For a lower cost to enter, with OSRS GP recommend gaining access to the Ring of Charos (a). However, avoid using the pay option when using that Blast Furnace foreman because it can void the benefits of the ring. You can get this ring by completing The Creature of Fenkenstrain questline.
Bring Ice Gloves to the Blast Furnace can be helpful when making use of the bar dispenser as it will cool them off quickly for you to grab. This will cut down on time, instead of having buckets of water repeatedly to cool the bars (and it'll free up space in the inventory too).
Before you get started on this journey towards the Blast Furnace itself, it is worth noting that it's only available in the following worlds: 352 (355), 355, 358 386, and 387. Once you've spoken the Giant Dwarf and walked to Keldagrim, you need to turn north and work your way across the bridge. Once you've completed the crossing, continue to go south until you see an Blast Furnace icon on the map. Enter the building marked go downstairs, and you'll find the furnace.
After you've done this you'll have a much easier time to travel to the site at a later time. You can make use of this Grand Exchange shortcut on the northwest wall, or take a trip in the minecart and explore Ice Mountain Dwarven mines, or make use of buy RS gold the minigame group locater that will let you enter the building.
