- Homepage -

Oil fired furnace Vs. Small cupola

For melting iron

This page is a comparison between melting iron in a crucible with a waste oil burner and melting iron in a cupola with coal or coke. Overall these two methods are the most practical and economical ways for a hobbyist to melt iron. The best attributes are in green text, while the drawbacks are in red text. - Aug./10/2007

Other matchups; Charcoal Vs. Propane | Propane Vs. Waste oil | Used motor oil Vs. Used cooking oil.

Used cooking oil Vs. small cupola

Oil fired furnace
Small cupola furnace
Oil to fuel the furnace must usually be obtained from outside sources even when collected from them for free. Cupola furnaces can be run off homemade hardwood charcoal making you completely self sufficient in terms of fuel.
An oil fired furnace can melt large chunks of iron as long as they fit in the crucible. Cupola furnaces require the metal to be broken into fairly specific size pieces or they won't melt properly.
A waste oil burner can have your iron ready to pour within 30-40 minutes of ignition. Many cupolas require a preheat time of up to an hour for the first charge of iron to preheat before any melting can begin.
In general iron melts slower in a crucible even with a strong oil burner. After the first batch of metal melts each seceding batch of metal can usually be poured in 8-10 minutes.
An oil fired furnace's iron melting capacity is mostly limited only by the size of crucible available or that can fit inside the furnace. Cupolas are generally limited to a set amount of iron per batch based on their bore size.
Unless a crucible breaks iron is not likely to freeze in a oil fired furnace. Iron can easily freeze in the cupola well or tap hole sometimes requiring major work to remove it.
An oil fired furnace requires a crucible to hold the metal. Crucibles can be expensive. A cupola does not require a crucible.
An oil fired furnace can be short and compact like most other crucible furnaces. Cupolas are narrow but they are usually tall which can make them more challenging to move.
If the oil burner malfunctions it can produce a lot of smoke. Unless the cupola is burning dirty coal there is little to no smoke from it.
After the iron melt you shut off the burner and you're done. After the iron melt you have to clean ash, coals, hot slag and leftover iron from inside the furnace.
If you need large individual loads of iron or a few occasional pours then a waste oil fired furnace is a great way to go. However if you need multiple, rapid iron pours per melting session and each individual pour doesn't need to be very large than a cupola is a great option. A cupola is especially valuable when molds are being made continuously by several people and then poured as soon as they are ready.