QuietStove Burner Cap for XGK-EX

The QuietStove burner caps are intended as a replacement for the burner flame spreader plate on stoves having the “roarer” style burner, such as the MSR XGK and Dragonfly, Svea 123 and 123R and similar Primus 71 and Optimus stoves. These stoves are famous (notorious, some would say) for the loudness when turned up full blast. The XGK, for example, is said to have two settings — 747 takeoff and “launch the Shuttle”. Simmering on these stoves is tricky, at the very least. QuietStove claims a major reduction of the sound level and increased simmering capability, along with a faster boil time and faster cooking.

[UPDATE 9/4/2013 - Quietstove has reduced the cost of their line by about 40%, to $89 for the XGK-EX version. While this partially mitigates the "Cons", it still means that at $159 (REI price for the XGK) plus the $89 for the Quietstove Cap, you are spending close to $250 vs an MSR Whisperlite Universal, which is just as quiet and faster in boil time, at $140 at REI, or more than 75% greater total investment - though this is better than doubling your investment. This might justify raising the rating to 3 stars, though the other "cons" remain unchanged]

The significant reduction in noise level and improved simmering capability, as supported during my tests, would have led me to rate the QuietStove at a full 5 stars. However, the significantly longer boil time, along with the high price and other points listed below in the “Cons” section, led me to give a 2.5-star rating, which may even be a bit generous.

Background: When I was very young, the ranch house we spent part of the year had a kerosene stove (Perfection brand, a very common one in the rural Southwest). It was silent and smelly, plus those “Perfection” stoves had a reputation for being the cause of many house fires (not ours, thanks to very strict rules by my parents on the stove usage). In my teens, when I started climbing and backpacking seriously, I bought myself a Primus 71L — small, lightweight, self-priming, noisy, and marginal for simmering. Since that time, my household has accumulated close to 30 stoves, a combination of alcohol, Esbit and similar tablet, compressed gas (butane, propane, and mixed gases), white gas, kerosene, wood, and multifuel stoves. Each has its strengths and each has its weaknesses.

My primary stoves for expeditions and backcountry are currently the MSR XGK-EX, MSR Simmerlite (discontinued by MSR in 2012), and Jetboil Helios. The XGK-EX is the third generation of XGK I have owned (still have and use my XGK-II). All have proven dependable in conditions from Death Valley in summer to winter in the Sierra to harsh conditions in Antarctica and on Denali (the Helios was not used in Antarctic or Alaskan conditions, though).

The XGK is my primary stove — dependable, works anywhere, durable despite rough handling, and fast-cooking. However, it is extremely loud, measuring 85 to 86 dBA at 30 cm. This level requires earplugs or protective headphones. According to OSHA recommendations, a sound level of 90 dBA requires ear protection and time restriction. At 90 dBA, the maximum duration without ear protection is 8 hours per day. This is louder than a full orchestra (though much less than the typical rock concert level).

The decibel scale is a logarithmic one, so that a change of 10 dB is a change of a factor of 10 in sound pressure. For many of us, getting into the woods and hills is in part a quest for an escape from the noises of the urban environment for the sounds of birds singing and babbling brooks. The loud sounds of a roaring stove are an intrusion on that silence.

There are two major burner designs used in backpacking and mountaineering stoves, the roarer burner and the silent burner. Both the roarer and silent burner designs have been around since the late 19th century (Franz Wilhelm Lindqvist invented the original Primus in 1892 as a significant improvement over the felt wick burners of the time). The roarer burner is recognizable by the upside-down “bell” topped by a “spreader plate”, while the silent burner is characterized by a wider disc or cylindrically shaped  top with many small holes or a mesh screen around the edges.

Liquid fuel and compressed gas stoves are available with both types of burners, though most compressed gas stoves use the silent burner design. As the name implies, the roarer burner is very loud. The “silent” burner is less loud, but is still noticeable at some distance away. Various approaches to reducing the noise level have been tried over the years.

The approach of the QuietStove is in effect a conversion of a roarer burner into a silent burner. Caps like the QuietStove burner cap have been around for a while, with several other brands available, such as the Dragon Tamer (originally designed for the MSR Dragonfly). Many years ago, Optimus had a conversion for one of its stoves that was very similar to these caps, that I have been told was the inspiration for the Dragon Tamer.

How do you choose between the roarer and silent burner designs? They can be designed to perform the same in heat output and fuel efficiency. One obvious difference is that the roarer burner, as the name implies, is significantly louder than the silent burner design, even in a small stove like the Svea 123 or Primus 71L.

