Heat Exchange Stove Shootout: Part 3Heat Exchanger Stoves

[Addie Bedford]

Companion forum thread to:

Heat Exchange Stove Shootout: Part 3
Heat Exchanger Stoves

[Michael Ray]

Just fired up my new Windpro for the first time and was surprised (in a bad way) by the results. I just want to verify if this is normal or not. I tried boiling 3 quarts of water and didn't reach a boil after 20 minutes.

Water was a little below room temp (out of the tap but I melted a tray of ice cubes in it to cool it further). Outside temp is about 78 F. Slightly breezy (10 mph). I used the windscreen with about 1/4" gap around the pot. I added maybe 10 small holes (paper punch) along the bottom so air could get in since the standard cutout they provide will be non-existent on smaller pots though about a 3/4" slit still remained. I did not use the heat deflector on the ground (concrete in this case) – I don't imagine I'd ever use it. Pot is just under 8" dia, fairly thin AL.

I had a few bubbles start at 7 min and then some steam at about 13-14, but never a boil. I'm at 600' ASL. The only 2 things I can think of are:
1) Losing too much heat from the pot itself to the breeze as I had purposely left the lid off also so I'd get a worst case baseline and could easily see when things occurred.
2) Not enough airflow. Either need more holes on the bottom and/or more gap around the pot.

I should also note, I wasn't sure how far to open the valve for max output. It was about 1/2 turn for about the first 7 min and then 3/4 turn after that. From what I could see through the slit and the pitch of the flame I could hear, it made no difference once I got past 3/4 turn so I left it there. Went through 48 g of fuel in the 20+ min.

[Roger Caffin]

Hi Michael

Well, 3 qt is a lot of water to heat in one go, and I do have some comments.

First of all, watch out for pot diameter. If the pot has a very large diameter you run a risk of reflecting too much heat back down onto the fuel canister, which can be extremely dangerous. We prefer to not lose readers to this sort of thing… I would say that 8" is getting a bit large, but should be OK. Using a windshield (as you did) does prevent this problem.

With an 8" pot with no lid and a moderate wind, it is quite possible that you had reached the point where evaporation was killing you. I find that using a lid and a windscreen can *literally halve* the amount of fuel used.

I don't think there would have been a lack of airflow. You would have seen a lot of yellow in the flames if this had been the case.

Another problem which I suspect may have happened was that the gas in the canister may have chilled down over the long time you were running the stove. When this happens the stove power starts to fall. Combine that with the possibility that you didn't have the stove turned right up at the start, and a very long boil time will happen.

48 g of fuel is a bit more than I would calculate for 3 qt, but very consistent with the idea that you were losing out to evaporation at the end. Use a lid!

Hope this helps.
Cheers

[Michael Ray]

I'd never boil without a lid normally, of course. Just curious to see what worst case would be. It was plenty hot for freezer bag meals and likely had been after maybe 10-12 min. I should have seen if I had a thermo I could have put in.

Anyway, I didn't know even with remotes you can get the canister too hot so it's nice to know that now though I'll always use a windscreen as well.

The canister was cold. The hose on the Windpro doesn't make it easy to flip the canister either unless you have a decent amount of water already sitting on the stove and return the canister right side up before removing the pot. I've thought about loosening the fitting and turning it about 90 degrees.

I did slowly flip the canister over for a while just to see how the stove would react. While I didn't observe the flame through the slit (it was challenge enough trying to get the canister into a position where it would stay inverted as I didn't have anything to lean it against), I did notice the sound pitch of the flame changed while it was inverted (~30 s) and returned to what it had been when the canister was returned upright. I hadn't expected that. I assume it must be a pressure difference in liquid vs gas feed?

[Roger Caffin]

Hi Michael

> Just curious to see what worst case would be.
In the name of Science … Interesting.

> you can get the canister too hot
Read our article on Exploding Canisters! Oh yes….
http://www.backpackinglight.com/cgi-bin/backpackinglight/exploding_gas_canisters_the_hazard_of_overheating.html

> The hose on the Windpro doesn't make it easy to flip the canister
Very true. Yes, many of us do rotate the connection a bit so the canister can be flipped.

> I did notice the sound pitch of the flame changed while it was inverted (~30 s) and
> returned to what it had been when the canister was returned upright
The power probably increased while it was inverted. Yes, if you want to run for long periods then inverting the canister will solve the freezing down problem. You can also get some boost by putting the canister in a bowl of *cool* (NOT HOT!) water.

It isn't so much a difference in pressure as a reduction in pressure drop along the fuel line. The fuel line does put some drag on gas flow. Same effect of course.

