This page discusses some topics on propane burners that are most often used by homebrewers. There are basically two types of burner but each type has a few variations.
Propane Burner Types
One type is called a cast iron burner and is the type you would find in the bottom of a water heater.
A variation of these burners is the 6" or 10" Hurricane or Banjo burner which put out a lot more heat over a wider surface.
Then there are the jet burners which have advertised BTU ratings that are through the roof (as high as 880,000 BTUs). Which one you choose depends on your brewing set-up and your budget.
Homebrewers often have more difficulty with their propane burners when designing and building a RIMS system than any other problem. I suggest you do the calculations, take a look at other brewer's systems, and do a lot of research before deciding on which one is right for you and your system. Don't be one of those guys that always thinks "bigger is better". You may find a small BTU cast iron burner is perfect for your system and will be much more cost effective as well. Before we discuss the burners, here is a little background on what a BTU rating means.
A BTU (British Thermal Unit) is the amount of energy required to raise 1 lb of water (.12 gallons or 0.454 kg) of water 1 °F (0.556 °C). In North America, the term "BTU" is used to describe the heat value (energy content) of fuels, and also to describe the power of heating and cooling systems, such as furnaces, stoves, propane burners, barbecue grills, and air conditioners. When used as a unit of power, BTU per hour (BTU/h) is the correct unit, though this is often abbreviated to just "BTU".
Here is an easy way to see how many BTU's you will need for your pot size. Water density is 8.3 lb/gal. To raise 1 gallon of water (1 x 8.3 = 8.3 lbs or 1 x 3.765 kg = 3.765 kg) from 70°F to 212°F (21.11°C to 100°C) in 1 hour you will need 8.3 lbs (3.765 kg) x 142 = 1,178.6 BTUs. Using this BTU requirement for each gallon of water you can figure out how many BTUs would be required to boil your pot of water in one hour. For example a 62 quart pot (15.5 gallons) (full of water) would require 15.5 X 1,178.6 BTUs = 18,268.3 BTUs to bring the pot to a boil in one hour, assuming 100% efficiency.
Of course 100% efficiency isn't realistic. Assuming 100% efficiency, a 54,000 BTU/hr cast burner should bring that pot to a boil in 18,268.3 / 54,000 BTUs = .3383 hours or 20.3 minutes. Anyone that has ever tried to bring a full 62 quart pot to a rolling boil knows that it doesn't happen that quickly.
How Much Propane Does Your Burner Use?
Another way of looking at this is "how much propane will my propane burner use?" The BTU rating (really BTU/hr) takes the pressure and volume of the burner into account, putting all burners on the same "units" if you will.
Assume you have 20 lbs of propane in your tank (many 20# tanks only hole about 17 lbs of propane). A pound of propane has 21,591 btu/hr fuel value, so a 20# tank has 20# x 21,591btu/# = 431,820 btu available.
If your burner is rated at 40,000 BTU (same as BTU/hr), then 431,820 btu ÷ 40,000 btu/hr = 10.8 hrs. This is how long your propane tank will last at full throttle. Compare that with a 160,000 BTU/hr burner which should only be able to run appx. 2.7 hrs on the same amount of propane.
Of course most of us don't run our burners at full throttle the whole time, so the tank should last longer than these numbers would indicate.
Much heat is lost before it gets to the pot, and how much is difficult to calculate. Outside temperature and wind each can negatively impact the efficiency of the heat transfer from the flames to the pot. A safe estimate would be 50% efficiency, so doubling the heating time would probably be more realistic.
Evaporation takes away heat and to maintain a rolling boil will require the input of additional heat besides that required to raise it to a boil. To boil away, or evaporate 1 pound (.454 kg) of water in one hour would require approximately 1000 BTUs (One pound of steam contains 970.1 BTUs and this is the amount if energy needed to evaporate 1 lb. (0.454 kg) of water in one hour beginning at 212°F (100°C). (taken from steam table)
So, a 54,000 BTU burner should easily boil a 62 quart pot in about 41 minutes (assuming the 50% efficiency) and hold that pot at a rolling boil.