Another difference, usually discovered by accident, is that if you spill or boil over the soup or otherwise get liquids on the burner, the roarer burner is easily cleaned and re-lit, while fluid getting into the screen or waffle-plates of a silent burner is very difficult to clean, even if it is just water. This is one reason for the waffle-plate design used in the MSR Whisperlite and some of the Coleman Peak 1 stoves – the plates can be removed with a single screw and separated to be wiped clean and dry. For water spills (or leaving the stove in the rain), the roarer burner is readily dried and back to cooking by following the usual priming process, perhaps with a little extra priming fuel.

If the spill is a soup, it is cleaned of spills by simply popping the burner plate off, wiping clean, using a cleaning needle (or shaking the shaker jet style), and lighting as usual. Roarer burners are also somewhat less sensitive to wind than silent burners and are usually somewhat more efficient in fuel usage. In short, the roarer burner is more easily maintained and more “bomb-proof” than the silent burner, the reason that stoves like the XGK and Primus Omni are preferred for expeditions.

Details: When Trailspace’s Chief of Gear Reviews, Seth, was looking for someone to test the QuietStove cap, he needed someone who had one of the stoves for which the caps are made and had access to a sound meter. Thanks to my years as a university professor, teaching physics courses, I have such a calibrated device, plus I have several of the stoves for which models of the QuietStove cap are currently available.

QuietStove is a fairly new company, with models for a limited, but growing, number of stoves available. The XGK being the stove reputed to be the loudest of the backpacking stoves, this was the one I chose, but included sound measurements on a couple of other stoves for comparison un-muffled.

Two major questions need to be examined with this device, in addition to the usual questions about any gear, I wanted to know: “is the sound reduction significant?” and “what is the effect on cooking/boiling time?”

On their website, QuietStove claims that “The QuietStove will make your stove approximately twice as quiet (-10db difference). In our tests water boil times can be up to 10% faster.”

I will note that MSR’s stance is that conversions and alterations of their stoves are “not recommended”. In a discussion with their tech support people, they expressed much the same reservations as I found during the testing.

On receiving the large box from UPS, I opened it to find a huge amount of Styrofoam “peanuts”. This kind of overpackaging is all-too-common without regard for the environment these days. The cap itself weighs 49 grams/1.75 ounces per my calibrated electronic scale. The upper part of the cylinder measures 1.5 inches/38.1 mm in diameter (1.635 in/41.55 mm for the “skirt”), per my electronic micrometer.

When I placed the cap in the bell of the burner, I discovered that either (or both) the “skirt” or the bell of the XGK itself are not quite perfectly round. Measurement of the skirt at several places found a largest diameter of 41.63 mm, just a tad less than 0.1mm out of round. This meant that the cap could be slightly rocked back and forth. I do not think this “out of round” made a significant difference in performance, though my years in science and the aerospace industry did cause a bit of worry. 

I will also note that the website states that the cap is made of stainless steel. The first image, which is next to a ColorChecker standard white balance card shows a distinctly “non-stainless” color, indicating that the cap has some type of coating or plating (probably a powder-coat paint). After the first firing, the color changed as shown in the second image.

Installing the cap is done by removing the burner spreader plate and placing the cap in the “bell” with the arrow pointing toward the fuel line entry point to the jet (the arrow is slightly off in this photo, but was correct during the tests).

Since the weight of the cap struck me as rather heavy, I weighed my XGK and its accessories as they would be carried in my backpack, 17 ¾ ounces. The cap thus weighs 10 percent as much as the XGK-EX. The cap replaces the burner spreader plate, which is negligible in weight, so using the QuietBurner cap would effectively add 10 percent to the weight of the stove (you might want to keep the burner spreader plate with you in case of losing the loosely fit cap).

I will also note that QuietStove indicates on their website and in the very brief instruction sheet that the expansion of the bell with heating and subsequent contraction can make the cap fit tightly, requiring large pliers to remove it if needed (although it took a small effort to remove the cap after cooling, I did not find this to be a significant problem with large slip-joint pliers). This too, would add extra weight (your largest Leatherman would not be up to the task).

CAUTION!!! Do NOT attempt to remove the cap until the stove has completely cooled! The large mass of the cap, which helps with its performance, holds heat for a very long time, and could severely burn you if you did not wait until it had completely cooled (10 min or more after being used for cooking).

