DIY stove jack- Glue-on and sew-on for hot tents

This post is about the use of RTV silicone rubber and cotton to create a DIY stove jack. It protects a tent canopy from the heat of the stove pipe when used in an ultralight tent while hot tenting. They are designed to be glued and/or sewn to the tent canopy.

It is for ultralight camping and adventure gear. It is a work in progress and reports favourably on a composite of RTV silicone rubber and shirt cotton fabric to form a simple, compact, universal, and soft stove DIY ultralight stove jack.

Introduction to DIY stove jack

The combination of ultralight tents and tent stoves raises challenges with regard to protecting ultralight tent fabric from heat damage from a hot flue pipe where it passes through the fabric of the tent canopy. A DIY stove jack can provide heat protection while keeping the tent canopy soft and stuff packable.

Beware of run-away burns

While mildly heat-tolerant solutions may suffice for most circumstances, a considerable safety margin should be allowed for the unusually hot combustion that may occur infrequently with ‘found’ bush fuels.

The rare runaway flue pipe burn in the photo below is such an example. It was not even noticed at the time but was accidentally recorded during automated time-lapse photography.

Traditional stove jacks

For tent stoves, fibreglass and silicone flat stove jacks or molded silicone stove jacks have become the standard. However, I have rejected these protective measures because of the weight, bulk and stiffness that interfere with the efficient stuff packing of my ultralight tent canopies. As an alternative, I have successfully used a glued-on pocket that holds a thin flat aluminium foil heat protector/dissipator or what I called a tent flue gland.

Knowing stove pipe temperatures

The safe design of a DIY ultralight stove jack depends on knowledge of the burn characteristics of the particular stove and the maximum sustained stove pipe temperature that will be reached at the intersection of the pipe with the tent canopy.

I will use my KISS Stove as the model to determine stove pipe temperatures. This stove has a steady and miserly fuel consumption rate (~7g/minute) and high heat exchange efficiency.

Consequently, it has a stable and relatively low stove pipe temperature. The temperature on the pipes of most other stoves that are batch loaded may be considerably higher and potentially much more variable.

Also, I will focus my measurement high up on the stove pipe where it passes through my pyramid tents near the apex. I discuss tent stove location optimization in pyramid tents in a separate post. I discuss stove mounting methods in another post; tent stove mounting for all seasons. My favourite is elevated mounting on bush poles that are driven into deep snow (or soil), will also influence the pipe/canopy intersection point.

Understanding the variability of the relevant stove pipe temperature is a good start for designing the stove jack. Design for the maximum and for some more.

Mothy The Elder

Stove pipe temperatures, first quality measurements

Thermocouple

For the first time, I had a sweet and cheap thermocouple and meter package that could estimate high (1,300C) stove temperatures with some accuracy as reported in; a cheap thermocouple for effective stove tinkering. It would be a big improvement on my infrared thermometers that were easy to use but limited to 550C. I knew that they could seriously underestimate and overestimate the temperature of stove surfaces.

The thermocouple meter responded quickly to changes in temperature and stabilized quickly when contacting a surface with a steady temperature.

A thermocouple holding rig 1

To hold the tip of the thermocouple steady against the hot stove pipe and insulate it from heat loss I made a welded tight-fitting fine stainless steel band (20mm long) out of 0.1mm thick foil (as shown below). On the side of the band, I formed a welded ‘D-shaped groove into which the thermocouple could be squeezed tightly.

Temperatures at the base of the stove pipe

I started my measurement down low on the hottest part of the flue system to do my first test. I ‘cranked-up’ the stove, using fuel of thin fast-burning little sticks, (As shown in the photo above.). I recorded temperatures between 250-300C.

Temperatures of the stove pipe at the intersection with the tent fabric

Next, I set the thermocouple at a height of about 1,800mm above the stovetop as this was near to where the flue pipe would exit the canopy on my pyramid tents. It was also at a height where, when camping, I routinely stand up to do periodic ‘spit tests’ to monitor for an ongoing very safe exit contact temperature of about 100C.

This crude field test ensured that there is a very big safety margin. The 100C spit test also is a simple indicator of good stove draft, clean combustion, and heating performance.

Also with this temperature, there will be no build-up of creosote, tar or significant soot in the roll up stove pipe when it comes time to pack up. It also ensures that the water in the fuel exits the stove pipe as steam in winter when the fuel sticks are invariably damp.

At this height of 1,800mm above the stovetop, I measured 103, 104, 110, 111, 114C and an aberrant 143C. I was delighted that these measured temperatures concurred with my crude ‘100C spit test’ that I have trusted for many years. Importantly even the aberrant temperature measurement was not above the maximum safe protracted working temperature for silicone rubber of 150-200C according to Shin-Etsu silicone. It this is confirmed and additional could periodically stray up to 300C without significant harm according to Jebco.

Temperatures along the stove pipe

For those stovies who may not make their stove pipe exit near the apex of the tent, I measured the temperature along the stove pipe with the KISS stove running flat out (That’s its only setting!). The temperature at the bottom of the stove pipe was 300C. At about 400mm from the stovetop it was 266C, at 600mm 150C at 1300mm and 143C at 1800mm.

