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Hi all,
I've moved into a house with a morso stove with rear-flue exit that has real problems in southerly winds - ie a lot of the time. Is it wishful thinking to believe I might sort out some of the draw issues just by moving the stove back in the hearth so that the flue runs straight up from the top?

[Logic, which might well be flawed, is that flue gasses would have less distance before the vertical bit of flue, and fewer wiggles]

Thanks

CharlieB wrote: ↑Wed Nov 09, 2022 6:25 pm Hi all,
I've moved into a house with a morso stove with rear-flue exit that has real problems in southerly winds - ie a lot of the time. Is it wishful thinking to believe I might sort out some of the draw issues just by moving the stove back in the hearth so that the flue runs straight up from the top?

[Logic, which might well be flawed, is that flue gasses would have less distance before the vertical bit of flue, and fewer wiggles]

Thanks

My gut feeling is that it's almost always the top of the flue that's the problem, rather than the bottom. I had similar problems many years ago, with a different make of stove, and these only went away when I had the chimney filled with some sort of lightweight insulating cement. It had been a big square flue (it was an old granite cottage) and I had a company come around and drop an inflatable rubber liner down it, seal this at the bottom, then inflate it and pump in the lightweight cement stuff from the top. At the same time they fitted a proper terminal to the top and after this was done all the problems we'd been having went away.

Not sure if it was the better insulation of the flue lining material, keeping the gases warmer as they went upwards, the reduced size of the flue increasing the gas velocity or the new terminal on the top, but it transformed the performance of the stove. It also stopped the problem we'd been having with smelly creosote dripping down the chimney and pooling in the bend where the rear flue exit turned around to connect to the chimney.

You’re right, logic (man logic ?) says a straighter flue path is going to help. It may.

Before you start drastically changing things, consider if there are any competing air flows that may inhibit the flow in the flue.

Presume the flue is lined ?

We have a stove with the flue on the south side of the house - with strong prevailing (usually SW) winds, we have to really throttle back the draw - ours is a rear exit flue.

I’d take a very cautious and sequential approach to fault finding.

I was forced to change ours from top to rear to join the glazed chimney terracotta flue to exit the room space, wierd as it then is regular brick up top, half n half.

On the fens, north & south winds prevail, a "hill" woodland all cause problems, but only a handfull of days per season.

Decent terracotta H pot will / should be first consideration imho.

neighbour had one, no problems, & they ran an open fire
WBS roars due to firebox room & chimney, ala blast furnace.

Would invest in the H as likely that will sort it, pricier but...

I'd go hunting on the net for that specific stove type snd see if there are any idiosyncrasies? I have both a top and rear exiting stove. Different makes and completely different behaviours. Pros & cons for both.

Go back to basics and ensure you build a thin kindling pile that will take off like a rocket. I build base log, kindling pile and top log about 1/3rd the size of the base log. Never fails. My super secret assistant is a toiletroll tube. Concentrates and funnels that flame to a ridiculous degree.

CharlieB wrote: ↑Wed Nov 09, 2022 6:25 pm Hi all,
I've moved into a house with a morso stove with rear-flue exit that has real problems in southerly winds - ie a lot of the time. Is it wishful thinking to believe I might sort out some of the draw issues just by moving the stove back in the hearth so that the flue runs straight up from the top?

[Logic, which might well be flawed, is that flue gasses would have less distance before the vertical bit of flue, and fewer wiggles]

Thanks

I have a Morso stove and using the rear flue exit as well and generally have no problems with the draw. Very occasionally I find that on opening the stove door I can feel cold air coming back down the flue, this seems to have no bearing on outside temperature or due to high winds. So before lighting the fire I use a hot air gun to blow hot air into the stove and as soon as I feel the flue getting slightly warm, I can light the fire, if I don't do this the fire normally just goes out after lighting it. Our flue uses a stainless flexi liner that is also insulated and in the 20 years the stove has been in use there has been no creosote in the liner, and it has never been swept (only a small amount of light brown ash seen at bottom of flue.
The flue has one of these on the top:-

Didn't have any problems with downdraft during any of last year's storms.
Might be worth saying what kind of flue you have, the length of the flue and any other pertinent details.

Is the problem at lighting or once up to temperature?

Once the flue is at temperature it should just be sucking the exhaust gases up and short of some very weird fluid dynamics at the turn from the horizontal into vertical part of the flue and the real problem would be a back draft which would exist at the chimney pot.

So many variables.

Jenga tower FINE slivers of kindling, not blocks, warm the chimney = increasing the draw.
Got a weather pressure monitor for more insight as to variables?

If it's just at lighting, in very strong winds, try opening a window/door on the side of the house facing the wind. To try to get a better pressure differential between in the room and at the roof. I made the mistake of opening a window on the side of the building in the lee of the wind after some downdraft issues - BIG mistake, room filled with smoke. Made me think to try it the other way around.

You can get a plug of cold air stcuk in the flue, so heating the flue an help with the lighting process.