diff --git a/property_packages/modular/builder/common_parsers.py b/property_packages/modular/builder/common_parsers.py
index 145c456..73a1591 100644
--- a/property_packages/modular/builder/common_parsers.py
+++ b/property_packages/modular/builder/common_parsers.py
@@ -274,6 +274,12 @@ def serialise(compounds: List[Compound], valid_states: List[States]) -> Dict[str
                 "temperature": (min_melting_point, 200, 400, pyunits.K),
                 "pressure": (5e4, 1e5, 1e6, pyunits.Pa),
             }
+        elif (min_critical_temperature > 120):
+            return {
+                "flow_mol": (0, 100, 1000, pyunits.mol / pyunits.s),
+                "temperature": (min_melting_point, 150, 500, pyunits.K),
+                "pressure": (5e4, 1e5, 1e6, pyunits.Pa),
+            }
         else:
             return {
                 "flow_mol": (0, 100, 1000, pyunits.mol / pyunits.s),
diff --git a/property_packages/tests/test_heat_exchanger_bt_pr.py b/property_packages/tests/test_heat_exchanger_pr.py
similarity index 58%
rename from property_packages/tests/test_heat_exchanger_bt_pr.py
rename to property_packages/tests/test_heat_exchanger_pr.py
index 6be9506..dc2281b 100644
--- a/property_packages/tests/test_heat_exchanger_bt_pr.py
+++ b/property_packages/tests/test_heat_exchanger_pr.py
@@ -18,7 +18,7 @@ def assert_approx(value, expected_value, error_margin):
     tolerance = abs(percent_error * expected_value)
     assert approx(value, abs=tolerance) == expected_value
 
-def test_heat_exchanger():
+def test_heat_exchanger_bt():
     m = ConcreteModel()
     m.fs = FlowsheetBlock(dynamic=False)
 
@@ -60,4 +60,48 @@ def test_heat_exchanger():
     result = solver.solve(m)
 
     assert value(m.fs.heat_exchanger.shell.properties_out[0].temperature) == approx(373.13, abs=1e-2)
-    assert_approx(value(m.fs.heat_exchanger.tube.properties_out[0].temperature), 369.24, 0.5)
\ No newline at end of file
+    assert_approx(value(m.fs.heat_exchanger.tube.properties_out[0].temperature), 369.24, 0.5)
+
+def test_heat_exchanger_asu():
+    m = ConcreteModel()
+    m.fs = FlowsheetBlock(dynamic=False)
+
+    m.fs.properties1 = build_package("helmholtz", ["h2o"], ["Liq", "Vap"])
+    m.fs.properties2 = build_package("peng-robinson", ["oxygen", "argon", "nitrogen"], ["Liq", "Vap"])
+    
+    m.fs.heat_exchanger = HeatExchanger(
+        delta_temperature_callback=delta_temperature_amtd_callback,
+        hot_side_name="shell",
+        cold_side_name="tube",
+        shell={"property_package": m.fs.properties1},
+        tube={"property_package": m.fs.properties2})
+    
+    assert degrees_of_freedom(m) == 11
+
+    h = htpx(473.15*units.K, P = 100000*units.Pa) # 200 C
+    m.fs.heat_exchanger.shell_inlet.flow_mol.fix(20*units.kilomol/units.hour)
+    m.fs.heat_exchanger.shell_inlet.pressure.fix(100000) # Pa
+    m.fs.heat_exchanger.shell_inlet.enth_mol.fix(h) # J/mol
+
+    assert degrees_of_freedom(m) == 8
+
+    m.fs.heat_exchanger.tube_inlet.flow_mol.fix(1*units.kilomol/units.hour) # mol/s
