Propane Forge Cost Calculator
Quick answer
Enter your forge burner's BTU/hr, your tank size and your local refill price, and this calculator returns your propane cost per hour, forging hours per tank, and how many 2-hour sessions you get. It also warns you when your burner will out-draw a small tank and freeze it. Defaults show a 90,000 BTU/hr single burner on a 20 lb tank at $22.
Your propane cost
Based on 90,000 BTU/hr at 80% duty (72,000 BTU/hr effective) from a 20 lb tank at $22.00.
| Tank | Usable BTU (full) | Forging hours | 2-hr sessions | Safe draw (BTU/hr, 60°F) |
|---|---|---|---|---|
| 20 lb | 430,960 | 6.0 h | 2 | 80,000 |
| 30 lb | 646,440 | 9.0 h | 4 | 105,000 |
| 40 lb | 861,920 | 12.0 h | 5 | 130,000 |
| 100 lb | 2,154,800 | 29.9 h | 14 | 200,000 |
How the propane forge cost is calculated
Propane holds about 21,548 BTU per pound. The math is simple:
- Usable energy in the tank = fill weight x 21,548 BTU/lb
- Effective burner load = your BTU/hr x duty cycle
- Forging hours = tank energy / effective load
- Cost per hour = your refill price / forging hours
The duty cycle matters because you are not on full gas the whole time - you pull the work, hammer it, and reheat. 80% is a fair default for active forging; drop it toward 60% for slow, thoughtful work and raise it toward 100% for constant welding heat. A 20 lb tank holds 430,960 BTU, so at 72,000 BTU/hr effective it lasts about 6.0 hours.
Why a small tank freezes on a big burner
Liquid propane has to boil into gas before it can burn, and that boiling pulls heat out of the tank. Ask a small tank for too much gas and it gets so cold that frost forms on the outside, the pressure sags, and your forge loses heat right when you need it. The safe continuous draw in the table above is the rough limit at 60°F - and it roughly halves near freezing. If you are over the line, a bigger tank or a two-tank manifold is the fix, not a hotter regulator setting.
Stop the tank freeze
Your burner needs more vaporization than a small tank can give. Any of these fix it:
30 lb steel propane tank
12 in dia x 24 in
- Weight
- 24 lb
More vaporization headroom than a 20 lb for a hungry burner. Empty weight ~24 lb; must be refilled, not exchanged.
30 lb aluminum propane tank
12.5 in dia x 25 in
- Weight
- 19 lb
Lighter to carry and rust-proof. Costs more up front than steel.
40 lb steel propane tank
12.5 in dia x 29 in
- Weight
- 29 lb
Best single-tank choice for double burners and winter forging. Heavy when full (~69 lb) - plan how you will move it.
40 lb aluminum propane tank
12.5 in dia x 30 in
- Weight
- 24 lb
High vaporization capacity without the steel weight. Premium price.
Two-tank propane manifold (Y-splitter and pigtails)
dual QCC-1 pigtails
Draws from two tanks at once so neither frosts over. The simplest fix when one tank keeps freezing up.
Propane tee manifold with pigtails
brass tee, dual pigtails
Ties two tanks into one supply line. Confirm pigtail fittings match your tank valves (QCC-1).
Complete your gas train
Whatever forge you run, you need a leak-tight hose and adjustable regulator. Leak-test every joint with soapy water before first light.
Propane hose and 0-30 PSI regulator kit
10 ft hose
- Regulator
- 0-30 PSI
Complete gas train for most forges. Leak-test every joint with soapy water before first light.
Propane regulator, hose and gauge kit
8 ft hose
- Regulator
- 0-30 PSI
Includes a pressure gauge so you can set PSI repeatably. Verify the hose is rated for LP gas, not air.
Frequently asked questions
How long does a 20 lb propane tank last in a forge?
At a typical single-burner forging load of about 72,000 BTU/hr effective (90,000 BTU/hr at 80% duty), a full 20 lb tank lasts roughly 6 hours - about three 2-hour sessions. Push welding heat or a double burner and that can drop below 3 hours. Enter your own numbers above for an exact figure.
What is a good propane forge cost per hour?
For hobby forging, anywhere from about $2 to $4.50 per hour is normal, depending on your burner size, how hard you run it, and local propane prices. Above $4.50/hour you are usually running a hungry burner or paying exchange-tank prices - refilling your own tank and tuning your burner both help.
Should I use an exchange tank or refill my own?
Exchange tanks are convenient but are usually filled to about 15 lb, not a full 20 lb, and cost more per pound of propane. If you forge often, owning a tank and refilling it is cheaper and gives you a full fill. This calculator lets you tick "exchange tank" to see the difference.
Does duty cycle really change the cost that much?
Yes. Duty cycle is the share of time your burner is at full pressure. Going from 60% to 100% duty burns two-thirds more gas for the same clock time, so it directly changes both your hours per tank and your cost per hour. Match it honestly to how you work.
Is this an exact engineering figure?
No. These are consensus planning estimates using 21,548 BTU/lb of propane and your inputs. Real consumption depends on burner tune, forge insulation, ambient temperature and how open the forge is. Use it to budget and compare, then follow your forge and regulator manuals.