We get backwinding especially with gusty SW winds which have been prevalent recently. The house is behind and to the side of the main block of houses which are to the South.
I'm looking at:
How do these work? Does anything move? Or are they just about producing some venturi effect at the chimney exit?
We don't have an airbrick into the lounge (where the fire is). What sort of size is needed to allow sufficient air to fuel the fire?
a hole big enough to get two fists through
The problem is likely caused by vortexes generated by the nearby building on windy days. There are various rules concerning chimney heights to get above the vortex .
You will see devices to help which may or may not be efffective, you can never be sure. They will make the chimney more likley to tar /soot up and harder to clean.
Many houses are draughty and rely on this for ventilation. Lack of ventilation can cause problems if you are well draught proofed. To check ify ou have a problem, just open a window.
You can see what's happeningby dropping small pieces of paper in front of the fireplace and seeing if they get sucked into the fire/up the chimney.
In the end, you may need a higher chimney.
Probably a stainless steel one would be cheapest and best.
Masonry chimneys take a while to warm up (hours in some cases) and function correctly, this may be (part of) the problem. This can be got round by a chimney lining.
I asked our chimney sweep about the problem we had with our fireplace in the living room when we had Southerly winds, and he recommended on of these (a "Colt Cowl");
It worked a treat and we've never had problems since.
I was looking at a group of houses somewhere recently, and they all had revolving cowls.
is this an "old" house that would have had single glazed timber frame windows and ordinary timber doors with little draught proofing? Has it now got double glazing and sealed doors?
Air flow round/though houses is very complex, different combinations of doors open/closed, even quite a distance from our old open fire could make it smoke out of the under grate vent (It was a Baxi Burnall) or draw air in that way. It never smoked out of the actaul chimeny though. One very still and cold nights air would come down as you could smell it.
Next time it happens open the window in the room a bit and see if it cures the problem. If it does fit an air vent, two air bricks ought to be enough for a normal open fire, stoves above 5kW (IIRC) start to have the size of the hole specified in so many mm^2 of "free air". What is deemed "free air" is laid down in the Building regs.
It has always (in my 30yrs occupancy) backwinded with gusty winds from the S & SW even before double glazing. No amount of opening/closing doors/windows helps other than to clear the room of smoke.
Today is fine - NE wind. My hunch is that a "vacuum" is created in the passageway between my house and the upwind house.
The only saving grace has been that generally it is not so cold when the wind is coming from that direction, and the fire draws well when the wind is coming from the traditionally cold directions in the northern quadrant, and in fact I wouldn't generally want it to draw any better.
That one looks to be just static aerodynamics. There are other types that do have moving parts:
For extreme cases, there are even ones with electric fans.
I may have a problem then of overdrawing when the wind is coming from a 'good' direction. Ideally I want something that will react only when the wind is from the S-SW.
And add a sensor switch so it comes on when the wind is from SW, or switches off when it isn't!
That's brilliant - thank you.
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