diff --git a/src/HPWH.cc b/src/HPWH.cc
index 95db6556..9cb5c930 100644
--- a/src/HPWH.cc
+++ b/src/HPWH.cc
@@ -102,6 +102,12 @@ HPWH::ConversionMap<HPWH::L_UNITS> HPWH::convertL = {
     {std::make_pair(HPWH::L_UNITS::M, HPWH::L_UNITS::FT), &M_TO_FT},
     {std::make_pair(HPWH::L_UNITS::FT, HPWH::L_UNITS::M), &FT_TO_M}};
 
+HPWH::ConversionMap<HPWH::A_UNITS> HPWH::convertA = {
+    {std::make_pair(HPWH::A_UNITS::M2, HPWH::A_UNITS::M2), &ident},
+    {std::make_pair(HPWH::A_UNITS::FT2, HPWH::A_UNITS::FT2), &ident},
+    {std::make_pair(HPWH::A_UNITS::M2, HPWH::A_UNITS::FT2), &M2_TO_FT2},
+    {std::make_pair(HPWH::A_UNITS::FT2, HPWH::A_UNITS::M2), &FT2_TO_M2}};
+
 HPWH::ConversionMap<HPWH::V_UNITS> HPWH::convertV = {
     {std::make_pair(HPWH::V_UNITS::L, HPWH::V_UNITS::L), ident},
     {std::make_pair(HPWH::V_UNITS::GAL, HPWH::V_UNITS::GAL), ident},
@@ -1322,15 +1328,15 @@ int HPWH::setTankSize_adjustUA(double HPWH_size, V_UNITS units /*L*/, bool force
     // Uses the UA before the function is called and adjusts the A part of the UA to match
     // the input volume given getTankSurfaceArea().
     double HPWH_size_L = convert(HPWH_size, units, V_UNITS::L);
-    double oldA = getTankSurfaceArea(UNITS_FT2);
+    double oldA_ft2 = getTankSurfaceArea(A_UNITS::FT2);
 
     setTankSize(HPWH_size_L, V_UNITS::L, forceChange);
-    setUA(tankUA_kJperHrC / oldA * getTankSurfaceArea(UNITS_FT2), UA_UNITS::KJperHC);
+    setUA(tankUA_kJperHrC * getTankSurfaceArea(A_UNITS::FT2) / oldA_ft2, UA_UNITS::KJperHC);
     return 0;
 }
 
 /*static*/ double
-HPWH::getTankSurfaceArea(double vol, V_UNITS volUnits /*L*/, UNITS surfAUnits /*=UNITS_FT2*/)
+HPWH::getTankSurfaceArea(double vol, const V_UNITS volUnits /*L*/, const A_UNITS surfAUnits /*FT2*/)
 {
     // returns tank surface area, old defualt was in ft2
     // Based off 88 insulated storage tanks currently available on the market from Sanden,
@@ -1338,34 +1344,12 @@ HPWH::getTankSurfaceArea(double vol, V_UNITS volUnits /*L*/, UNITS surfAUnits /*
     // tankVolume_L with the assumption that the aspect ratio is the same as the outer
     // dimenisions of the whole unit.
     double radius = getTankRadius(vol, volUnits, L_UNITS::FT);
-
-    double value = 2. * Pi * pow(radius, 2) * (ASPECTRATIO + 1.);
-
-    if (value >= 0.)
-    {
-        if (surfAUnits == UNITS_M2)
-            value = FT2_TO_M2(value);
-        else if (surfAUnits != UNITS_FT2)
-            value = -1.;
-    }
-    return value;
+    return convert(2. * Pi * pow(radius, 2) * (ASPECTRATIO + 1.), A_UNITS::FT2, surfAUnits);
 }
 
-double HPWH::getTankSurfaceArea(UNITS units /*=UNITS_FT2*/) const
+double HPWH::getTankSurfaceArea(const A_UNITS units /*FT2*/) const
 {
-    // returns tank surface area, old defualt was in ft2
-    // Based off 88 insulated storage tanks currently available on the market from Sanden,
-    // AOSmith, HTP, Rheem, and Niles. Corresponds to the inner tank with volume
-    // tankVolume_L with the assumption that the aspect ratio is the same as the outer
-    // dimenisions of the whole unit.
-    double value = getTankSurfaceArea(tankVolume_L, V_UNITS::L, units);
-    if (value < 0.)
-    {
-        if (hpwhVerbosity >= VRB_reluctant)
-            msg("Incorrect unit specification for getTankSurfaceArea.  \n");
-        value = HPWH_ABORT;
-    }
-    return value;
+    return getTankSurfaceArea(tankVolume_L, V_UNITS::L, units);
 }
 