+    m.fs.heat_exchanger.tube_inlet.mole_frac_comp[0, "oxygen"].fix(0.33)
+    m.fs.heat_exchanger.tube_inlet.mole_frac_comp[0, "argon"].fix(0.33)
+    m.fs.heat_exchanger.tube_inlet.mole_frac_comp[0, "nitrogen"].fix(0.33)
+    m.fs.heat_exchanger.tube_inlet.pressure.fix(100000) # Pa
+    m.fs.heat_exchanger.tube_inlet.temperature[0].fix((25 + 273.15)*units.K)
+
+    assert degrees_of_freedom(m) == 2
+
+    m.fs.heat_exchanger.shell_outlet.pressure.fix(100000)
+    m.fs.heat_exchanger.heat_duty.fix(927.7) # W
+
+    assert degrees_of_freedom(m) == 0
+
+    m.fs.heat_exchanger.initialize()
+
+    solver = SolverFactory('ipopt')
+    result = solver.solve(m)
+    
+    assert_approx(value(m.fs.heat_exchanger.shell.properties_out[0].temperature), 195.3 + 273.15, 0.1)
\ No newline at end of file
diff --git a/property_packages/tests/test_heater_bt_pr.py b/property_packages/tests/test_heater_bt_pr.py
deleted file mode 100644
index ea0cc94..0000000
--- a/property_packages/tests/test_heater_bt_pr.py
+++ /dev/null
@@ -1,42 +0,0 @@
-# Build and solve a heater block.
-from ..build_package import build_package
-from pytest import approx
-
-# Import objects from pyomo package 
-from pyomo.environ import ConcreteModel, SolverFactory, value, units
-
-# Import the main FlowsheetBlock from IDAES. The flowsheet block will contain the unit model
-from idaes.core import FlowsheetBlock
-from idaes.core.util.model_statistics import degrees_of_freedom
-from idaes.models.unit_models.heater import Heater
-from idaes.core.util.tables import _get_state_from_port
-
-def assert_approx(value, expected_value, error_margin):
-    percent_error = error_margin / 100
-    tolerance = abs(percent_error * expected_value)
-    assert approx(value, abs=tolerance) == expected_value
-
-def test_heater():
-    m = ConcreteModel()
-    m.fs = FlowsheetBlock(dynamic=False) 
-    m.fs.properties = build_package("peng-robinson", ["benzene", "toluene"], ["Liq", "Vap"])
-    
-    m.fs.heater = Heater(property_package=m.fs.properties)
-
-    m.fs.heater.inlet.flow_mol.fix(1000/3600)
-    m.fs.heater.inlet.mole_frac_comp[0, "benzene"].fix(0.4)
-    m.fs.heater.inlet.mole_frac_comp[0, "toluene"].fix(0.6)
-    m.fs.heater.inlet.pressure.fix(101325)
-    m.fs.heater.inlet.temperature.fix(353)
-    m.fs.heater.heat_duty.fix(459.10147722222354)
-
-    m.fs.heater.initialize()
-
-    assert degrees_of_freedom(m) == 0
-
-    solver = SolverFactory('ipopt')
-    solver.solve(m, tee=True)
-
-    assert_approx(value(_get_state_from_port(m.fs.heater.outlet,0).temperature), 363, 0.2)
-    assert value(m.fs.heater.outlet.pressure[0]) == approx(101325)
-    assert value(m.fs.heater.outlet.flow_mol[0]) == approx(1000/3600)
\ No newline at end of file
diff --git a/property_packages/tests/test_heater_pr.py b/property_packages/tests/test_heater_pr.py
new file mode 100644
index 0000000..06760e5
--- /dev/null
+++ b/property_packages/tests/test_heater_pr.py
@@ -0,0 +1,85 @@
+# Build and solve a heater block.
