR(IPZ) = DPSTAR(IPZ)  + DN%DIR(1) * DU%AREA * DU%VEL(NEW) * DT_HV/PSUM_TOT(IPZ)
+      DO IOPZ = 1, N_ZONE
+         IF (IPZ==IOPZ) CYCLE
+         IF (P_ZONE(IOPZ)%N_DUCTNODES==0) CYCLE
+         IF (CONNECTED_ZONES(IPZ,IOPZ,1)) THEN
+            IF (P_ZONE(IPOZ)%N_DUCTNODES==0) CYCLE
+            DPSTAR(IOPZ) = DPSTAR(IOPZ)  - DN%DIR(1) * DU%AREA * DU%VEL(OLD) * DT_HV/PSUM_TOT(IPZ)
+            IF (DU%FIXED) DPSTAR(IOPZ) = DPSTAR(IOPZ)  + DN%DIR(1) * DU%AREA * DU%VEL(NEW) * DT_HV/PSUM_TOT(IPZ)
+         ENDIF
+      ENDDO
    ENDDO
 ENDDO
+
 END SUBROUTINE DPSTARCALC
 
 !> \brief Builds the right hand side of the HVAC flow matrix for momentum conservation in a duct