Tertiary Air Query

[Jimmy101]

Hi All,

 

I moved into a house a year ago that has a Parkray Consort Slimline 5 installed that was left by the previous owners. I've been having some issues with it and I can't seem to find much information that relates to the specific problem I'm having online so could do with some guidance from someone who has the experience.  I have recently had the flue swept and have replaced the secondary air & glass gasket as well as the door rope seal to ensure everything is up to scratch. 

 

The manual is extremely vague on the tertiary air inlet on the rear of the stove which is controlled by adjusting a blanking plate to control the air flow. This is fixed once set and the primary and secondary air vents are used to light and control the burn.  Logic says the more the tertiary inlet is open the more oxygen gets to the fire and the logs will burn faster but if I open the tertiary air vent at all it's almost as if my wood burner starts to pull that much air in all the heat and oxygen just gets sucked straight up the flue. With the tertiary vent open the kindling burns like mad and has disappeared before the logs have even had chance to ignite. 

 

To get my fire lit properly I am also having to close the primary air pretty much as soon as the fire lighter is lit,  if I leave this open then the fire struggles to get up to temperature again as if the heat is all being lost up the flue. I found this out accidentally the other day when I lit a fire without realising I had left the primary air shut but it happened to light better than I've ever done it before. Once the fire is going I am also finding that I have very little control while using the secondary air vent. I bought some  kiln dried logs just rule out any issues with moisture content  but the secondary air vent is pretty much always fully open while in operation with any reduction in air seeming to kill the fire off quite quickly.

 

Any help would be greatly appreciated. 

 

Thanks

 

James

[neiln]

Is the baffle in place?

[Jimmy101]

1 hour ago, neiln said:

Is the baffle in place?

Yeah 

[Mik the Miller]

The tertiary air should be adjustable (?) on my Stovax it's a simple sliding plate that block off the rear inlet. Push it right in and it's shut, pull it out a few mm and there is a small gap which grows to around 100mm long by 15mm high.

 

It sound like you have a really good draw from your flue so you probably only need it to be open by a very small amount.

If you take the top baffle out and then the side/rear firebrick you should see the hole ?

If you have too much draught a draught stabiliser may be needed.

 

instruction manual

 

Edited November 21, 2020 by Mik the Miller

[Jimmy101]

15 minutes ago, Mik the Miller said:

The tertiary air should be adjustable (?) on my Stovax it's a simple sliding plate that block off the rear inlet. Push it right in and it's shut, pull it out a few mm and there is a small gap which grows to around 100mm long by 15mm high.

 

It sound like you have a really good draw from your flue so you probably only need it to be open by a very small amount.

If you take the top baffle out and then the side/rear firebrick you should see the hole ?

If you have too much draught a draught stabiliser may be needed.

 

instruction manual

 

Yeah its adjustable by loosening a bolt and then covering as much of the hole up as you choose. I can only really move it when the fire is cold due to it being on the back so its trial and error . Ive got it fully shut at the minute but may try it cracked a tiny bit to see what happens as it didnt work fully open. 

 

Im getting much better fires going following the flue sweep and replacing a gasket in the secondary air vent whicu crumbled to bits when i touched it.  Im getting a good 1h to 1h20 out of two logs and the temp is fine but it never seems to get to the point of using the secondary vent to control the burn rate. Perhaps i dont need to bother though. 

[openspaceman]

10 hours ago, Jimmy101 said:

 

The manual is extremely vague on the tertiary air inlet on the rear of the stove which is controlled by adjusting a blanking plate to control the air flow. This is fixed once set and the primary and secondary air vents are used to light and control the burn.  Logic says the more the tertiary inlet is open the more oxygen gets to the fire and the logs will burn faster but if I open the tertiary air vent at all it's almost as if my wood burner starts to pull that much air in all the heat and oxygen just gets sucked straight up the flue. With the tertiary vent open the kindling burns like mad and has disappeared before the logs have even had chance to ignite. 

 

This tertiary air, does it come into the firebox preheated and through a horizontal line of small holes at the back?

 

If so this is to prevent the fire being starved of air and avoid smouldering logs being left, it ensures enough air to maintain a flame when the fire is low.

