Charnwood Downdraft fix with external air vent.

[Gtflash]

Evening all.  
 

had a Charnwood Arc 5 on twin wall external 6” since July 5kw unit.  We love it can’t seem to go a night without it.  
 

Unfortunately it can be tricky to light, sometimes.  Whilst building the fire you can feel the downdraft and it’s enough to blow out a candle or fire lighters or newspaper and force all the smoke out the bottom vents.  CO alarm went off at 3am about three weeks ago so Last week we had an anti downdraft cowl fitted which has made no difference what so ever but luckily no CO alarm.   We have tried huge quantities of newspaper or smokeless wax dipped fire lighters, sometimes I even try to reverse the downdraft with my plumbers blow torch and it can even blow that out.   Usually this drama results in a smoke filled lounge and the missus blaming me and It happens at least once a week.  
 

I have improved things with top down lighting and shed loads of smokeless fire lighters but it still wants to leave the stove via the door or the bottom vents far too often and for far too long, or it fills the whole stove up with smoke.  My installer said I need to warm the flue with cardboard but that also goes out or smokes. I generally use good dry hardwood and odd bits of softwood to get it going. 
 

I am now entertaining a negative air pressure in my house, we only have one extractor fan that’s rarely used but it seems feasible. I succefully lit it with a lounge window open today but it might have just been a good wind/temp day.  Annoyingly we can sometimes smell the burnt smell when the stove isn’t lit or going out, which is increasing my concern of negative pull from the house. Therefore my next idea is to install the external air vent supply,  as I feel like it will balance the stove and coldness in the flue.    Does this sound like a good idea?  Are there any disadvantages to the external air supply?  It looks like the arc5 uses a 65mm id pipe. 
 

Any opinions appreciated. 
 

GT

[slim reaper]

What cowl did you try, a Stainless steel “H” cowl, Ive never known one fail. Ill try and find youtube link to two I have on my house . 

 

 

 

Edited January 2, 2021 by slim reaper
links to vids

[PhillH]

Hi@Gtflash I have the exact same problems, I called the supplier of the flue and he told me a anti down draft cowl would not help and to install a vent behind the stove but not link it directly. He also told me that cold air is more dense that hot air and that is why the house fills with smoke. I usually build the fire and then spray with cleaning products or polish (something not too flammable) before lighting so it ignites fast and warms the flue quick. Leaving the stove door slightly open and a house window or door open does help to. I was told to open the stove vents at night time so the fire is not suffocated otherwise the fumes come into the house and sets of the CO alarm.

 

We also get the smell of smoke in the house on a cold day / morning due to the dense air in the flue.

 

Do you also get smoke in the house when you open the stove door if it is lit?

 

 

 

[Gtflash]

Hi @PhillH

My installer said twin wall external chimneys can be tricky and I am still of the opinion the dense cold air is forming a cold plug of air that the heat can’t pass through. 
 

if it is lit and I open the door to refuel, I don’t notice any smoke leave into the room, however I’ve just been out to the kitchen for a rum and coke and you can smell the aroma of burning stuff mildly when you come back into the room.   Never had a log burner before so don’t know if that’s normal. 

[Gtflash]

14 hours ago, slim reaper said:

What cowl did you try, a Stainless steel “H” cowl, Ive never known one fail. Ill try and find youtube link to two I have on my house . 

 

 

 

This is the same cowl but not my house.  Unfortunately I missed the fitting so don’t know what make or how it works   

[slim reaper]

Can you post a pic of your flue and roof preferably with the smoke coming out, any trees or. buildings higher than it close by.

Presumably this was a certified install ,did they test the flue for draw?

Edited January 3, 2021 by slim reaper

[Gtflash]

On 02/01/2021 at 20:31, slim reaper said:

What cowl did you try, a Stainless steel “H” cowl, Ive never known one fail. Ill try and find youtube link to two I have on my house . 

 

 

 

This is the same cowl but not my house.  Unfortunately I missed the fitting so don’t know what make or how it works   

[Gtflash]

It was dark before I lit it today.  This is the original installation pictures.  Yes all certified and smoke test done In July.  The large conifer trees look quite small in the picture.  They were topped in the summer but still shadow the house and around 8m behind the house possibly. 

[slim reaper]

If thats the cowl you have,the one in the last pic ,its just a rain hat and totally useless for downdraft.Is the flue higher than the ridge?

Edited January 4, 2021 by slim reaper

[Stubby]

9 hours ago, Gtflash said:

It was dark before I lit it today.  This is the original installation pictures.  Yes all certified and smoke test done In July.  The large conifer trees look quite small in the picture.  They were topped in the summer but still shadow the house and around 8m behind the house possibly. 

I would say that does not go past the ridge enough .