As long as the heater does not have an open flame and does not produce any condensation, then you are able to use it during the application phase.
Epoxy will not cure if applied under 7°C, so be advised that if the temperature drops over night after application, the curing time will slow down.
When storing, it is advisable to keep the products in a room at ambient temperature. Epoxy should not be placed near heaters or warmed up in any way, when in storage.