diff --git a/src/pybamm/models/submodels/thermal/base_thermal.py b/src/pybamm/models/submodels/thermal/base_thermal.py
index 42d90f1bcf..384cb1723a 100644
--- a/src/pybamm/models/submodels/thermal/base_thermal.py
+++ b/src/pybamm/models/submodels/thermal/base_thermal.py
@@ -143,8 +143,12 @@ def _get_standard_coupled_variables(self, variables):
             phase_names = ["primary ", "secondary "]
 
         if self.options.electrode_types["negative"] == "planar":
-            Q_rxn_n = pybamm.FullBroadcast(
-                0, ["negative electrode"], "current collector"
+            i_n = variables["Lithium metal total interfacial current density [A.m-2]"]
+            eta_r_n = variables["Lithium metal interface reaction overpotential [V]"]
+            Q_rxn_n = pybamm.PrimaryBroadcast(
+                i_n * eta_r_n / self.param.n.L,
+                ["negative electrode"],
+                "current collector",
             )
             Q_rev_n = pybamm.FullBroadcast(
                 0, ["negative electrode"], "current collector"