“The Furnace spawns two Fire Spirits at a time. It also makes great brick-oven pancakes.”
The Furnace card is unlocked from the Spell Valley (Arena 5). It is a moderate hitpoint building that spawns a pair of Fire Spirits every 10 seconds. A Furnace card costs 4 Elixir to deploy. It appears to be a cast-iron steam train furnace with a bubbling cauldron of Elixir on top of it. It is also covered with various other props, including a ladder on the side of it, and a pile of firewood on the other.
The Furnace can spawn up to 12 Fire Spirits over its lifetime, which would cost 8 Elixir to deploy manually, creating a profit of 4 Elixir.
The Furnace can be used with other spawner buildings to deal high instant splash damage.
Mirroring it can spawn four Fire Spirits at a time, which provides fast and heavy area damage support for tanks. However, the Fire Spirits themselves are weak to area damage cards like spells, and placing the second Furnace close to the first can allow the opponent to get a large positive Elixir trade by targeting both buildings at one.
It can act as a useful defense along with being a support building, thanks to its Fire Spirits which deal area damage.
The Furnace is effective at preventing spawner decks from building momentum due to the fact that the Fire Spirits spawned deal splash damage.
The Furnace is good at supporting counterattacks as it takes out many small troops, such as Minions, Spear Goblins, and Goblins, that opponents may play due to being low on Elixir from their attack. Prepared in advance, the player will not have to worry about cards like Minions, as the spawned Fire Spirits take care of them on their own.
If no other options are available, a Furnace can stop a push with low hitpoints troops since it will immediately spawn at least one Fire Spirit, wiping out a lot of the push and acting as a distraction.
Keep in mind that at Tournament Rules levels, one of the spawned Fire Spirits will be able to attack the tower. Due to the Furnace's 50 second lifetime, this will deal valuable chip damage to a tower.
Mini P.E.K.K.A. is a great pair with the Furnace's Fire Spirits, as the Fire Spirits take out any Goblins, or multiple troop card (excluding Skeleton Army), while Mini P.E.K.K.A.'s priority is the tower.
Poison is a powerful counter to the Furnace, as it will not only damage the spawner but will also most likely take out the Fire Spirits.
Since the Fire Spirits spawned from the Furnace explode on impact, Skeletons from the Tombstone can distract Fire Spirits easily and stop almost all the waves of Fire Spirits.
The Furnace is a great support card if placed behind a tank, eliminating nearly any type of cheap card that the enemy will place down to counter it. For example, a great combo is Hog Rider or Giant Skeleton with a Furnace. If the opponent spawns cards such as Minions or Goblins to either distract or destroy, the Fire Spirits will take them out, and if left unchecked behind a tank can decimate the tower with their powerful splash.
A Princess can take out the Furnace without any support if she is left uncountered.
The Bowler and Executioner are decent counters to the Furnace. Their linear attack allows them to hit the Furnace without being damaged by the Fire Spirits.
It is the only building unlocked at Arena 5 (Spell Valley).
It is the second spawner building to not take the appearance of a 'Hut', the first being the Tombstone.
It seems that it has Elixir in the pot.
The pot on top of the Furnace resembles the Cauldron decoration from Clash of Clans. The pot on top of the Furnace also jumps into the air when spawning Fire Spirits, although an Ice Wizard or stunning spells can cause the pot to desynchronise with the Fire Spirits spawning.
If 3 Fire Spirits cost 2 Elixir, the Furnace needs to spawn the Fire Spirits 4 times to be a profit over the actual Fire Spirits card.
The Furnace's description could be a reference towards the Mini P.E.K.K.A. since the Mini P.E.K.K.A says "pancakes" when it is deployed.
It was the first of the two buildings added after Clash Royale's soft launch.