cough cough!

[bob]

i have a small workshop and recently installed a pot bellied stove to consume all my scrap wood and keep me warm,i used a steel tube 115mm od as a flue with a rain cover on top,initially it went like a train and kicked tons of heat out but in the gales today i have had to evacuate sharpish as the place filled with chocking smoke,i have tried shielding the flue top but it made it worse,my question is i know i need something to combat the downdraught but all the spinners are very expensive and the non spinners look just like a rain stopper so have any other folks adapted or heard of someway to do it without a remortgage?,as always thanks for your help

[dom]

Must be a reason why you're getting a downdraught.

Does your chimney completely clear the highest point of the roof of the building, by a good bit - e.g 3 or 4 feet?

Is it long enough overall to generate suction through rising hot gases?

Are there walls/other-buildings/terrain nearby that the wind beats against - causing the air-pressure to rise near your chimney outlet?

Are there lots of airleaks in the building, causing it to depressurise towards the side in the shade of the wind?

[Matty F]

I made a chimney cap like a flying saucer with a gap around the edge and that seemed to work. I made it out of two old aluminium oven trays. Imagine two saucers facing each other with a gap between them. It's also necessary to have a window or vent open on the side of the worshop where the wind is coming from.

[Andy Dingley]

Get the outlet high up and clear of other obstacles.

Then if that doesn't fix it (and it's a small woodstove, not a coal fireplace) then try a H pipe.

[Jules Richardson]

Are ones for chimney use significantly different to those used for ventilation? Reason I ask is that my local building reclaimation place sells used ones for what amounts to a couple of beers - but I just don't know if you can stick them on chimneys, or if they're likely to jam solid sharpish...

[cynic]

There are "H" terminals and there are "OH" terminals. When I worked for the Shell heating agency for my area it was stated by Shells technical lab that the OH was the only one which actually worked consistently for naturally flued boilers

[Dave Liquorice]

Reverse your thinking, it might not be the wind blowing down the flue but the air being sucked out of the building and thus pulling the smoke back down.

I suspect most of the air entry into the building is on one side and that side is in the lee of the building and thus a low pressure area compared to the exposed side and chimney top. Close/block holes on the lee side and open on the exposed.

Air flow through buildings is not as simple as it might first appear. Remember air only moves due to pressure differentials.