Alternative DIY silicone rubber stove jacks

A pure silicone rubber stove jack

A thin silicone rubber gasket sheet with a suitable hole for the flue pipe cut in it could be used as a stove jack if it could be reliably glued, with RTV silicone rubber, to the tent fabric.

However, in another post on such glueing I show that not all fabric, even silnylons make a strong enough bond to survive the rigours of camping without supplementary stitching. Also, this stiff and thickish gasket rubber will create an increased tendency to peel off during stuff packing when the glue bonding is not optimal.

A softer, thinner, and more compliant sheet might hold better in this situation, but it would not be so suitable for robust stitching and would not provide good lateral support for the stove pipe in storms.

Consequently, a universal DIY stove jack would benefit by having a fibrous perimeter that could be both glued and sewn to the tent.

A fibrous cotton silicone rubber composite

I have shown that DIY RTV silicone rubber impregnation and embedding are easy and practical with simple cotton shirt cloth and other fabrics. I expect that they could provide a suitable high-temperature resistant boundary zone to attach onto tents where the hot flue pipe passes through the tent canopy. It would be very suitable for both glueing and sewing to any tent fabric. In a separate post, I show that silicone rubber-impregnated cotton can withstand contact with a 290C metal surface.

A shirt cotton/silicone rubber DIY stove jack

A simple stove jack could be made of the above fabric. It could just be a rectangle of the fabric with a suitable hole for the stove pipe cut in it. However, the thin edge of the hole may not provide adequate lateral support for the stove pipe in storms. Also, at higher contact temperatures the embedded cotton may start to charr.

A high-temperature stove jack with a soft cotton/silicone glueable and sewable tent interface

For very little extra effort, an extra high-temperature boundary layer could be added to the cotton/silicone. This could be:

• Pure silicone rubber sheet,
• In situ molded RTV rubber, or
• Fine metal foil such a stainless steel or aluminium for the most extreme temperatures.

The successful bonding of the above materials and many more using RTV silicone rubber has been described in another related post on RTV silicone rubber uses for backpacking gear.

DIY silicone rubber composite stove jacks that are both glueable and sewable

The following series of photos show the various ways of making glueable and sewable soft stove jacks. I have delayed the metal foil variant in the hope of doing something more innovative.

A DIY stove jack from silicone/cotton and silicone sheet

A DIY stove jack from silicone/cotton with an extra boundary layer of bonded RTV silicone rubber

This stove jack has a final boundary zone that is about 10mm wide where it meets the flue pipe. This zone is made of pure RTV silicone rubber as an extension of the flexible cotton/silicone jack. It transitions to a 10mm wide ring of silicone rubber only.

The ring is somewhat thicker than the embedded cotton so that it has considerable strength to hold the flue pipe firmly in place during windstorms. However, the silicone rubber ring is soft enough to stuff-pack easily while backpacking.

The stove jack can be glued to the tent canopy if the fabric of the canopy is suited to strong bonding. If the bonding has deficient peel strength, as described in RTV silicone rubber uses the glueing can provide waterproofing and supplementary stitching can prevent peeling (shown later).

Stove jack with a heat-resistant weather flap

For comfort and convenience, a stove jack should have a cover that is easy to use and will never be ‘left at home’. It should be very light and suitably heat resistant to be able to simply rest against the hot flue pipe while the tent stove is in use. While lifted in its lifted state it also can act as an effective snowmelt/rainwater flashing gutter over the hole in the tent.

When I tested the stove jack, the flue pipe, at the contact point, reached a maximum of ~170, so degradation of the cotton/silicone was not an issue

However, other conventional batch-loaded tent stoves may have much hotter stove pipe temperatures and the rules may be different for them.

I found that the flap stuck to the hot flue pipe a little. There was a tendency for the flap to get pulled (or pumped) down into the hole with the action of stormy wind gusts on the tent.

I deployed the foil cover that I made in case it was needed as a heat shield for the flap, but it was not needed for this purpose. However, I noticed that it stopped the sticking of the flap to the flue pipe. A simpler option will be added to the post sometime.

A prototype removable metal heat shield is shown below with an additional loop of cotton glued onto the flap to allow a bush stick to be arranged to prevent the foil from slipping off. I made the shield have a large area so that it would be able to easily dissipate any heat that would transfer to it from the flue pipe.

The fitted DIY stove jack

To put the above stove jack into action, I removed a pocket and metal foil style stove jack from one of my DIY pyramid tents. Then I glued on the new cotton/silicone stove jack. The tent was made of a type of silnylon that formed sub-optimal bonds with RTV silicone rubber (as described above). Consequently, as a precaution, I hand-sewed on the new stove jack to supplement the poorer peel strength of the bond.

However, I was delighted by the considerable force that was required to peel the original pocket off. “No windstorm could have knocked it off. The residual silicone glue took some time to remove from the tent in preparation for glueing on the new stove jack. It still looks a bit ugly as the glued area of the old pocket was much bigger than that of the new jack and small bits of silicone can be seen. I doubt that this blemish will offend the snow gods and they will continue to occasionally send us delightful fluffy snow to ski in.”

