Storage Heaters Charge up over night using the 7 hrs of economy 7. Manual Storage Heaters charge for the full 7 hours regardless of how much heat it used the previous day. Automatic Storage Heaters calulate how much heat was used the previous day and work out how long they need to charge for. For example, If an automatic storage heater only used 5 out of the 7 hours of stored heat, when it comes to the next charging time the storage heater will wait 2 hours then will charge till it is full. On Average this facility can save you up to 15%.