"Sweet spot" & cat stoves

[Diabel]

Should I be able to turn the primary air on my defiant completely?

I noticed that if I have the primary air open (by-pass closed) 1/4 way the cat glows quite a lot & lots of flame in the firebox, griddle temp will be around 650-700*, internal flue 24" up will be around 400-450*. If I turn it to 1/2 closed position cat stops glowing & flames become lazy & slow, griddle temps will drop to 550-600* & flue temp will stay around 400*. If I close the primary air completely flames disappear I can see a faint glow from the cat (hardly noticeable), griddle temp will drop to 450-500* * flue temp will start to drop as well. During all this time there is no visible smoke out the pipe (other than steam on very cold days). After about 45min on burning at fully closed primary air, I will start to see a bit of smoke out the chimney (not huge amount but surly noticeable). This tells me that cat operation has stalled....
Is this possible?

Also, if at this point I open the primary air to 1/2 some flame re-appears & the smoke disappears from the chimney.

My wood supply is pretty dry 2-3yr old beech split back then. To the point that if I run the stove on open by-pass there is "0" smoke out the pipe!

 

[henkmeuzelaar]

Should I be able to turn the primary air on my defiant completely?

I noticed that if I have the primary air open (by-pass closed) 1/4 way the cat glows quite a lot & lots of flame in the firebox, griddle temp will be around 650-700*, internal flue 24" up will be around 400-450*. If I turn it to 1/2 closed position cat stops glowing & flames become lazy & slow, griddle temps will drop to 550-600* & flue temp will stay around 400*. If I close the primary air completely flames disappear I can see a faint glow from the cat (hardly noticeable), griddle temp will drop to 450-500* * flue temp will start to drop as well. During all this time there is no visible smoke out the pipe (other than steam on very cold days). After about 45min on burning at fully closed primary air, I will start to see a bit of smoke out the chimney (not huge amount but surly noticeable). This tells me that cat operation has stalled....
Is this possible?

Also, if at this point I open the primary air to 1/2 some flame re-appears & the smoke disappears from the chimney.

My wood supply is pretty dry 2-3yr old beech split back then. To the point that if I run the stove on open by-pass there is "0" smoke out the pipe!

I just happened to have studied the operation of the VC Defiant and the VC Encore cat stoves for another thread when I saw your post.

According to the current manuals, you can't actually CLOSE the primary air flow by moving the handle on the right side of the oven all the way towards you, but just will put it in the "low" flow position.

Only the bypass flow (left-side handle) can be fully closed.

When I try to follow your description, though, I get a little confused: when you say "primary air open 1/4 way", do you mean that the handle has been moved 1/4 of the way forward (from its high flow position in the back) or 1/4 backwards (from its low flow position in the front?

What you call "I/2 way closed" seems fairly unambiguous; i.e. simply midway between the two extreme positions and what you call "close completely" would seem to mean all the way towards the forward, low flow position. Please confirm nonetheless, so we don't end up talking past each other.

Once I am completely clear I understand you properly I promise to try and analyze what might be happening.

Henk

 

[Diabel]

Thanks Henk,

Yeah, I thought I was clear...but I think only in my little head! 1/2 closed I mean primary air (handle on the right hand side facing the stove) looks straight down. And the 1/4 is 1/2 way between fully open & 1/2 open.....does this make sense?
Thanks

 

[HotCoals]

I can dial back as low as I want after re loading and I'm up to temp,cat will glow for 4 or 5 hours easy.
If I'm on one I might have only 350-400 stove top near cat though..but even then it does a good job.

 

[Todd]

Yes it's possible for the cat to stall. How soon are you closing her down? I like to give my cat a good 20 minutes with some flame before turning it down for a low burn.

 

[henkmeuzelaar]

Should I be able to turn the primary air on my defiant completely?

I noticed that if I have the primary air open (by-pass closed) 1/4 way the cat glows quite a lot & lots of flame in the firebox, griddle temp will be around 650-700*, internal flue 24" up will be around 400-450*. If I turn it to 1/2 closed position cat stops glowing & flames become lazy & slow, griddle temps will drop to 550-600* & flue temp will stay around 400*. If I close the primary air completely flames disappear I can see a faint glow from the cat (hardly noticeable), griddle temp will drop to 450-500* * flue temp will start to drop as well. During all this time there is no visible smoke out the pipe (other than steam on very cold days). After about 45min on burning at fully closed primary air, I will start to see a bit of smoke out the chimney (not huge amount but surly noticeable). This tells me that cat operation has stalled....
Is this possible?