DIY stove jack attachment practicalities

Tent with an existing stove pipe hole. Fitting the DIY stove jack to a tent that had a previous stove jack hole cut in it was a bit fiddly. The small wrinkles, as can be seen in the above photo, were unavoidable because of the instability of the fabric around the cut hole.

Tent without a previously cut stove pipe hole. When applying the jack to a new tent the process is much easier. An elliptical disk of thickish polythene sheet could be used to mask out the glue at the outer edge of the silicone ring. It can be temporarily stuck in place on the tent surface with a little bit of RTV silicone rubber. “It will easily peel off the polythene when cured.” This would make it easy to cut the hole in the tent fabric at this glue line after the glue cures. It will easily allow a suitable but minimal clearance to be set for the hole from the adjacent tent seams.

The sewing through the cotton/silicone was quite surprisingly easy, either by machine or hand stitching. The photo show hand stitching and I chose this because in the back of my mind I thought I may, one day, wish to replace it with an even better* stove jack. Hand stitching will be much easier to undo. There was another secret reason for this decision, but that will have to wait for another post.

Note about my stove jack evolution*. My latest universal soft silcotton stove jacks can be formed as part of the tent panel before tent seam stitching is done. This means that the connection of the jack to any tent fabric is simple and not dependent on glueing and it also allows the jack to be more compact and be located closer to the tent apex which is very stable during storms. This new jack includes a glued weather flap and can also have additional flaps to accommodate multiple stove pipe diameters. For more details please see my post; DIY universal stove jack.

An extra thermal protection sleeve for the hole in the DIY stove jack

If for larger bach-fed stoves the flue pipe is hot enough for the above flap to require protection with metal foil, then it follows that the hole in the silicone rubber jack would also need similar protection. This could be as simple as a guard-tube made from a wrap of aluminium foil. The foil that can be cut from a small soft drink could be very suitable.

The sleeve can be made open so that it can be easily opened up to wrap around the flue pipe and passed downwards into the stove jack from the outside of the tent.

Alternatively, in bad weather, I fitted the jack from the inside of the tent and the flue pipe can be smoothly passed up through it. The tag on the bottom of the sleeve can be used to tie it down during wind storms and the hinged red silicone rubber flap can be used to stop the sleeve from falling down

The original curvature of the drink-can makes the aluminium foil ‘spring’ outwards to fill the stove jack aperture. This means that there is an air insulation space between the flue pipe and the sleeve and there will be limited capacity for heat to conductively transfer to the protective sleeve. The large area of the aluminium foil and the draft formed in the space will help to dissipate the heat that is radiated into it.

To test if the heat shield worked, l run the KISS stove flat-out. “Well, that’s its only setting as it is designed to run flat-out without any air restrictors or dampers!” I measured a maximum 170C on the flue pipe just below the guard tube, and at the same time, 100C on the outside of the guard tube. This 70C reduction of the contact temperature with the rim of the stove jack seemed like a good achievement.

The guard tube is very light (~5g), cost nothing and can also be rolled up for efficient and safe backpacking within or around the KISS stove roll up flue pipe. It would make a prudent addition to your kit, especially if you don’t accurately know the maximum stove pipe temperature.

Conclusion

A composite-cotton and RTV silicone rubber DIY stove jack can provide a light, cheap, compact, soft, simple, elegant and backpack-worthy heat protector for an ultralight tent stove such as the KISS Stove. It should be able to withstand flue pipe contact temperatures of 200C.

An extra guard tube could be used to raise the safe temperature to 300-400C for larger and less efficient stoves. Such a guard tube could be made with aluminium foil from a soft drink can.

Addendum 1

I was fitting a stove jack to a new experimental pyramid tent that is made out of polyester umbrella fabric. I found that the silicone glueing was rather inadequate. I thought that the silicone cotton stove jack could be simply sewn in, as a substitute for a small part of the tent fabric. “It would have been much easier to do it upfront before sewing the tent panels together, but that is the wisdom of hindsight”.

Anyway, I decided to cut away a small part of a tent panel near the apex. I left the lay-flat seams intact on each side to maintain the strength and rolled some of the panel over to sew it onto the seam to enclose the raw cut edges. The custom-shaped stove jack was fitted with glueing and sewing to the remnants of the tapering tent seams.

Addendum 2

Directly sewn stove jack. In my latest larger pyramid tent with a vestibule, I added the stove jack to the top of a tent panel before sewing the panel into the new tent. This made the process very neat, easy and strong. It means that the jack can be securely attached to any tent fabric (including my polyester) by stitching with or without glueing. For more details please see my post on a Pyramid tent with a vestibule.

Universal stove jack for various pipe sizes. The Universal DIY stove jack that I put in the above vestibule tent has been made so that the jack can be used with multiple stove pipe sizes. The smallest one is for my tiny KISS tent stove and the largest one is for my Large downdraft tent stove.

Tim