Which is better propane or coal forge?
Gas burns cleaner than a coal forge and is readily available. Some of the drawbacks to using gas is that it's noisier, and it makes the shop hotter in the summer time. Depending on the type of smithing that your doing gas is also generally considered more expensive than coal.
Propane forge is arguable the best type of forge for beginner blacksmiths. They are affordable, easy to clean, easy to use, and can keep a constant temperature at ease.
It has one indisputable advantage over gas: It gets much hotter. Glowing coals are at a temperature of about 2,000 degrees Fahrenheit; while gas burns at around 3,500 degrees Fahrenheit, there's very little radiant heat from the flames. Charcoal purists will tell you their preferred fuel leads to better flavor.
A 100lb tank is about 80$ to refill for me and lasts around 16-18 hours of forging, so about $5 hour to run it.
It is extremely important to work in a well-ventilated area outdoors when you are building a forge at home. A well-ventilated workspace prevents the buildup of carbon monoxide. If you are working in a garage, open the garage door and install a carbon monoxide detector.
Coal typically burns the hottest of them all, so if you're looking to work with metals with high melting points, a coal solid fuel forge is ideal for you.
Bituminous is the coal-of-choice for the blacksmith. It is a soft, mid-grade, black coal. Mined from deeper mines than lignite, it burns much more cleanly.
Cold forging improves the strength of the metal by hardening it at room temperature. Hot forging results in optimal yield strength, low hardness, and high ductility by hardening the metal at extremely high temperatures.
The rule of thumb for the vent is at least seven times the cross sectional area of the burner.
As a general rule of thumb, propane is cheaper per BTU than heating oil. However, seasonal factors and location also play a role.
What gives out more heat wood or coal?
While coal tends to burn hotter, we know enough about various kinds of wood and how to treat them to create hot-burning, consistent logs from the cultured forests grown. Once it is harvested, the wood is cured to remove excess moisture, which allows it to burn hotter and thereby cleaner.
Charcoal Versus Gas
Assuming that it costs $15 USD to fill a 20-pound propane bottle that gives you 25 cookouts and that 20 pounds of charcoal runs around $10 USD and gives you three cookouts you will spend about $. 60 USD per every time you fire up the gas grill and around $3.50 on the charcoal grill.

In terms of smoke and flavor, charcoal grills not only smoke meats better than gas, they also release a chemical called guaiacol. Guaiacol is an aroma compound that gives meat a smoky, bacon-like flavor, and it only comes from wood and charcoal.
Bituminous is the coal-of-choice for the blacksmith. It is a soft, mid-grade, black coal. Mined from deeper mines than lignite, it burns much more cleanly.
Coal is widely considered the best fuel for forging. Coal burns hotter and more efficiently compared to charcoal and wood. It is also less expensive and more readily available than propane. Also, the coal volume required to run a forge is considerably lesser than charcoal, wood, and propane.
Charcoal Versus Gas
Gas grills typically cost more than charcoal grills, but they cost less to use. Assuming that it costs $15 USD to fill a 20-pound propane bottle that gives you 25 cookouts and that 20 pounds of charcoal runs around $10 USD and gives you three cookouts you will spend about $.