What is the best type of fluepipe cap for windy conditions?

[adama]

I’m having starting problems with a 150mm sidewinder batchrocket mass heater. When the heater is cold and there is any significant wind there’s a lot of smoke blowback when trying to light the fire. The system doesn’t have a bypass because I assumed that the flue height of around 9 metres would create sufficient draw - even when cold. The bottom 2.5m of pipe are single-wall, the rest is insulated double-wall.

The current fluepipe installation has the top of the pipe about half a metre above the high side of the single-pitch roof, however there is a large brick rectangular chimney structure nearby that is slightly higher than the fluepipe and I expect Is causing turbulence that leads to the blowback. I’ve advised that another metre length of pipe should be added to put the terminal in “cleaner” air.

As an additional improvement I’d like to change the cap on the pipe. The options available are:
1. a simple conical cap
2. a conical cap with a band around it (this is the current cap)
3. a “girandola” that spins round when the wind blows
4. a “Saturn” cap - which looks like a stack of 4 or 5 rings with a conical cap on top
5. an “H” shape

If any forum members have tried different caps I’d be very happy to hear your experience.

Many thanks.

[peterberg]

Your chimney height and insulation is really good, one meter more won't make it better. In my case, there's an appartment block just 10 meters away and I had quite some problems during the first winter even with a special "saturn" type cap. The block is about 9 meters higher than the chimney's exit, length of chimney approximately 6.5 meters in total.

Seven years ago I switched to a girandola cap (nice sounding name by the way) and all problems were gone. My girandola is made by Darco in Poland, I bought it in the Netherlands. It fits inside the chimney pipe, the top half can be tilt away and the cap's bearing is mounted outside the cap itself.
Here's a picture:

[Vortex]

I used one of these last winter, it's ugly but very effective: www.windkatcowls.co.uk/