Also, if at this point I open the primary air to 1/2 some flame re-appears & the smoke disappears from the chimney.

My wood supply is pretty dry 2-3yr old beech split back then. To the point that if I run the stove on open by-pass there is "0" smoke out the pipe!

Yes, as already mentioned by previous responder(s), the cat can certainly "stall" if you are no longer manually providing enough primary flow.

Although well-designed cat stoves are in principle able to let the secondary flow through the cat be completely regulated by a thermostatic valve, there are so many differences in stack draft, site altitude, load size, wood quality, cat condition etc. that it is beneficial to be able to regulate the primary flow manually, as is possible on your VC stove.

Some stoves with very strong drafts, low altitude siting, small loads and highly efficient cats might be able to run just fine with the primary air valve in the lowest flow position. Other stoves, such as yours, apparently require the valve to be opened further in order to sustain proper cat operation.

Henk

(edit I should have added that, if you notice that you gradually need to open the primary air valve further and further in order to keep the cat operating properly (without having changed wood type & quality or having increased load size) you might be witnessing the cat losing its efficiency. I would expect that such loss of efficiency can only be compensated by larger primary flows op to a certain point, at which the larger flows might actually start cooling the cat down.... In that situation, it is probably time to regenerate or replace the cat.

 

[Diabel]

Thanks guys!

I just might be a bit impatient & start turning it down too fast. Tonight I will let it burn for at least 20min with good flame before turning it down for the night.

 

[jimbom]

Should I be able to turn the primary air on my defiant completely?

I noticed that if I have the primary air open (by-pass closed) 1/4 way the cat glows quite a lot & lots of flame in the firebox, griddle temp will be around 650-700*, internal flue 24" up will be around 400-450*. If I turn it to 1/2 closed position cat stops glowing & flames become lazy & slow, griddle temps will drop to 550-600* & flue temp will stay around 400*. If I close the primary air completely flames disappear I can see a faint glow from the cat (hardly noticeable), griddle temp will drop to 450-500* * flue temp will start to drop as well. During all this time there is no visible smoke out the pipe (other than steam on very cold days). After about 45min on burning at fully closed primary air, I will start to see a bit of smoke out the chimney (not huge amount but surly noticeable). This tells me that cat operation has stalled....
Is this possible?

Also, if at this point I open the primary air to 1/2 some flame re-appears & the smoke disappears from the chimney.

My wood supply is pretty dry 2-3yr old beech split back then. To the point that if I run the stove on open by-pass there is "0" smoke out the pipe!

Yes, as already mentioned by previous responder(s), the cat can certainly "stall" if you are no longer manually providing enough primary flow.

Although well-designed cat stoves are in principle able to let the secondary flow through the cat be completely regulated by a thermostatic valve, there are so many differences in stack draft, site altitude, load size, wood quality, cat condition etc. that it is beneficial to be able to regulate the primary flow manually, as is possible on your VC stove.

Some stoves with very strong drafts, low altitude siting, small loads and highly efficient cats might be able to run just fine with the primary air valve in the lowest flow position. Other stoves, such as yours, apparently require the valve to be opened further in order to sustain proper cat operation.

Henk

(edit I should have added that, if you notice that you gradually need to open the primary air valve further and further in order to keep the cat operating properly (without having changed wood type & quality or having increased load size) you might be witnessing the cat losing its efficiency. I would expect that such loss of efficiency can only be compensated by larger primary flows op to a certain point, at which the larger flows might actually start cooling the cat down.... In that situation, it is probably time to regenerate or replace the cat.

What is this regenerate that you speak of? Is this the cleaning with 50% white vinegar?

 

[henkmeuzelaar]

What is this regenerate that you speak of? Is this the cleaning with 50% white vinegar?