 

I take it this is a multifuel stove? Generally dry wood does not need primary air after it is started and flaming, if at all. It's smokeless fuels that need primary air to gasify the coke to produce carbon monoxide that then burns as a flame in the secondary air.  Is there a way to shut the primary air and prevent secondary air getting under any grate? If not let a bed of ash fall through and do the job.

10 hours ago, Jimmy101 said:

 

To get my fire lit properly I am also having to close the primary air pretty much as soon as the fire lighter is lit,  if I leave this open then the fire struggles to get up to temperature again as if the heat is all being lost up the flue. I found this out accidentally the other day when I lit a fire without realising I had left the primary air shut but it happened to light better than I've ever done it before.

That's it, it has to do with mass flow, to burn a kilo of dry wood requires ~5m3, which is about 7kg, of air. The energy in the wood has to be released by oxidising it and that energy has to raise the temperature in the firebox. Adding more air to a cold fire means the firebox is constantly being cooled. Excess air and wood moisture are bad dampeners to a fire.

 

 With  the fire burning what do the jets of air out of the small holes at the back look like?

[Jimmy101]

9 hours ago, openspaceman said:

 

This tertiary air, does it come into the firebox preheated and through a horizontal line of small holes at the back?

 

 

 

I take it this is a multifuel stove? Generally dry wood does not need primary air after it is started and flaming, if at all. It's smokeless fuels that need primary air to gasify the coke to produce carbon monoxide that then burns as a flame in the secondary air.  Is there a way to shut the primary air and prevent secondary air getting under any grate? 

 

 With  the fire burning what do the jets of air out of the small holes at the back look like?

Cheers for all the info 

 

Yeah there are a row of horizontal lines at the back when fully open these looked almost as if the flame was being split by the air coming in you can see the little holes through the flames if that makes sense?

 

Yeah it's multifuel, i have a decent bed of ash ontop of the grate and there is only a small hole that air could get under. Is it just worth letting the ash pan build up to the grate and then just occasionally remove some ash from above? 

 

Its almost as if the tertiary air is providing too much to get the fire going but then once up and running the secondary isn't quite providing enough on its own at times. Some times logs burn right through and others they can smoulder a bit. Ill try the tertiary cracked a small amount today and see how it goes. 

Edited November 22, 2020 by Jimmy101

[Mik the Miller]

11 hours ago, openspaceman said:

<snip>

That's it, it has to do with mass flow, to burn a kilo of dry wood requires ~5m3, which is about 7kg, of air. The energy in the wood has to be released by oxidising it and that energy has to raise the temperature in the firebox.

 

I like detail like that ....

 

Each stove has a personality which needs to be understood to get it to burn happy. Wood fires burn from the top down, they (as @openspaceman said) don't need air coming from underneath. Once the firebox is hot enough you just need to trickle in enough oxygen/air to ignite the gasses and keep the temp up. The body of the stove passes this heat to the room so you only need to maintain the inside heat to allow this convection to take place. Roaring fires and lots of yellow flame isn't what a stove is about.

 

After a while you should be able to maintain this state for an hour or so without adding more fuel, its a balancing act. Some stoves are more tempremental than others but it's most rewarding when you find that sweet spot.

[Jimmy101]

Thanks guys, 

 

To be fair this will only be our second winter in the house so im definitely still getting used to it. Last year i made the fatal mistake of buying logs that were too wet but im definitely getting there now. 

 

I had always been closing the primary air down once lit but was thinking something seemed off by the fact it actually works better if i close it down as soon as the kindling is going rather than the logs. It didnt quite fit with what the manual suggested but I guess if it works just go with it. 

[openspaceman]

8 hours ago, Jimmy101 said:

Yeah there are a row of horizontal lines at the back when fully open these looked almost as if the flame was being split by the air coming in you can see the little holes through the flames if that makes sense?

 

This is much as mine, I have no other experience of these modern insulated firebox stoves than my Morso, when I did work with biomass boilers the smallest was 24kW and the biggest 1MW at an Ikea store.

 

The thing is that even if the jets don't appear to do anything other than split the flame they are still functioning as intended. Sometimes you will see a brighter section of flame above and around the jet, showing it is adding needed air as well as turbulence. Also consider how the air paths see to swirl in these stoves, the airwash comes down the glass and hits the burning wood at the floor then runs back across the burning wood and up the back, then forward across the baffle then exits, a near circular motion. Those jets might not find any fuel gas left in the flames  but still contribute hot excess air before it ventures up the flue.