View Full Version : BTU

April 25, 2010, 11:18 AM
I'm thinking of increasing my WW melting capability. How many BTUs does a burner have to put out to melt a pot of say 50lbs of WW?

April 25, 2010, 12:39 PM
accordin to the wind shields but I`d start at 100,000 Hi pressure burner.

Most burners that are in the turkey fry kits will handle `bout anything the average caster will want .

A 6qt dutch oven full will be close to 150 lbs. easy!

May 7, 2010, 08:52 AM
Many turkey fryers have... um... overly optimistic BTU ratings. If it says its 60,000 BTU and has a tiny 5PSI regulator, you know something is wrong...

But even with that, if you do a few mods like

Move the burner up closer to the pot
Remove/bypass the safety timer
Improve the wind screen
Use a pot that mostly covers the ring/wind screen

Even the smallest turkey fryer will do the job.


May 7, 2010, 08:58 AM

Ya brought out a good point `bout the regulator, I use a fryer that has the adjustable reg.

But remember if ya turn up the heat ya need to watch the temp so not to melt the zinc floaters!

Jumping Frog
May 30, 2010, 08:30 AM
But remember if ya turn up the heat ya need to watch the temp so not to melt the zinc floaters!
Yep. I keep a close eye on the temperature so that I don't melt zinc. If I turned my turkey frier onto full blast with a big pot of wheel weights (my pot holds about 100#), the bottom of the pot will have molten lead well above 850 degrees while the pile of wheel weights on top hasn't even melted yet. That is a major problem because zinc would melt right into the mix.

I turn the heat down so that the pot heats more evenly and gradually and make sure I don't melt any zinc. It is a little slower to melt, but I save a lot of time because I don't bother sorting the wheelweights ahead of time. I just skim off the unmelted zinc and steel weights.

June 1, 2010, 02:48 PM
hangfirew8 Many turkey fryers have... um... overly optimistic BTU ratings. If it says its 60,000 BTU and has a tiny 5PSI regulator, you know something is wrong...

Exactly. I boil crawfish with the same burner (different pot) and it takes a long time to get 50 gallons up to boil (lots of crawsfish). I did some testing on how long it took to boil a gallon of water. I have two burners, one is cast iron rated at 50,000BTU and a jet burner rated at 100,000BTU. The calulations with the time it took to boil was more like 15,000BTU (cast version with 10psi regulator) and 36,000BTU for the jet(with 20PSI regulator. I really comes down to the regulator, becuase both designs can handle the power up to 60PSI regulator.

Home depot has the Jet Burner with a 20PSI regulator for $34.95

this is cheaper than just buying a 20PSI regulator. I try to keep mine turned pretty low to keep from melting any zinc weights i might have missed. I use the 6qt dutch oven and you have to fill, melt, fill, melt and you can get a full 6 gallon bucket of weights melted in one pot.

June 24, 2010, 03:10 PM
Most of those BTU/hr are about speed of the melt. A Lee 10 lb pot has a 500 Watt heating element. 500W=1,706 BTU/hr. If 1,706 BTU/hr will melt 10 lbs in a reasonable time, then 5 times that (8530 BTU/hr) will melt 50 lb in the same reasonable time if the coupling to the heat source is as good. Once hot, because the larger mass has less surface area per unit weight, it will actually take even less to keep it melted. So, the melting can be done with under 10,000 BTU/hr. The rest is gravy for speed.

Boiling water: lbs of water times degrees of temperature rise needed to reach boiling = BTU's, total. 50 gallons is about 417 lbs. If you raise the temperature from 75°F to 212°F, with a BTU raising a pound of water one degree, that will be 417 lbs × 137 degrees difference × 1 BTU/lb-deg, or 57,162 BTU's. So that's how many BTU's you have to put into the water. How long that takes to do depends on how many BTU per hour the heater puts out, + BTU's for heat lost to to the air or never fully put into the pot during the heating. If you suppose the open flame loses a third of its heat to the air, then a 15,000 BTU/hr burner would put about 10,000 BTU/hr into the pot, so it would take 57,162 BTU/10,000 BTU/hr = 5.7162 hr, or five hours and 43 minutes to reach the boiling point.

It won't work out that smoothly, because loss rate to the air increases as the pot heats up, but you get some sort of ballpark idea this way.

June 24, 2010, 11:18 PM
okie pokie unclenick, does any of that mean that a propane stove claiming 60,000 BTUs is capable of melting say 50lbs of WW in a cast iron pot?

June 28, 2010, 01:37 PM
salvadore: short answer, YES, very much so. You will probibly have to turn it down some (half way) to bring the heat up slow enough not to melt any zinc on the bottom before the top of the pile is melted.

June 28, 2010, 04:03 PM
Exactly. You only need maybe 10,000 BTU/hr. 60,000 BTU/hr is overkill, so bring her up nice and slow and watch the temperature. Try to hold it at around 700°F even until you've got all the crud metal skimmed out.

By the way, the burner specs are shorthand. It often simply says BTU's but they mean BTU's per hour. Also, I just noticed Harbor Freight has a sale on their IR thermometer (http://www.harborfreight.com/non-contact-laser-thermometer-96451.html) which covers this range. Not sure how accurate it is off lead, but I know a number of guys are using them on mold blocks.