diff --git a/code/modules/atmospherics/machinery/components/unary_devices/heat_exchanger.dm b/code/modules/atmospherics/machinery/components/unary_devices/heat_exchanger.dm
index c0dfc5633e..4ad3bbf575 100644
--- a/code/modules/atmospherics/machinery/components/unary_devices/heat_exchanger.dm
+++ b/code/modules/atmospherics/machinery/components/unary_devices/heat_exchanger.dm
@@ -12,6 +12,8 @@
 
 	var/obj/machinery/atmospherics/components/unary/heat_exchanger/partner = null
 	var/update_cycle
+	var/old_temperature = 0
+	var/other_old_temperature = 0
 
 	pipe_state = "heunary"
 
@@ -59,9 +61,6 @@
 	var/other_air_heat_capacity = partner_air_contents.heat_capacity()
 	var/combined_heat_capacity = other_air_heat_capacity + air_heat_capacity
 
-	var/old_temperature = air_contents.return_temperature()
-	var/other_old_temperature = partner_air_contents.return_temperature()
-
 	if(combined_heat_capacity > 0)
 		var/combined_energy = partner_air_contents.return_temperature()*other_air_heat_capacity + air_heat_capacity*air_contents.return_temperature()
 
@@ -71,6 +70,8 @@
 
 	if(abs(old_temperature-air_contents.return_temperature()) > 1)
 		update_parents()
+		old_temperature = air_contents.return_temperature()
 
 	if(abs(other_old_temperature-partner_air_contents.return_temperature()) > 1)
 		partner.update_parents()
+		other_old_temperature = partner_air_contents.return_temperature()