diff --git a/Source/cons.f90 b/Source/cons.f90
index 178c412acb2..a57a166052c 100644
--- a/Source/cons.f90
+++ b/Source/cons.f90
@@ -633,8 +633,7 @@ MODULE GLOBAL_CONSTANTS
 ! Number of initial value, pressure zone, and multiplier derived types
 
 INTEGER :: N_INIT,N_ZONE,N_MULT,N_MOVE
-LOGICAL, ALLOCATABLE, DIMENSION(:,:) :: CONNECTED_ZONES
-INTEGER, ALLOCATABLE, DIMENSION(:,:) :: CONNECTED_ZONES_LOC
+INTEGER, ALLOCATABLE, DIMENSION(:,:) :: CONNECTED_ZONES
 REAL(EB) :: MINIMUM_ZONE_VOLUME=0._EB
 REAL(EB) :: PRESSURE_RELAX_TIME=1._EB
 
diff --git a/Source/divg.f90 b/Source/divg.f90
index c2ed9e4d16e..be1160bc814 100644
--- a/Source/divg.f90
+++ b/Source/divg.f90
@@ -1114,15 +1114,15 @@ SUBROUTINE MERGE_PRESSURE_ZONES
    IPZ  = PRESSURE_ZONE(BC%IIG,BC%JJG,BC%KKG)
    IOPZ = PRESSURE_ZONE(BC%II,BC%JJ,BC%KK)
    IF (IW>N_EXTERNAL_WALL_CELLS .AND. IPZ/=IOPZ) THEN
-      CONNECTED_ZONES(IOPZ,IPZ) = .TRUE.
-      CONNECTED_ZONES(IPZ,IOPZ) = .TRUE.
+      CONNECTED_ZONES(IOPZ,IPZ) = 1
+      CONNECTED_ZONES(IPZ,IOPZ) = 1
    ENDIF
    IF (WC%BOUNDARY_TYPE==OPEN_BOUNDARY) THEN
-      CONNECTED_ZONES(0,IPZ) = .TRUE.
-      CONNECTED_ZONES(IPZ,0) = .TRUE.
+      CONNECTED_ZONES(0,IPZ) = 1
+      CONNECTED_ZONES(IPZ,0) = 1
    ELSEIF (WC%BOUNDARY_TYPE==INTERPOLATED_BOUNDARY) THEN
-      CONNECTED_ZONES(IOPZ,IPZ) = .TRUE.
-      CONNECTED_ZONES(IPZ,IOPZ) = .TRUE.
+      CONNECTED_ZONES(IOPZ,IPZ) = 1
+      CONNECTED_ZONES(IPZ,IOPZ) = 1
    ENDIF
 ENDDO
 
@@ -1294,7 +1294,7 @@ SUBROUTINE DIVERGENCE_PART_2(DT,NM)
    SUM_PSUM = PSUM(IPZ)
    DO IOPZ=N_ZONE,0,-1
       IF (IOPZ==IPZ) CYCLE
-      IF (CONNECTED_ZONES(IPZ,IOPZ)) THEN
+      IF (CONNECTED_ZONES(IPZ,IOPZ)>0) THEN
          IF (IOPZ==0) THEN
             OPEN_ZONE = .TRUE.
          ELSE
diff --git a/Source/hvac.f90 b/Source/hvac.f90
index 83d476e9bfa..3cb6ea6b799 100644
--- a/Source/hvac.f90
+++ b/Source/hvac.f90
@@ -1873,7 +1873,7 @@ SUBROUTINE DPSTARCALC
    PSUM_TOT(IPZ) = PSUM(IPZ)
    DO IOPZ = 1,N_ZONE
       IF (IPZ==IOPZ) CYCLE
-      IF (CONNECTED_ZONES(IPZ,IOPZ)) PSUM_TOT(IPZ) = PSUM_TOT(IPZ) + PSUM(IOPZ)
+      IF (CONNECTED_ZONES(IPZ,IOPZ)>0) PSUM_TOT(IPZ) = PSUM_TOT(IPZ) + PSUM(IOPZ)
    ENDDO
 ENDDO
 