The test setup was on my back sandstone patio, as in the image below:

The microphone of the sound meter is positioned just above the height of the windscreen, 30 cm from the center of the burner, and transverse to the direction to the burner, per the instructions for use of the meter. This arrangement was used for all burns of the stove with the standard burner spreader plate and with the QuietStove cap in place, with and without the pot of water to be boiled. Since we are concerned with the sound as it is perceived by the human ear, the meter was set in the “human” A-scale, slow response setting (the C-scale, which has a constant response across the spectrum, responds differently than the ear perceives the sound).

We have been having unseasonably warm weather for early fall (late September) here in the SFBay Area. The air temperature during the testing mid day was 73 to 75 deg F, with a light wind (2 to 4 knots). I would have expected a somewhat shorter boil time because of the higher temperatures, but did not find that to be the case.

I first measured the sound level of the standard XGK-EX to provide a baseline at 85 dBA. I also measured the sound level of two other MSR stoves which are considered significantly quieter than the XGK for comparison – my 20 year old Whisperlite International (68 dBA) and my 10 year old Simmerlite (69 dBA), -17 and -16 dBA respectively compared to the bare XGK-EX, or at the level of a typical conversation. 

I next installed the cap in the XGK-EX and measured the sound level at 68 dBA, the same as the Whisperlite. This 17dBA reduction in sound level (a factor of 50) is indeed huge, and is greater than QuietStove’s claim of -10 dBA. Having done the test runs consecutively (and repeated them several times), I was fairly impressed.

However, the reduction was really no surprise, since the cap is, in effect, a conversion from the “roarer burner” design to the “silent burner” design. The close match to the Whisperlite and the Simmerlite is also to be expected, since those stoves are both “silent burner” designs. The Whisperlite is the “waffle-plate” style, while the Simmerlite is the “screen” style.

Lighting the stove with the QuietStove cap in place is a bit different from the normal lighting procedure for white gas and kerosene stoves with the usual roarer and silent burners. With the traditional burner designs, a tiny amount of a priming fuel is placed in the priming cup and lit. The priming fuel may be the stove’s normal fuel (white gas or kerosene) or alcohol. No matter which variation of priming, it is important to NOT overprime with an excess of priming fuel. If your priming flame is more than 3 inches above the burner, you have overprimed — reduce the amount of priming fuel next time.

Getting the priming fuel in the cup may be done by any of several means. The Svea 123, for example, can be held cupped in your hands to produce a slight warming and pressurization, the valve opened, and the fuel is forced out to dribble into the indentation in the top of the attached fuel tank. Or a small amount of fuel may be placed in the cup with an eye dropper. With pressurized stoves, such as the XGK, the fuel tank is pressurized by a pump, then the fuel valve opened slightly then closed to allow a tiny amount of fuel to run into the fuel cup (do not confuse the overflow cup with the fuel cup – that guarantees overpriming).

Some people prefer to use a paste like FireGel. Whichever means is used, the primer is allowed to burn until it is almost out, and the fuel valve quickly turned on to produce a clean blue flame. The QuietStove cap differs in one major respect – the valve is left completely closed until the priming fuel is completely burned out. Then the fuel valve is opened and the stove is lit at the holes in the burner cap.

It is extremely important to make sure that the fuel is NOT lit under the cap where the fuel vapor is exiting the jet, a condition QuietStove refers to as “under-burning”. In this case, the fuel is burning inside the cap. This may overheat the cap until it is glowing orange.

I noted in the videos on the QuietStove website and in several YouTube videos that everyone was using the extended gas lighters, usually used for lighting charcoal or gas-fired fireplaces. No one used matches or Bic-style lighters. The reason for using such lighters is (1) to be certain that the vapors are lit at the holes in the burner cap and (2) to avoid getting your hands too close to the burner, since the vapors light with a “poof!”, with the likelihood of at least singeing the hair on your hands.

I also used an extended piezo lighter, though it did not work as well as the extended gas flame. The need for using an extended lighting device will add still more weight to what you need to carry with your stove. This need, plus the “under-burn” problem, are two of the reasons I downgraded my rating of the QuietStove to 2.5 stars.

Turning to QuietStove’s other claim, a reduction in boil times, I heated a liter of water to boiling with and without the cap, in a GSI anodized aluminum pot. The air temperature during the tests was in the 73° to 79°F range, with wind speed 2-4 kts. Water temperature was in the 73° to 76°F range (23° to 25°C). Due to the order in which the tests were run, the runs with the cap in place were at the warmer end of the range. This should have given the QuietStove a slight advantage (shorter boil times), but did not do so.

For each run, the fuel bottle was filled to the same level and pumped the same number of strokes (30 strokes). Once lit, the stove was allowed to run for 5 minutes to reach full operating temperature, and the pump given an additional 10 strokes.

