Fire going out dependent on weather, room pressure?

[neiln]

7 hours ago, Pacemaker1000 said:

It’s on an extension roof over 10’ away from main building and 2’ above that

You probably meet regs for the flue height due to distance from the main roof BUT what you've got is a fairly common problem.  It's where the main house, through it's height, has a comparable chimney effect or draw as the flue.  Ie, the house is trying to act as a chimney and as it's higher than the flue it's nearly a better draw.  If you close doors between the extension and the main house and close all upstairs windows and doors you'll probably see the house less effective as a chimney and the stove work a bit better, that's proof.

The solution is a taller flue.

[Pacemaker1000]

1 hour ago, JLA1990 said:

Had a stove company round yesterday  coincidentally taking a look as I’d like a stove in the extension. The stove will be over 2.3m from the old external wall, and the surveyor said the flue would need to be a minimum of 4.5m from the top of the stove. He then suggested it may need to be higher to improve the draw on the fire but the 4.5m is the minim reg requirement. 

thanks, I’m thinking it’s worth trying removing what looks like a 50cm section and  replacing it with a 1m one and maybe a anti backdraft cowl

[openspaceman]

41 minutes ago, neiln said:

You probably meet regs for the flue height due to distance from the main roof BUT what you've got is a fairly common problem.  It's where the main house, through it's height, has a comparable chimney effect or draw as the flue.  Ie, the house is trying to act as a chimney and as it's higher than the flue it's nearly a better draw.  If you close doors between the extension and the main house and close all upstairs windows and doors you'll probably see the house less effective as a chimney and the stove work a bit better, that's proof.

The solution is a taller flue.

Yup I have seen this very scenario when a wood burning range was fitted in a single storey kitchen of a 2 storey plus dormer centrally heated house.

[Stubby]

9 hours ago, Pacemaker1000 said:

thanks, I’m thinking it’s worth trying removing what looks like a 50cm section and  replacing it with a 1m one and maybe a anti backdraft cowl

That stack needs to be higher than the ridge of the main building . Because its not is the reason that when the wind is in a certain direction it affects the draw . If its above the ridge this won't happen .

[Steven P]

2 hours ago, Stubby said:

That stack needs to be higher than the ridge of the main building . Because its not is the reason that when the wind is in a certain direction it affects the draw . If its above the ridge this won't happen .

 

 

I've done some internet reading - and I'd agree, the solution to the problem is a taller chimney, how big I am not sure.

 

Cause of the problem could be a combination of turbulence off the roof ridge creating a higher pressure in the chimney - forcing the smoke to go down, and a taller well sealed building next to it creating a chimney effect. Chimney effect - when the wind blows past a ventilation brick in the house, an upstairs open window or roof tile vent (I think well sealed houses need some sort of vent bricks in to stop them getting damp?) physics says the wind will suck air out the house, plus some 'heat rises' from central heating. A combination of the 2, wind blows over vent, lowers upstairs internal pressure, and then causes turbulence on the other side above the chimney.. and smoke goes downwards. On their own both features are OK, in this case together a problem is created.

 

Taller chimney and turbulence effect is reduced and taller chimneys draw better (so long as not stupidly tall that the flue gasses get cold as they rise)

[Stubby]

15 minutes ago, Steven P said:

 

 

I've done some internet reading - and I'd agree, the solution to the problem is a taller chimney, how big I am not sure.

 

 

Just taller than the ridge . ( as in an original  brick built chimney on a standard house )  As you say heat the flue first with the door open just a crack for 10 mins then adjust the stove to suit .

[Pacemaker1000]

A taller flue is definitely worth trying. Neighbour has almost identical layout, only difference is their extension has a flat roof. So although total flue height is the same it has a lot more room beneath and around it.

[neiln]

I can't see how that would make any difference.

 

Beside a taller flue, sealing the stove from the room and thus the house's stack effect is an option and possibly why you've got the outside air supply.  You'll have to open the door to load logs and risk a little smoke spilling but the flue being hot should power the draw and overcome the house enough. So I suggest you look into whether your outside air is effective, the stove is properly sealed from the room, and I'd still look into raising the height of the flue.

[Pacemaker1000]

Luckily got a guy in the area and came around straight away.

recommended extending external flue by 1m and removing the two internal elbows.

ordered and should be fitted tomorrow so fingers crossed 🤞 

[Stubby]

2 hours ago, Pacemaker1000 said:

Luckily got a guy in the area and came around straight away.

recommended extending external flue by 1m and removing the two internal elbows.

ordered and should be fitted tomorrow so fingers crossed 🤞 

He recommended extending the flu ? really .....

Edited November 30, 2022 by Stubby