@@ -1888,7 +1888,7 @@ SUBROUTINE DPSTARCALC
       DO IOPZ = 1, N_ZONE
          IF (IPZ==IOPZ) CYCLE
          IF (P_ZONE(IOPZ)%N_DUCTNODES==0) CYCLE
-         IF (CONNECTED_ZONES(IPZ,IOPZ)) THEN
+         IF (CONNECTED_ZONES(IPZ,IOPZ)>0) THEN
             IF (P_ZONE(IOPZ)%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)
@@ -3049,7 +3049,7 @@ SUBROUTINE COLLAPSE_HVAC_BC(T)
          WRITE(MESSAGE,'(A,A)') 'ERROR(552): Ductnode must lie with a single pressure zone. Node: ',TRIM(DUCTNODE(NN)%ID)
          CALL SHUTDOWN(MESSAGE); RETURN
       ENDIF
-      IF (CONNECTED_ZONES(0,DN%ZONE_INDEX)) DN%ZONE_INDEX = 0
+      IF (CONNECTED_ZONES(0,DN%ZONE_INDEX)>0) DN%ZONE_INDEX = 0
    ENDIF
 
    INTERNAL_NODE_IF: IF (((DN%VENT .OR. DN%LEAKAGE) .AND. .NOT. DN%AMBIENT) .OR. &
diff --git a/Source/main.f90 b/Source/main.f90
index 875609ba431..efbdfd624be 100644
--- a/Source/main.f90
+++ b/Source/main.f90
@@ -1361,13 +1361,7 @@ SUBROUTINE MPI_INITIALIZATION_CHORES(TASK_NUMBER)
 
       ! Allocate a few arrays needed to exchange divergence and pressure info among meshes
 
-      ALLOCATE(CONNECTED_ZONES(0:N_ZONE,0:N_ZONE),STAT=IZERO)
-      CALL ChkMemErr('INIT','CONNECTED_ZONES',IZERO)
-      CONNECTED_ZONES = .FALSE.
-
-      ALLOCATE(CONNECTED_ZONES_LOC(0:N_ZONE,0:N_ZONE),STAT=IZERO)
-      CALL ChkMemErr('INIT','CONNECTED_ZONES_LOC',IZERO)
-      CONNECTED_ZONES_LOC = 0
+      ALLOCATE(CONNECTED_ZONES(0:N_ZONE,0:N_ZONE),STAT=IZERO) ; CALL ChkMemErr('INIT','CONNECTED_ZONES',IZERO) ; CONNECTED_ZONES=0
 
       ALLOCATE(DSUM(N_ZONE),STAT=IZERO) ; CALL ChkMemErr('MAIN','DSUM',IZERO) ; DSUM = 0._EB
       ALLOCATE(PSUM(N_ZONE),STAT=IZERO) ; CALL ChkMemErr('MAIN','PSUM',IZERO) ; PSUM = 0._EB
@@ -1792,9 +1786,9 @@ SUBROUTINE INITIALIZE_DIVERGENCE_INTEGRALS
 DSUM = 0._EB
 
 IF (OBST_CREATED_OR_REMOVED) THEN
-   CONNECTED_ZONES = .FALSE.
+   CONNECTED_ZONES = 0
    DO IPZ=0,N_ZONE
-      CONNECTED_ZONES(IPZ,IPZ) = .TRUE.
+      CONNECTED_ZONES(IPZ,IPZ) = 1
    ENDDO
 ENDIF
 
@@ -1817,15 +1811,16 @@ SUBROUTINE EXCHANGE_DIVERGENCE_INFO
    CALL MPI_ALLREDUCE(MPI_IN_PLACE,DSUM,N_ZONE,MPI_DOUBLE_PRECISION,MPI_SUM,MPI_COMM_WORLD,IERR)
    CALL MPI_ALLREDUCE(MPI_IN_PLACE,PSUM,N_ZONE,MPI_DOUBLE_PRECISION,MPI_SUM,MPI_COMM_WORLD,IERR)
    CALL MPI_ALLREDUCE(MPI_IN_PLACE,USUM,N_ZONE,MPI_DOUBLE_PRECISION,MPI_SUM,MPI_COMM_WORLD,IERR)
-   CALL MPI_ALLREDUCE(MPI_IN_PLACE,CONNECTED_ZONES,(N_ZONE+1)**2,MPI_LOGICAL,MPI_LOR,MPI_COMM_WORLD,IERR)
 ENDIF
 
 ! Connect zones to others which are not directly connected
 
 IF (OBST_CREATED_OR_REMOVED) THEN
+   IF (N_MPI_PROCESSES>1) CALL MPI_ALLREDUCE(MPI_IN_PLACE,CONNECTED_ZONES,(N_ZONE+1)**2,MPI_INTEGER,MPI_SUM,MPI_COMM_WORLD,IERR)
    DO IPZ=1,N_ZONE
       CONNECTED_ZONES = MATMUL(CONNECTED_ZONES,CONNECTED_ZONES)
    ENDDO
+   CONNECTED_ZONES = MIN(1,CONNECTED_ZONES)
 ENDIF
 
