UKC

With the Ulti, Primus have released their first radiant burner system stove, a model made to perform in the toughest conditions. Robust, fuel-efficient and windproof, this powerful stove boasts an impressive boil time, making it a real contender for expedition use. Finally, a competitor to the MSR Reactor? Dan Bailey seeks to answer this burning question.

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Stove reviews should also state amount of fuel used; boil time is the usual headline figure, but isn't very interesting for real world situations. Whereas fuel used is (see recent thread asking how much fuel would be needed for a trip).

I acknowledge that quoting fuel used with a gas stove can be difficult, because there's a control valve that varies flow rate, and 'up to 11' fast boil for that headline time will be inefficient, and finding the optimum setting for fuel used is difficult. But I would at least like to see fuel use for that headline fast boil.

It's a fair request. Very difficult to achieve with any degree of accuracy, and I wonder how (or if) we'd account for temperature, air pressure etc. But within the limits of my kitchen I could do at least a rough test of the Ulti vs Reactor on full output, simply weighing the canister before and after. I'll try to make time for that in the next few days

620g and £285 for a stove and pot? 

You're not really selling it for me. 

That's essentially the approach I used in my stove-building days; using my kitchen as reference. You need a means to determine 'boiling', too; I would put a loose lid on, and use the point at which a jet of steam emerged: the 'rolling boil' is very subjective. You can also make sure the starting temperature is the same, by using water stored in a fridge.

The MYOG stove-building community seemed to adopt 500ml as a test reference, though the US types did prefer 2 cups (with the added difficulty of the variety of 'US fluid ounce' definitions).

Can you really confirm that? Unless the stove actually has a gas pre‑heat tube, it shouldn't ever be used with the canister inverted, ever.

Unless you fancy big fireballs, that is!

 If it does have one, then that would be its biggest bonus over the Reactor.

So far, the Reactor (while costing even more) was the only commercial gas stove that could easily melt snow or brew a cuppa in gale‑force winds (tested at 40 knots by yours humbly, right at a summit weather station, as coffee is a must, no matter what). If the Primus can do that too, it would be quite a welcome alternative to it. Whether that justifies its price is a different matter, but when there is not really much of any competition...

Unless done in some realistic conditions of freezing and windy, most such kitchen tests are nearly useless and can be even quite misleading. A Jetboil or its Chinese clone might still achieve the fastest time or least fuel consumption in the kitchen, but actually fail to even get the water boiling whenever it's really gusting outside.

Any meaningful test of fuel consumption would require a climate‑controlled wind tunnel, basically.

And most anecdotal tests "in the wind" are nearly useless as well, since hillwalkers don't usually pack anemometers with them, and most people are prone to overestimating local wind speeds by a factor of two (see the recent tent discussion).

I'll never need or buy one of these but well done Primus for the folding legs: I've never been a fan of the tottering towers you see even around normal campsites. For most uses I find the remote cylinder design is far more practical.

Well that's what Primus say, so I suppose it has one of those 

I did once do a test of various tower stoves, in which i tried to replicate wind using a hairdryer. It gave me the results I'd expected from more real-world use. Jetboil poor, Reactor impressive

Thanks for the confirmation! On a second glance, that brass pre‑heat loop is even visible in one of your photos of it. That liquid feed loop might also explain the weight difference.

That should make it quite a bit better in very cold weather than the Reactor, without having to resort to the canister water bath trick. I'd gladly accept the added weight just for that.

Where would one find this 'MYOG stove-building community'?
I was recently mulling making my own stove in some fashion, but had only got as far as youtube research.

Well, I shared a lot of stuff on OutdoorsMagic, but the entire forum & history has been deleted by new owners.

The other, bigger place is the US backpackinglight, which has* a large, active MYOG section, where people make some fantastic stuff (stoves, packs, sleeping bags/quilts, tents. etc.)

* well, it had; I haven't visited in ten years or so...

If both/all stoves are available, then run the tests at the same location and time.

Say in this example, weight the gas cartridge's before the tests (and mark). Do the 0.5 boil test ten times (potentially unscsrew - rescrews the cartridge between every test). And then weight the cartidges again (at home).

You can't compare the results between different tests. But obviously it can give you and idea between the ones on the same test.

