Cowls: Bird, Rain, Draught

Cowls, overview:

Most chimneys work well, so there is no need for special pots or cowls to improve chimney performance.  However, a cowl or similar to prevent unwanted ingression from birds, vermin, or rain may be well wanted.  Conversely, if there is a downdraught problem, then an anti-downdraught device should/must be considered.



Chimney cowls regularly get clogged with flue deposits, it is vital these are removed so the chimney can work properly. Generally, it is sufficient to bonk the cowl with a sweeping brush or the brush-guide-ball, which will normally clear sooty ones. For cowls laden with tar or encrusted creosote, the use of flue cleaning powders or logs prior to sweeping will be very helpful. Fumes from these chemicals render the tarry substances ‘brittle’ with less adhesion, so as the mechanical actions of ‘brushing & bonking’ will more readily remove them. However, to get the cowl cleaned properly, a roof climb is sometimes unavoidable. Subsequently, three key factors regarding cowl design need to be considered.

(1) Fixing – The cowl has to be secured to the chimney or pot so as it does not become detached, i.e. ‘wire balloons’ and ‘witches hat’ cowls, by design are poor. Also, the hook-type cowl anchorage is often poor. The best fixing system is a quality ‘fully-perforated’ stainless steel ‘worm-drive’ band that grips the cowl’s vertical holding straps onto a suitable pot. Be mindful when tightening, that via the various ‘thermal expansion & contraction’ rates of terminal materials, stress and damage can be caused. Also, if the pot is tapered the band could, over time, work loose.

(2) Strength – The integral strength of the cowl needs to be such that it can withstand the bonking forces, accidental or deliberate. Notably, the weakest part of ’wire-sided’ cowls, is the lid-to-strap joint. Here the screws, rivets, or welds, often rot due to exposure to weather, and caustic chimney chemicals - burning sulphurous coals will greatly exacerbate this.

(3) Corrosion – Chimneys, their pots and cowls, all suffer from very severe chemical, heat, and environmental attack. Thus for longevity, the best materials to use for making chimney cowls and pot terminals is either a suitable stainless steel, or an appropriate clay.


Bird, Vermin, & Rain cowls:

Intrusion from birds and vermin causes distress to human occupants of the building - and ultimately, it is often fatal for intruders…  Clearly, nests within chimney flues will render them useless, and introduce a fire hazard. Rain ingression is not normally serious in open fireplaces.  However, water will mobilise caustic chemicals contained within the chimney, exacerbating attack on mortar and other chimney lining materials. Similarly, when a stove is fitted, any water entering it from the flue may be caustic – and this will attack the flue collar, baffle plate, and other metal parts within… Thus a dry chimney is always better for several reasons.


Wire sided cowl problems:

(1) Rain – They will let in rain during stormy conditions

(2) Clogging – Exhausted ‘soot, creosote, or tar’ can adhere to cowl wires, and fill the gaps on the leeward side. This can in time, cup and channel wind down the flue, and thus actually cause a downdraught!

(3) Corrosion – Poor quality ones, made from corrodible materials will quickly rot and not last long. For durability they need to be strong, especially at their lid-to-strap joints. The best are and made from stainless steel.



There is a plethora of pots and cowls to choose from.  Changing pots can be an expensive exercise, sometimes complicated by architectural style issues and availability. Standard cowls are not very expensive, and most can be fitted from ladders by good sweeps, stove installers, or competent DIY people. Preventing nesting and rain from entering the chimney flue is always worthwhile.

If the chimney is to be made redundant, be mindful that sealing it off will stop natural flue ventilation, which may be a required factor. Should a suitable termination device, like a ‘pepper-pot pot insert’ or ‘bonnet-insert’ be chosen, the chimney must not be used.


Some conventional cowls & cap:


Anti-downdraught cowls, overview:

There are various reasons for downdraughts; a detailed discussion can be found on my Technical Points page.

There is a host of devices designed to tackle downdraught problems.  The range of capabilities of each, together with all respective costs, should be considered comprehensively during your selection of the ‘good, bad, & ugly’!

Some cowls work for a limited time, some don’t work at all, some are difficult to sweep, and others just look so ugly - do you want them on your skyline? Beware too of those that cannot be supported by the physical facts within their design solution – or you could end up like the naked Emperor!


Some anti-downdraught terminal devices:


Skyline solution:

Skyline Smart Cowl (all-in-one)..!

Having given the matter thought, I designed the Skyline-Smart-Cowl.  It is now made to high standards on state-of-the-art precision CNC machinery in the West Midlands (England), from high quality materials.

When choosing your cowl, we suggest all the features and properties as required are given balanced consideration. Also, please do not underestimate the importance of future sweeping, and the facilitation to do this easily…


* Easy to Fit – all fixings included
* Suspends Flexible Flue Liners
* Excludes Birds & Vermin
* Protects Register Plate
* Suitable for all Fuels
* Cures Downdraughts
* Eliminates Rain
* Rustproof
It’s better by design…
 Skyline Cowl - Metal

Skyline Cowl - Masonry






All of the many Skyline cowls now fitted,
are working superbly well…


For: Wood, Oil, Gas
Size Material Price
6″ Aluminium £120
8″ Aluminium £160
For: All fuels, including Coal  
Size Material Price
6″ Stainless Steel £140
8″ Stainless Steel £180
(1)   Use 8″ cowls for fitting to pots or onto stack crowns
(2)   Use 6″ cowls to suspend flue liners, in general
(3)   Payment is required prior to dispatch

…Contact us soon for yours!



Cowl comparison chart:

Feature requirement  -by-  Cowl type

  Wind Rain Bird Sweep Life Fix  Look Oil  Gas  Wood Coal  Cost %    
Balloon 0 0 10 3 5 0 8 0 10 0 0 10 38.3
Witch 0 0 10 3 10 0 6 5 10 8 6 8 55.0
‘H’ Type 10 10 10 0 6 8 0 6 10 6 3 3 60.0
Spinning 8 8 10 5 3 5 3 5 10 8 6 3 61.7
Vane  8 8 8 6 6 8 3 6 10 8 7 0 65.0
Cap 0 7 0 10 8 10 8 5 10 10 10 8 71.7
Cage 3 5 10 10 8 10 3 8 10 10 8 6 75.8
Vadette 10 10 10 5 10 10 8 10 10 4 2 5 78.3
* Skyline 10 10 10 10 10 10 10 10 10 10 10 5 95.8

 * Skyline – made from stainless steel


Customer’s review (verbatim):

“Tim fitted a Skyline pot (is that what it’s called?!) onto our chimney after years and years of fire trouble in the house. The previous owners had resorted to a very expensive electric fan as the only solution. After a very reputable stove shop diagnosed the problem, they recommended Tim and his Skyline pot above their own products. (Remove that if it will get anybody in trouble!). Tim assessed the issue and was kind enough to fit the job in before Christmas. The service and price were superb, Tim even cleaned the stove for us and took the time to explain how our log burner worked. The Skyline pot has TOTALLY fixed the problem, some very high winds have put it to the test! We are amazed that after almost a decade of electric fans and smoke-filled rooms the chimney is finally working as it should. We can’t thank you enough!”
Alice, Sheet Rd, Ludlow – December 2015




We’re sweeping the Midlands & Marches…

07580 958346

…Why not brush-up, with us?





Please Note:

All novel aspects of ’Skyline’ cowls are the legally protected intellectual property of Skyline Activities Ltd


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