 T_USED(11)=T_USED(11) + CURRENT_TIME() - TNOW
diff --git a/Source/pres.f90 b/Source/pres.f90
index 56c673748c4..6d25c49278a 100644
--- a/Source/pres.f90
+++ b/Source/pres.f90
@@ -1180,26 +1180,11 @@ SUBROUTINE ULMAT_SOLVER_SETUP(NM)
    CALL ChkMemErr('INIT','ZONE_MESH',IZERO)
 ENDIF
 
-! Identify connected ZONEs
+! Select the parent zone as the first in the row
 
-! translate logical array to local and fill diagonal
-CONNECTED_ZONES_LOC = 0
-DO IOPZ=0,N_ZONE
-   DO IPZ=0,N_ZONE
-      IF (IPZ==IOPZ .OR. CONNECTED_ZONES(IPZ,IOPZ)) CONNECTED_ZONES_LOC(IPZ,IOPZ) = 1
-   ENDDO
-ENDDO
-
-! establish sets of connected zones
-DO IPZ=1,N_ZONE
-   CONNECTED_ZONES_LOC = MATMUL(CONNECTED_ZONES_LOC,CONNECTED_ZONES_LOC)
-ENDDO
-CONNECTED_ZONES_LOC = MIN(1,CONNECTED_ZONES_LOC)
-
-! select the parent zone as the first in the row
 DO IPZ=0,N_ZONE
    ZM=>MESHES(NM)%ZONE_MESH(IPZ)
-   ZM%CONNECTED_ZONE_PARENT = MINLOC(CONNECTED_ZONES_LOC(IPZ,:), DIM=1, MASK = CONNECTED_ZONES_LOC(IPZ,:)/=0) - 1
+   ZM%CONNECTED_ZONE_PARENT = MINLOC(CONNECTED_ZONES(IPZ,:), DIM=1, MASK=CONNECTED_ZONES(IPZ,:)/=0) - 1
 ENDDO
 
 ! Test if FFT solver can be used for this MESH
@@ -1212,7 +1197,7 @@ SUBROUTINE ULMAT_SOLVER_SETUP(NM)
    IF (ZM%CONNECTED_ZONE_PARENT/=IPZ) CYCLE ZONE_MESH_LOOP
 
    ! Test for multiple zones in MESH
-   NZIM=SUM(CONNECTED_ZONES_LOC(IPZ,:))
+   NZIM=SUM(CONNECTED_ZONES(IPZ,:))
    IF (NZIM>1) ZM%USE_FFT=.FALSE.
    IPZIM=IPZ
 
@@ -4827,24 +4812,11 @@ SUBROUTINE GET_MATRIX_INDEXES_H
 DO NM=LOWER_MESH_INDEX,UPPER_MESH_INDEX
    ! Initialize unknown numbers for H:
    MESHES(NM)%CCVAR(:,:,:,UNKH) = IS_UNDEFINED
-   ! Identify connected ZONEs
-   ! translate logical array to local and fill diagonal
-   CONNECTED_ZONES_LOC = 0
-   DO IOPZ=0,N_ZONE
-      DO IPZ=0,N_ZONE
-         IF (IPZ==IOPZ .OR. CONNECTED_ZONES(IPZ,IOPZ)) CONNECTED_ZONES_LOC(IPZ,IOPZ) = 1
-      ENDDO
-   ENDDO
-   ! establish sets of connected zones
-   DO IPZ=1,N_ZONE
-      CONNECTED_ZONES_LOC = MATMUL(CONNECTED_ZONES_LOC,CONNECTED_ZONES_LOC)
-   ENDDO
-   CONNECTED_ZONES_LOC = MIN(1,CONNECTED_ZONES_LOC)
-   ! select the parent zone as the first in the row
+   ! Select the parent zone as the first in the row
    DO IPZ=0,N_ZONE
       ZSL => ZONE_SOLVE(IPZ)
       IF(.NOT.PRES_ON_WHOLE_DOMAIN) &
-      ZSL%CONNECTED_ZONE_PARENT = MINLOC(CONNECTED_ZONES_LOC(IPZ,:), DIM=1, MASK = CONNECTED_ZONES_LOC(IPZ,:)/=0) - 1
+      ZSL%CONNECTED_ZONE_PARENT = MINLOC(CONNECTED_ZONES(IPZ,:), DIM=1, MASK=CONNECTED_ZONES(IPZ,:)/=0) - 1
    ENDDO
 ENDDO