+from ..build_package import build_package
+from pytest import approx
+
+# Import objects from pyomo package 
+from pyomo.environ import ConcreteModel, SolverFactory, value, units
+
+# Import the main FlowsheetBlock from IDAES. The flowsheet block will contain the unit model
+from idaes.core import FlowsheetBlock
+from idaes.core.util.model_statistics import degrees_of_freedom
+from idaes.models.unit_models.heater import Heater
+from idaes.core.util.tables import _get_state_from_port
+
+def assert_approx(value, expected_value, error_margin):
+    percent_error = error_margin / 100
+    tolerance = abs(percent_error * expected_value)
+    assert approx(value, abs=tolerance) == expected_value
+
+def test_heater_bt():
+    m = ConcreteModel()
+    m.fs = FlowsheetBlock(dynamic=False) 
+    m.fs.properties = build_package("peng-robinson", ["benzene", "toluene"], ["Liq", "Vap"])
+    
+    m.fs.heater = Heater(property_package=m.fs.properties)
+
+    m.fs.heater.inlet.flow_mol.fix(1000/3600)
+    m.fs.heater.inlet.mole_frac_comp[0, "benzene"].fix(0.4)
+    m.fs.heater.inlet.mole_frac_comp[0, "toluene"].fix(0.6)
+    m.fs.heater.inlet.pressure.fix(101325)
+    m.fs.heater.inlet.temperature.fix(353)
+    m.fs.heater.heat_duty.fix(459.10147722222354)
+
+    m.fs.heater.initialize()
+
+    assert degrees_of_freedom(m) == 0
+
+    solver = SolverFactory('ipopt')
+    solver.solve(m, tee=True)
+
+    assert_approx(value(_get_state_from_port(m.fs.heater.outlet,0).temperature), 363, 0.2)
+    assert value(m.fs.heater.outlet.pressure[0]) == approx(101325)
+    assert value(m.fs.heater.outlet.flow_mol[0]) == approx(1000/3600)
+
+def test_heater_asu():
+    m = ConcreteModel()
+    m.fs = FlowsheetBlock(dynamic=False) 
+    m.fs.properties = build_package("peng-robinson", ["argon", "nitrogen", "oxygen"], ["Liq", "Vap"])
+    
+    m.fs.heater = Heater(property_package=m.fs.properties)
+
+    m.fs.heater.inlet.flow_mol.fix(units.convert(1 * units.kilomol/units.hour, units.mol/units.s)) # mol/s
+    m.fs.heater.inlet.mole_frac_comp[0, "argon"].fix(0.33)
+    m.fs.heater.inlet.mole_frac_comp[0, "nitrogen"].fix(0.33)
+    m.fs.heater.inlet.mole_frac_comp[0, "oxygen"].fix(0.33)
+    m.fs.heater.inlet.pressure.fix(100000)
+    m.fs.heater.inlet.temperature.fix(units.convert_temp_C_to_K(25))
+    m.fs.heater.outlet.temperature.fix(units.convert_temp_C_to_K(50))
+
+    m.fs.heater.initialize()
+
+    assert degrees_of_freedom(m) == 0
+
+    solver = SolverFactory('ipopt')
+    solver.solve(m, tee=True)
+
+    assert_approx(value(m.fs.heater.heat_duty[0]), 183.856, 1) # 1% tolerance
+
+    m.fs.heater2 = Heater(property_package=m.fs.properties)
+
+    m.fs.heater2.inlet.flow_mol.fix(units.convert(1 * units.kilomol/units.hour, units.mol/units.s)) # mol/s
+    m.fs.heater2.inlet.mole_frac_comp[0, "argon"].fix(0.33)
+    m.fs.heater2.inlet.mole_frac_comp[0, "nitrogen"].fix(0.33)
+    m.fs.heater2.inlet.mole_frac_comp[0, "oxygen"].fix(0.33)
+    m.fs.heater2.inlet.pressure.fix(100000)
+    m.fs.heater2.inlet.temperature.fix(units.convert_temp_C_to_K(25))
+    m.fs.heater2.outlet.temperature.fix(units.convert_temp_C_to_K(-15))
+
+    m.fs.heater2.initialize()
+
+    assert degrees_of_freedom(m) == 0
+
+    solver = SolverFactory('ipopt')
+    solver.solve(m, tee=True)
+
+    assert_approx(value(m.fs.heater2.heat_duty[0]), -292.5, 1) # 1% tolerance