The reason for the extra pumping is that as the fuel is consumed, the air pocket expands, dropping the fuel tank pressure (as we all learned in high school chemistry and physics courses). The drop in pressure is seen as a gradual drop in the flame at the burner, more rapid at first when the air pocket is smallest and expanding by a larger percentage with the usage of fuel.  

Nearing a boil:

The resulting boil times for the unmodified XGK-EX averaged 3m40s, with a full rolling boil at 4m11s. With the QuietStove cap in place, boil times averaged 4m37s, with a full rolling boil at 5m12s.

Since the QuietStove website claims a decrease in boil times, I ran several tests, letting the pot and stove cool between runs until they were cool to the touch. The boil times with the cap in place were consistently longer. I will note that boil times with my Whisperlite and Simmerlite are about the same as with the XGK-EX.

I should also note that the cooling time once you shut the stove off is quite long, especially for the cap. There is enough metal in the cap, hence thermal inertia, that the cap remains too hot to touch (even for my calloused fingers) for 5 to 10 minutes after the stove is shut down.

Since the cap effectively changes the XGK-EX into a silent burner stove, I tested the spill clogging by immersing the cap in water, then seeing how long it would take to drain. The holes are the diameter of a thin sewing needle, thus giving water’s strong surface tension a good chance to work. The result was that I had to heat the cap for a while to get the water evaporated out, something that would happen during the priming process for water, but would be a problem with many soups. You also would not want to drop the cap in the dirt or leave it exposed to blowing dust.

QuietStove does say that clogs can be cleared by inserting anything small enough in the holes to clear them (that is 255 holes in 3 groups of 5x17 plus 4 holes inside the under-cap cavity). I found a very thin sewing needle to be the right size, though it did not clear the water from the holes.

I have several safety worries about the QuietStove and similar devices. One, stemming from the longer boil times, is the potential effect on the carbon monoxide production. I do not have a CO monitor, so I am only extrapolating from discussions in the past few years about CO from backpacking stoves. Since the pressure in the fuel bottle and the valve open to the same full position was the same with and without the cap, I suspect that the flame may be at a somewhat lower temperature, which may result in less complete combustion, and hence more CO. A second question is whether this modification could result in overheating of parts of the XGK, hence perhaps weakening the pot supports.

Conclusions: The QuietStove burner cap does reduce the sound level from the XGK-EX by a significant amount, even more than the manufacturer’s claim. If you already have an MSR XGK-EX or one of the other stoves for which QuietStove makes a cap, and want to quiet the noise, this may be what you are looking for, if the other considerations do not outweigh your desire for a quieter stove.

However, the cap adds about 10 percent to the weight you will carry, plus the need for an extended lighting device and perhaps a suitable set of pliers to remove the cap. Boil time is significantly increased, contrary to the manufacturer’s claim. Although I did not run fuel consumption tests, my impression is that the fuel flow rate at full power is the same for both the bare XGK and the XGK with the cap installed, so that the longer time to boil is likely to result in higher fuel consumption during cooking. The controllability and increased simmering capability may counter this, however, if you do more “gourmet” cooking.

To me, a major negative is that the price of the QuietStove cap is as much or more than a good quality “silent burner” stove that provides a similar noise level ($149 MSRP for the cap vs $139 for a WhisperLite Universal at REI, or $119 introductory price vs $99.95 for the WhisperLite International at REI). In other words, you can get the same reduced sound level with no reduction in boil/cooking time at a significantly lower cost and lower carrying weight.

For example, a Whisperlite will achieve the same sound level with no increase in boil time over the unmodified XGK-EX. For the same or lower price, you could add a second stove, or just buy the silent burner stove in the first place. Alternatively, if your cooking is limited to 3 seasons, a compressed gas stove that screws on top of the canister will have the same boil times with simmering capability, lower sound levels and lower weight, though a higher fuel cost long term.

The bottom line question we always ask in these Gear Review Corps reviews is "Would you recommend this item to a friend?" In this case, my answer is "No, there are better alternatives, and at lower cost."

UPDATE 9/4/2013:

Quietstove's price drop to $89 partially mitigates the price drawback, though it still leaves the total investment of XGK EX plus Quietstove Cap at 77% higher total investment than the MSR Whisperlite Universal, a stove by the same company (MSR), that is just as quiet, lighter than the combination of XGK and Quietstove Cap, and without the penalties of slower boil time and fiddly lighting procedure, but the added feature of being able to use compressed gas in addition to white gas, kerosene, and their near relatives.