Kettle Size Considerations
However, if you move to a 104 quart pot (26 gallons), the heating time almost doubles and now you are sitting around an hour or more waiting for the pot to boil.
When boiling these large volumes of water, you may want to consider moving up to a higher BTU propane burner. A 110,000 BTU burner would approximately cut these boil times in half.
Cast iron propane burners are best suited for pots that are below 40 quarts and jet burners are best suited for pots above 40 quarts if you are concerned about boil times.
But there are other considerations to think about besides boil times. A cast iron burner has a maximum output of around 54,000 BTUs but has a much more diffuse flame pattern which spreads the heat more evenly across the bottom of your pot. You are less likely to caramelize your wort with a cast iron burner but you will have to wait longer for it to boil.
A jet burner mixes the propane and air in a venturi tube an can produce a single "jet" flame which can be very intense in a localized area of your pot but can generate around 110,000 BTUs. The drawback for a jet burner is caramelization and darkening of your wort, which may not be a problem if you are brewing a barleywine or doppelbock, but can be a big problem if you are brewing a Kolsch or Pilsner.
Other burners are now available for use by homebrewers. One of the most popular is the Hurricane (or banjo) burner which as a stated BTU power of 210,000 BTUs when used with a high pressure regulator.
Use Caution When Comparing Stated BTU Values
One supplier states that it can put out 60,000 BTUs at less than 1 psi when using a low pressure regulator. This will not only save you propane, it can also save you from caramelizing your wort.
Always be cautious of stated or advertised BTU ratings when shopping around for a new propane burner. For my RIMS setup, I chose a Hurricane Products 10" Low Pressure Propane Burner, primarily because I chose to use Honeywell dual valve gas valves which require low pressure input of propane to work. I am pleased with the burners output however and these burners are available at most homebrew supply stores.
Problems Associated with Jet Burners
There are propane burners available which have multiple jets attached to a cast iron ring. This should solve the problem of scorching your wort somewhat, due to the wider dispersion pattern of the flames but I have heard that these burners are difficult to use due to their cheap workmanship and materials. Some brewers must remove each jet and seal the threads with an engine sealant such as Permatex to keep the burners from leaking and producing a lot of yellow flames.
They are, however, rated at around 175,000 BTUs for the 9"/23 jet model.
Other problems often associated with this kind of propane burner are the lack of adjustability of air intake and the difficulty getting your propane delivery set-up to adequately supply the amount of fuel needed for all 23 jets.
Some brewers have plugged many of the jets (those that face each other and create hot spots) to alleviate the problem of lack of supply pressure. They often say they'd buy the 10 jet model if it was more widely available. (I found one site called Tejassmokers.com which carries models with 32, 44, and believe it or not, 88 jets which is purported to put out 880,000 BTUs of heat. Can you imagine trying to seal the leaks on that many jets, or trying to supply enough propane to keep the propane burner burning with a nice blue flame).
There isn't much you can do about the lack of air adjustment on these kinds of burners. It is described as an "On/Off" or "all or none" type burner. For the concave bottoms of converted kegs, if you mount the burners too close to the pot, you can sometimes get an oxygen depleted area, depending on your wind shield design, which produces a lot of yellow flames as well. To solve this problem, mount your multi-jet burners further away from the bottom of a converted keggle, or design your wind shields so that they can get adequate flow of fresh air for the venturi intakes on each jet.
Whichever burner you choose, try to buy one from your local homebrew supply store first. Supporting those that support you is always a good idea. There are many options available on the internet however and many good vendors as well.
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References: Information for this article on Propane Burners was taken from http://www.lalagniappe.com/mall/lobbycookerfaq.htm, http://en.wikipedia.org/wiki/British_thermal_unit , the steam tables at http://www.efunda.com/materials/water/steamtable_sat.cfm, http://gashosesandregulators.com/propaneregulatorfacts.html, and a lot of helpful information was adapted from threads on HomeBrewTalk.com.
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