 /*static*/ double
diff --git a/src/HPWH.hh b/src/HPWH.hh
index 2b3403ff..47407ece 100644
--- a/src/HPWH.hh
+++ b/src/HPWH.hh
@@ -262,12 +262,6 @@ class HPWH
         VRB_emetic = 30     /**< print all the things  */
     };
 
-    enum UNITS
-    {
-        UNITS_FT2, /**< square feet  */
-        UNITS_M2   /**< square meters  */
-    };
-
     struct PairHash
     {
         template <class T>
@@ -347,7 +341,7 @@ class HPWH
     /* length units and conversion */
     enum class L_UNITS
     {
-        M, // meteres
+        M, // meters
         FT // feet
     };
     static ConversionMap<L_UNITS> convertL;
@@ -357,6 +351,19 @@ class HPWH
         return convertL[{fromUnits, toUnits}](length);
     }
 
+    /* area units and conversion */
+    enum class A_UNITS
+    {
+        M2, // square meters
+        FT2 // square feet
+    };
+    static ConversionMap<A_UNITS> convertA;
+    inline static double
+    convert(const double length, const HPWH::A_UNITS fromUnits, const HPWH::A_UNITS toUnits)
+    {
+        return convertA[{fromUnits, toUnits}](length);
+    }
+
     /* volume units and conversion */
     enum class V_UNITS
     {
@@ -862,10 +869,11 @@ class HPWH
     /**< This sets the tank size and adjusts the UA the HPWH currently has to have the same U value
        but a new A. A is found via getTankSurfaceArea()*/
 
-    double getTankSurfaceArea(UNITS units = UNITS_FT2) const;
+    double getTankSurfaceArea(const A_UNITS units = A_UNITS::FT2) const;
 
-    static double
-    getTankSurfaceArea(double vol, V_UNITS volUnits = V_UNITS::L, UNITS surfAUnits = UNITS_FT2);
+    static double getTankSurfaceArea(double vol,
+                                     V_UNITS volUnits = V_UNITS::L,
+                                     A_UNITS surfAUnits = A_UNITS::FT2);
 
     /**< Returns the tank surface area based off of real storage tanks*/
     double getTankRadius(const L_UNITS units = L_UNITS::FT) const;
@@ -1765,6 +1773,10 @@ inline double W_TO_BTUperH(const double W) { return KW_TO_BTUperH(W_TO_KW(W)); }
 inline double M_TO_FT(const double m) { return ft_per_m * m; }
 inline double FT_TO_M(const double ft) { return ft / ft_per_m; }
 
+// area conversion
+inline double M2_TO_FT2(const double m2) { return (ft_per_m * ft_per_m * m2); }
+inline double FT2_TO_M2(const double ft2) { return (ft2 / ft_per_m / ft_per_m); }
+
 // volume conversion
 inline double L_TO_GAL(const double L) { return gal_per_L * L; }
 inline double GAL_TO_L(const double gal) { return gal / gal_per_L; }
@@ -1779,9 +1791,6 @@ inline double FT3_TO_GAL(const double ft3) { return L_TO_GAL(FT3_TO_L(ft3)); }
 inline double GPM_TO_LPS(const double gpm) { return (gpm / gal_per_L / sec_per_min); }
 inline double LPS_TO_GPM(const double lps) { return (gal_per_L * lps * sec_per_min); }
 
-// area conversion
-inline double FT2_TO_M2(const double ft2) { return (ft2 / ft_per_m / ft_per_m); }
-
 // UA conversion
 inline double KJperHC_TO_BTUperHF(const double UA_kJperhC)
 {
diff --git a/src/HPWHpresets.cc b/src/HPWHpresets.cc
index 13295f15..c5253cff 100644
--- a/src/HPWHpresets.cc
+++ b/src/HPWHpresets.cc
@@ -235,7 +235,7 @@ int HPWH::HPWHinit_resTankGeneric(double tankVol_L,
     }
 
     // Calc UA
-    double SA_M2 = getTankSurfaceArea(tankVol_L, HPWH::V_UNITS::L, HPWH::UNITS_M2);
+    double SA_M2 = getTankSurfaceArea(tankVol_L, HPWH::V_UNITS::L, HPWH::A_UNITS::M2);
     double tankUA_WperK = SA_M2 / rValue_M2KperW;
     tankUA_kJperHrC = tankUA_WperK * 3.6; // 3.6 = 3600 S/Hr and 1/1000 kJ/J