Cheers

[Michael Ray]

> In the name of Science … Interesting.

I'm an engineer so I like to play. ;)

> Read our article on Exploding Canisters!

I knew uprights had this issue but figured remotes were far enough away from significant heat to be an issue.

> Yes, many of us do rotate the connection a bit so the canister can be flipped.

Do you reseal the fitting with something? It appears they have some type of epoxy in the threads. For natural gas piping in the US, they use what is called pipe dope (a gray slimy substance that never hardens), but I didn't know if the threads used here have the same characteristics where that would work.

[Tad Englund]

Michael, I just wanted to emphasize what Roger said about rotating the canister-

You mentioned “The hose on the Windpro doesn't make it easy to flip the canister”

Yes, the hose makes it difficult to rotate the canister unless there is water in the pot. If you don’t rotate the canister fitting on the hose, you are just twisting the hose like a spring, causing tension and the canister or the stove will flip (probably and the most inconvenient time).

To fix this problem- you rotate the fitting for the canister independent of the hose. To do this, grasp the canister while firmly holding the hose and then turn either the canister or the hose. It will put up some resistance but it will turn. I leave the canister attached so I can tell, where exactly I need to rotate the fitting on the hose, to get the canister in the position I want. To get it back to the original position, just reverse the process.

I hope this helps and is not redundant

[Michael Ray]

> To fix this problem- you rotate the fitting for the canister independent of the hose. To do this, grasp the canister while firmly holding the hose and then turn either the canister or the hose. It will put up some resistance but it will turn. I leave the canister attached so I can tell, where exactly I need to rotate the fitting on the hose, to get the canister in the position I want. To get it back to the original position, just reverse the process.

I hadn't tried to twist that hard but I'll give it a go. You don't keep twisting it back and forth do you? I figured having the connection midway between both positions (connection disc laying on edge) would suffice. My understanding is you always start upright and then flip the canister slowly to avoid any flaring so you're always using both positions.

[Tad Englund]

>You don't keep twisting it back and forth do you? I figured having the connection midway between both positions (connection disc laying on edge) would suffice. <
I just keep it in one position (inverted), because this is my winter stove and I use alcohol in the other seasons. You would only need to rotate it twice a year if it were your only stove. Once in the fall, then back in the spring.

>My understanding is you always start upright and then flip the canister slowly to avoid any flaring so you're always using both positions.<
I start with it inverted, you just need to be aware that the starting flame is different then in summer so "throttle down" accordingly. Practice this at home in the backyard before in your tent.

[Roger Caffin]

Hi Michael

> Do you reseal the fitting with something?
I did think about doing so, but decided to try retightening without at first. There seemed to be no problem, so I left it that. Yes, I DID check the fitting afterwards – submerse in water.

Some of the newer remotes (eg Primus) have a genuine rotating connection, so it is possible to rotate the canister freely. Very nice.

Cheers

[Roger Caffin]

Hi Michael and Tad

> >My understanding is you always start upright and then flip the canister slowly
> to avoid any flaring so you're always using both positions.
This is a safe method if the hose connection can rotate, but it is not essential. I sometimes start with the canister already inverted and the flame set very low. I give it about 30 sec before I turn the valve up any more – with the pot on the stove of course. The 30 sec burn heats up the preheat tube and gets rid of any remaining liquid gas near the jet.

If you turn the stove off with the canister inverted it is usually possible to turn it back on without any drama.

Cheers

[Brad Groves]

Hey, Lynn-

Have you used a WindPro in a Caldera Cone? Or a Ti-Tri? I'm thinking that the heat of the Windpro might melt the Cone, but not the Ti-Tri…? If you've successfully done it in the aluminum cone, that'd be great; my 2L one with a Windpro could be awesome for that 0*F weather…

[M G]

I've got a windpro and I've tried to rotate the fitting as described above. I managed to turn it so the canister could lie inverted without coiling the cable. When I tested for leaks before using the stove by immersing the connection under water there was a substantial amount of bubbles leaking. So I suspect I've done soething wrong. I tighened it back up rotating the conection back to its original posittion. Unfotunately it appears to still be leaking gaz at the connection, albeit quite a bit less.

I suspect I'm doing something wrong. Can you be more precise about what you are rotating, if you are using an adjustable wrench to do so, and pictures would be useful. I would love to get this stove to work in an inverted position without having the cable coiled up.

Thanks.

[Roger Caffin]

Hi Martin

The Windpro connection is actually a 'fixed' one. That is, there is no ability to freely rotate. Some stoves have some thread sealant on the connection at the valve/coupling which MOSTLY seals the thread even when the connection has not been done up tight. But this can let a few bubbles of gas leak out if the connection is not properly tight.

