Catalytic stoves v Secondary Air

[neiln]

4 hours ago, Witterings said:

 

Reminds me of a story, my boy's at Uni so no money, took his old Seat Ibiza in for an MOT a couple of years ago (couldn't get booked into the place I normally go to and trust) and the garage said it  had failed on emissions and would be £750 to repair.

I rang the place I normally go to for a comparative quote and they said drop the car into us ..... they took it for "An Italian Tune Up" just before another MOT and it passed and has done for the subsequent 2 years without having anything being done to it 🙂  .... the garage I trusted did make the comment "Kevin up to his old tricks again is he".

 

Back on topic .... if it produces heat from a smouldering log I'm guessing there's no real flame but is also what contributes teh long burn times ??

Personally whilst it's obviously used for heat I love the esthetics of a decent flame, wouldn't quite be the same without if the logs were just smoldering away n teh box but maybe I've misinterpreted it?

 

 

Correct.  When set low the glass will also blacken, so there's absolutely nothing to see.... It's an efficient and simple wood heater not something for ambience

[neiln]

To respond to your earlier question witterings, a cat stove isn't any more efficient than a secondary air stove but because of the whole house system and the way users run them, cat stove owners often report using less wood.... Or rather owners of stoves with secondary air report burning much more than their old stove did.   Remember, a lot of stove users in the US are in cold winter climates and the stove is their primary heat.  They want ease of use.  They often light them and run them continuously for months. Secondary air stoves can't be run that low and owners will open windows on milder days, plus the house will be toasty warm all day even if the owner is out at work, and all night when tucked in bed (under just a light sheet).  The cat stove other has the convenience of constant heat but turns it really low when out, asleep or mild.

[openspaceman]

1 hour ago, neiln said:

owners of stoves with secondary air report burning much more than their old stove did.

It's not really secondary air, it's a way of getting hot excess air in to (nearly) guarantee a burn out. Looking at the video earlier in the thread comparing stoves  this extra excess air ( there is always some excess, unused oxygen in the secondary air)  being introduced probably increases massflow significantly, so heat is lost in this air being given a free ride and exiting at whatever temperature is left after heat exchanges to the room.

 

One benefit of the catalyst is that you can feed it nearer stoichiometric amounts of air thus minimising massflow but I', still not convinced of the cost benefit.

[Witterings]

2 hours ago, neiln said:

To respond to your earlier question witterings, a cat stove isn't any more efficient than a secondary air stove but because of the whole house system and the way users run them, cat stove owners often report using less wood.... Or rather owners of stoves with secondary air report burning much more than their old stove did.   Remember, a lot of stove users in the US are in cold winter climates and the stove is their primary heat.  They want ease of use.  They often light them and run them continuously for months. Secondary air stoves can't be run that low and owners will open windows on milder days, plus the house will be toasty warm all day even if the owner is out at work, and all night when tucked in bed (under just a light sheet).  The cat stove other has the convenience of constant heat but turns it really low when out, asleep or mild.

 

This 100% isn't doubting you in case you think it is but I honestly don't get how they get such long burn times.

 

Granted my stove is probably that much smaller and you can't get nearly as much wood in but if I got a half decent fire going and a decent bed of ash and then rammed it the gills and turned it down to as low as I could .... I'd still be having to add more wood after about 2 hours but you hear reports that these run for between 12 and some quoting 30 hours before needing to be refilled so unless they are MASSIVELY more efficient I don't get it.

 

Surely as well if you doubled the size of my stove it'd then just be burning a larger surface area of the amount of wood that's in there so again the size alone wouldn't contribute but they get as a minimum 6 x's the burn time as a minimum estimated up to 15 x's as long with the best .... I'm struggling to get my head round it I have to admit. 

[neiln]

They are MASSIVE stoves. The bk Princess is at least 4-5 times the size of yours, assuming you have a 5kw stove.  It will take 16" logs, split no more then say 8-10".  Big logs burn slower, a huge fire box takes a lot more fuel.  They really do burn a long time, the large secondary air stoves will do 8-12 hours, cat stoves 12-24 or more if right down low.  They aren't more efficient, it's the same regs.  The European regs just copy the US EPA regs a few years behind, besides our stoves are 80-85% efficient so there's not much to gain there.  It is simply more fuel in the stove.  Plus your 40 minute reloads are to keep pretty flames, the big stove long burns a "load to 'coals".  They aren't pretty looking room heaters, they are devices to heat a whole house through a cold winter easily. 