And to elaborate it a bit... how about always use the Reactor as a benchmark stove in every test. To sort of tie the different tests together. It's not perfect, but gives a rough idea.

In reply to Frank R.:

The Primus Ulti was recalled due to the inverted canister issue.  

Here is correspondence from Primus relating to the recall:   (Lifted from the Backcountry Skiing Canada youtube channel.)   youtube.com/watch?v=jiTm1H0s9PU&

Thank you for contacting us! We appreciate your trust in and use of Primus products. We want you to know that we always have the customer's needs and safety in mind, therefore we take the situation that has arisen around the Ulti stove very seriously. There were some customers who had problems with their Ulti stove unexpectedly catching fire and we take full responsibility for these unfortunate situations (no one was hurt as far as I know), as we had misleading and insufficient information (especially the pictures) during some sales of Ulti.

I am attaching the latest information we have received about the situation. The stove itself is not faulty and is safe to use while keeping the following instructions and information in mind! For optimal performance with the stove, follow these guidelines: · Always start with the gas canister upright. Never invert it when lighting the stove for the first time. · Warm the gas canister to between 10-20°C before starting. If it's cold outside, store it inside your down jacket for a while. · Choose a dry and stable place for your stove and gas canister. Avoid placing them directly on snow. · Make sure the stove and container are on a stable surface. · Light the stove and let it run for at least 60 seconds with the container upright. This will allow the stove to heat up and get a stable flame.

Keep the canister upright as long as the stove runs smoothly. · If the pressure of the stove drops due to a cold canister or low fuel, then it may be good to invert the canister. This allows liquefied gas to flow through the preheating loop, vaporise and feed the burner. This technique is particularly useful in very cold conditions (down to -20°C) when using Primus Winter Power Gas. · To minimise the risk of flashback, do not use gas with a propane and butane mix. Instead, use gas with a propane and isobutane mix such as Primus Power Gas and Primus Winter Gas.

"I am reaching out to inform you that we have recently identified a potential issue where a small number of Ulti stove systems have experienced flashbacks when used in a certain way and with specific types of fuel. While this has only affected a limited number of units, with no injuries for the 6 reported cases, we are taking proactive measures to ensure safety and optimal performance when using our product. A flashback in a gas burner is a combustion problem where the flame burns inside the burner instead of at the burner top where it should be. This can lead to inefficient combustion, damage to the burner, and, in the worst case, safety hazards. We have found that the flashback issues occur when starting the stove with the gas canister upside down, using a fuel with butane in the mix.

The Ulti stove system is capable of operating with the gas canister in an inverted position, which is particularly useful in extreme cold conditions. However, this should not be considered the standard way to use the stove. The canister should only be inverted when normal upright use is not possible, such as in very cold temperatures or when insufficient pressure is present in the canister. To minimize the risk of flashback, we strongly recommend the Ulti stove system to be used with Primus Power Gas and Primus Winter Gas canisters. These fuel types contain a propane and isobutane mixture, which is what the Ulti stove is designed to work with.

By using Primus Power Gas or Primus Winter Gas and following the correct canister positioning method, we are confident that the Ulti stove system will continue to perform safely and efficiently. To ensure all users are well-informed, we will do the following: For all not yet produced products and the ones we have on stock, we are updating our CE safety label and product manuals to reflect this fuel usage guidance and the proper inverted canister instructions. A safety card summarizing this information will also be attached to the stove's valve for easy reference. For all delivered products until February 14th, 2025. We will create, produce and send out to you an instruction with the following information to insert in the packaging of the products:

Thanks. But frankly, the people having issues might have just been doing it wrong in the first place...

It's still nice of Primus to reply and recall, though, even if IMO a recall is not really needed.

Basically, all stoves with a pre‑heat loop require the very same certain care procedure:

1. prime it and fire it up from the upright canister position and let it burn for a while to heat up the pre‑heat loop, or use the water bath canister trick as well, or just warm up the canister on your body.
2. only then can you ever invert the canister for liquid feed, as otherwise you risk the stove flaring up heavily.
3. After heating the pre‑heat loop, you can finally invert the canister for reliable liquid feed.

Not doing all the steps is just asking for trouble of the fireball kind...