I suspect that many stoves have enough sealant there that the residual leakage does not prove to be a problem for the user. Some forms of the sealant stay a bit flexible and can handle some movement. Or maybe the users have not actually tested the connection under water. After all, a small bubble once every few seconds may not be found in the field as the gas would dissipate quickly and would not support a flame.

However, it may be that your stove does not have much sealant on the connection thread, and this is letting a very faint amount of gas leak out. I am going to have to put a public safety hat on here and caution against using the stove in this condition. It could clearly be dangerous.

What to do? You have three options:
* Do the connection up tight and leave it at that. Chancy.
* Get some liquid 'thread locker' and apply it before you do up the connection to whatever position you want.
* Try using a small bit of Teflon tape wrapped around the thread as a sealer.

Do test the result and do be a bit fussy: it's YOUR neck.

However …

The Windpro is quite old now. There are more modern equivalents – the very new Primus Express Spider has definite possibilities. The burner is out of the PackLite (I think), the legs are light and the coupling at the canister rotates by design. The weight is about 195 g. (Brass and steel – think about a light-weight version!)

Price unknown at this stage.

Cheers

[Tomas Reinhardt]

Edelrid Opilio 170g
Acecamp 4708 153g price: 30 Euro
Both with rotable coupling and better regulator for inverting canister

[Roger Caffin]

Hi Tomas

Interesting. URLs?
Bear in mind our readership is largely USA: we miss out on a lot of Euro stuff.

Cheers

[Franco Darioli]

Here
http://www.acecamp.de/en/Kitchen/
scroll down to art 4708, listed at 160g
Franco

[Roger Caffin]

Hi Franco

Hum, yes. Thanks.
I think I can identify the Chinese factory that came out of … :-)

Cheers

[Tomas Reinhardt]

Acecamp 4708 153g (weighted), my 113g mod: http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=23089

Edelrid Opilio 170g
Catalog Sports10-GB(8.28 MB) page 81:
http://www.edelrid.de/index.php?option=com_facileforms&Itemid=629
see also Stormy Evo with Heat Exchanger, Hexon multifuel 220g
Video(German):
http://www.odoo.tv/OutDoor-2009-Kueche-Special.548.0.html

[M G]

Hi Roger,

Thanks for the comments and the suggestion of the Spider, that and the other stoves posted by our European friends look lovely but unfortunately I am leaving in 4 days for a Sierra trip and need a cold weather stove now. This leaves me with a windpro and a bottle of loctite.

I completely unscrewed the connection and applied the loctite to the tube male part and rescrewed the adapter to the tube in the upside down position I needed. Once dry I tested it and it appears to be completely leak free…for now.

Thanks for the advice.

[Hikin’ Jim]

Tony Beasley wrote > …for winter my favorite is modified Coleman Extreme stove under a JetBoil GCS pot and I challenge any other stove pot system to melt snow as fast and efficient at 0F.

Now that is a fascinating idea. I'll have to try that. I assume you use a windscreen also? Any tricks to help avoid melting the neoprene?

HJ

[Roger Caffin]

Hi Jim

Tony will need to reply about using a windscreen, but I will bet you he did!

The neoprene – I worried that it would burn when I was testing several stoves with neoprene cozies. Somewhat to my surprise, I found that*provided the cozy was pushed right up to the rim* (so it didn't protrude at the bottom), there was no problem. The fins really suck the heat out of the flames. I found I could hold my hand in the exhaust stream beside the pot without any real problem. Try that with a bare pot! (DON'T!)

Cheers

[Tony Beasley]

Hi Jim,

I always take a windscreen with me, for the Xtreme I use and old and very crumpled, cut down MSR Whisperlite windscreen but last time I used my Xtreme/JB GCS pot in 0F conditions it was in a hut without a windscreen (pic below). The only damage that the neoprene cozy has suffered is from rodents eating it in the same hut, the little plastic covering on the feet of my Xtreme stove was also attacked and I lost my candle and my mate had his cup stolen.

Tony

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[Hikin’ Jim]

Roger, Tony,

Thanks, that's good information. The neoprene on JB's seemed at first to me to be a foolish thing (why put something that can melt on a pot for goodness sake?), but it's wisdom has become apparent over time.

HJ

[Roger Caffin]

Hi Jim

You didn't ask about wisdom.

My tests show the neoprene cosy has virtually no effect on the heating rate. But a lid has an enormous effect.

Cheers

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