[neiln]

Go on hearth.com and read the user experiences, or any of the other mainly us forums, and you'll get a feel for how they use their stoves

[Witterings]

4 hours ago, neiln said:

They are MASSIVE stoves. The bk Princess is at least 4-5 times the size of yours, assuming you have a 5kw stove.  It will take 16" logs, split no more then say 8-10".  Big logs burn slower, a huge fire box takes a lot more fuel.  They really do burn a long time, the large secondary air stoves will do 8-12 hours, cat stoves 12-24 or more if right down low.  They aren't more efficient, it's the same regs.  The European regs just copy the US EPA regs a few years behind, besides our stoves are 80-85% efficient so there's not much to gain there.  It is simply more fuel in the stove.  Plus your 40 minute reloads are to keep pretty flames, the big stove long burns a "load to 'coals".  They aren't pretty looking room heaters, they are devices to heat a whole house through a cold winter easily. 

 

Thank you for that ... it's a really helpful explanation and yes I was totally underestimating how large they actually are and not just how much fuel they can take but also the size of it.

 

I think the Mecca in my opinion would be a stove that you could fill it so it burns for about 4 / 5 hours without a refill and still gives a flame for ambiance without being huge yet doesn't soot up the glass .... ours seems to teeter on the edge of lower flame means sooty glass.

 

As I've typed that it makes you analyse what you do, I was told leave the door open a bit and both the primary and secondary air supplies fully and as it gets going close the door 1st. 

When it's going a bit more / starting an bed of ash close down the primary fully and control the burn with the secondary but have always found I can't turn the secondary down that much without creating build up on the glass.

 

Maybe if I left the primary open a bit rather than fully closing it I could turn the secondary down further for an overall slower burn and the load may last a bit longer ... definitely worth experimenting with.

Edited March 23, 2021 by Witterings

[neiln]

If by primary you mean air from beneath the grate, and secondary air from above (often air wash down the glass) then most wood burning stoves are cleanest burning and keep the glass clean with the primary shut and secondary controlling the stove.

 

Your Mecca stove would be fabulous but wood isn't dense enough to pack l enough energy in to a small firebox. 

[Witterings]

3 minutes ago, neiln said:

If by primary you mean air from beneath the grate, and secondary air from above (often air wash down the glass) then most wood burning stoves are cleanest burning and keep the glass clean with the primary shut and secondary controlling the stove.

 

Your Mecca stove would be fabulous but wood isn't dense enough to pack l enough energy in to a small firebox. 

 

Yes primary / secondary as you describe.

 

It'd be a really interesting project to have 2 absolutely identical approx 5kw stoves built in terms of sizing / materials used etc. except for one built using secondary air and the other fitted with a cat and compare efficiency / burn time etc. and if the catalytic version produced any flame or not.

 

If it's just a big thing that sits there with no flame / ambiance that only serves to produce heat you may as well have a pellet fueled boiler (or any other more efficient system) placed somewhere it can't be seen and a smaller stove where you want the esthetic appearance.

 

We only had our burner fitted in October 2019 mainly for the esthetics / ambiance although we paid about £250 for wood the 1st year and knocked £400 off our normal heating bill.

I scrounged / cut and seasoned my own wood for this year so have saved £400 on the most recent bill and enjoyed something that has made lockdown over a winter period a lot easier to deal with ... take the dogs out for a walk on a cold winters afternoon, come home and light the fire and read a book / catch up on forums for a bit in front of ithe fire with an early beer and then cook / eat some dinner and watch a film in front of it ... life doesn't get much better than that 🙂 ... although it will be nice to see more of friends again.

 

Feel like I've hijacked the OP's thread a little bit and hat was never my intention but hopefully some of the questions I've asked and answers I've had may be useful to them as well and a big that you @neiln ... you been really helpful!!

 

  

 

 

[Billhook]

7 hours ago, Witterings said:

 

Yes primary / secondary as you describe.

 

It'd be a really interesting project to have 2 absolutely identical approx 5kw stoves built in terms of sizing / materials used etc. except for one built using secondary air and the other fitted with a cat and compare efficiency / burn time etc. and if the catalytic version produced any flame or not.

 

If it's just a big thing that sits there with no flame / ambiance that only serves to produce heat you may as well have a pellet fueled boiler (or any other more efficient system) placed somewhere it can't be seen and a smaller stove where you want the esthetic appearance.

 

We only had our burner fitted in October 2019 mainly for the esthetics / ambiance although we paid about £250 for wood the 1st year and knocked £400 off our normal heating bill.

I scrounged / cut and seasoned my own wood for this year so have saved £400 on the most recent bill and enjoyed something that has made lockdown over a winter period a lot easier to deal with ... take the dogs out for a walk on a cold winters afternoon, come home and light the fire and read a book / catch up on forums for a bit in front of ithe fire with an early beer and then cook / eat some dinner and watch a film in front of it ... life doesn't get much better than that 🙂 ... although it will be nice to see more of friends again.

 

Feel like I've hijacked the OP's thread a little bit and hat was never my intention but hopefully some of the questions I've asked and answers I've had may be useful to them as well and a big that you @neiln ... you been really helpful!!

 

  

 

 

As the original poster,  I always  value the way these threads develop and I have learned a lot thank you all.