It's odd and a great shame that the didn't just take the existing Primus Lite + stove and give it a preheat tube and feet, plus a gas supply hose to allow remote canister (inverted if needed). Called it Primus Lite Remote, or something

I'm sure they could have made something much much cheaper and lighter than this expensive and heavy stove, all with very low development costs. I think they missed a trick!

For me, this is a step backward from the MSR Reactor.

The Primus manages to be both heavier and bulkier.  

The only advantages are the lower center of gravity and the inverted feed ability.

For me, I've never tipped over my Reactor, so the lower center of gravity is not an issue.  When using on uneven surfaces, I can use a hanging kit with my Reactor.  As for the inverted feed, I've found that the warm water bath works well with the Reactor, and the addition of a titanium bowl to the kit adds so little weight that the Reactor plus a titanium bowl still weighs less than the Primus.

To get my attention, the Primus would need to be lighter and pack down smaller than the Reactor.  As long as it's heavier and bulkier, I'm not going to be interested.  

Reactor still has a few issues from becoming the perfect cold weather gas stove. Like having to work around its limitations of not having a liquid feed, or its permanent shutoff valve (even if it had likely failed only in about 1% of cases or less).

As esoteric as it already is (in the world littered with cheap Jetboil clones), it's always been a one off. It's really nice to see some potential competition to it, possibly even done better.

After all, no one ever regularly using it was ever concerned about weight over their already utterly UL Chinese 35g gas stove, or even lighter meths burner. Hexamine would have been the lightest, actually, but sometimes you just need or want something else.

We just want to melt snow or boil water, fast, out in the wind. Period. That now two companies seem to try to cater to that very special niche sounds really nice to me.

Also, by my reckoning of liquid feed stoves, the Primus could be still easily usable at -20℃ or less, where the Reactor would struggle. That would have to get tested of course, but the physics of liquid feed stoves work out. Even the 200 g of added weight is not really an issue if it means that your stove is actually working at below -20℃, or not working at all. Even if you still have to prime it with a warmed‑up canister.

Even with its pretty ingenious gas flow regulator, there is only so much the Reactor can do when entropy kicks in. And pretty much everybody actually using it routinely had really wanted a version with a liquid feed, even after using all the tricks out there like the water bath or else. Hence all the Moulder strip "Alpine bombs"...

My Reactor is one of the original models, without the safety shut off.  The safety shut off is a stupid design feature.  

The Fire Maple Mars is another entry into the radiant burner category.  Remote canister.  No pre-heat/inverted capability however.  

I also like the competition.  However, I think that Primus missed the mark.  The target user group for this type of stove is climbers who need to melt snow.  Climbers care a lot about weight and bulk.  I would have been much more interested in a competitive stove that cut weight from the Reactor, even if it was at the cost of some BTU's.  

I have used my reactor at -30C without issues.  Warm the canister under my coat, use the first few ounces of hot water to make a warm water bath.  Works fine.  Can even use it in hanging configuration this way.  I too am one of those who has wished for an inverted canister Reactor, but that feature does not offset the weight penalty in my book.  

See the photo of my cold weather Reactor solution.  It adds just under 2 ounces to the Reactor, and can serve double duty as a bowl for eating, scooping snow, etc.  

Doesn't MSR make a remote feed hose now? Though I suppose if the Reactor doesn't have a pre-heating pipe maybe inverting a canister wouldn't help much (or be sensible?)

This is my biggest regret buying the Pocket Rocket Deluxe, remote canister just seems to make so much more sense in terms of practicality and safety.

MSR do sell an adapter which seemingly converts any stove into a remote canister one but I think the price is a bit steep for what it is. Checking now it seems like its only £28 compared to the £45 when I last looked. Tempted now..

https://ultralightoutdoorgear.co.uk/lowdown-remote-stove-adapter/

I've had the same experience with my MSR reactor.  One time I was on a wild camp with several others and the tents were in a sheltered but still quite windy spot.  Some couldn't even light their stoves or keep them lit, others were getting no-where due to the wind related heat loss.  I ended up providing boiling water for everyone's dinner and hot drinks via my Reactor.  It's been a solid, reliable piece of kit and they can be picked up on ebay at good prices if you're patient. 

I have cooked pasta using my Reactor so it's not totally hopeless for basic cooking, but I've mostly used it for boiling water.