Yes, but I think there are several logical steps in trying to regenerate/rejuvenate a catalytic combustor:

(1) I would always try to follow whatever procedure the manufacturer of the cat recommends;

(2) however, if the manufacturer does not clearly describe how to thermally pre-clean the cat before removal from the stove and I can see through the inspection hole that the cat appears dark brown or black, I would first fire my stove with high quality dry wood at the highest stove temperature I am comfortable with in order to burn off as much creosote and coke as possible;

(3) then I would carry out the manufacturer's recommended cleaning and surface treatment procedure which usually involves careful brushing off to try and open up any plugged channels (NEVER do this with high pressure air or water jets though!) followed by the 50% vinegar treatment and various rinsing steps with distilled and/or deionized water.

Note that the vinegar leaching/etching treatment cannot be expected to remove any dark creosote/coke layers or streaks which might have survived the attempt at burning off during the pre-cleaning step, particularly if the activity of the catalyst was severely reduced through poisoning (e.g. with sulfur or lead).

(4) At this point I would remount the cat (again following manufacturer's instructions) and do a couple of test runs with dry, high quality wood while observing if the cat is indeed properly working again.

In case the cat activity is disappointing after the whole regeneration process most people will probably give up and install a new cat.
Personally, however, I would then remember how industrial platinum and/or palladium cat regeration procedures often do include steam gasification as a step to remove coke.

(5) So, only in a situation like this, i.e. with nothing to lose, and particularly if the cat still shows dark coke deposit areas, I would make the stove quite hot, with a nice large bed of glowing coals, and then quickly drop a few small splits of pre-wetted high quality wood on the bed (immediately closing the door!) to force one or more shots of hot steam through the cat in the hope of gasifying off the coke.

Final note: cat manufacturers generally only recommend to try and clean/regenerate a cat if one is comfortable carrying out such a procedure. This never involves my step #5, probably because this is a more complicated procedure involving "bad stove operating procedures" (i.e. throwing in wet splits) and also perhaps because many (most?) wood stove cats do not lose activity through coking but through a combination of getting coated with ultra-fine ash particles (slagging) and/or being poisoned; both of which can in principle be remedied by the vinegar treatment. Please also note that I am certainly not recommending you carry out step #5 but just explaining what I would do (and I do lots of stupid things )

Henk

 

[jimbom]

Henk, Thanks for the reply and the information. I have seen steam burns. I will take your advice and not try this at home. Jim

 

[Diabel]

Yeah,

Thanks Hank for a very scientific explanation.

Last night I brought the stove to nice 550* temp. closed the by-pass with primary air fully open, waited 25-30min...I could see the cat area nice & orange, then I slowly shut the primary to about 80% closed. Two hrs later the cat was doing its job! No stall!! Thanks Todd.

 

[henkmeuzelaar]

Yeah,

Thanks Hank for a very scientific explanation.

Last night I brought the stove to nice 550* temp. closed the by-pass with primary air fully open, waited 25-30min...I could see the cat area nice & orange, then I slowly shut the primary to about 80% closed. Two hrs later the cat was doing its job! No stall!! Thanks Todd.

Great to hear that. Congratulations!

Just out of curiosity; do you have the VC Defiant or the VC Encore cat stove ? (your profile is a bit vague on that)

Henk

 

[tiber]

Err if this is a defiant (and I'm not sure what it is in canada), it really wants to cruise at the 500F to 600F range. I'm still paranoid given that this is my first year wood burning in my own house but I get nervous when the stove is over 600F. The overfire is listed as 750F but I couldn't imagine running this big of a stove flat out at that temp for any legnth of time without melting my eyeballs. 550F to 600F is what I observe with my Defiant 1910 (same as the current defiant but without the reversable flue).

 

[Diabel]

It is the smaller brother of the defiant. However, on its sides it says "defiant encore" I believe back 20yrs ago VC did not make the big boy yet! But I could be wrong (not the first time).

 

[Diabel]

Err if this is a defiant (and I'm not sure what it is in canada), it really wants to cruise at the 500F to 600F range. I'm still paranoid given that this is my first year wood burning in my own house but I get nervous when the stove is over 600F. The overfire is listed as 750F but I couldn't imagine running this big of a stove flat out at that temp for any legnth of time without melting my eyeballs. 550F to 600F is what I observe with my Defiant 1910 (same as the current defiant but without the reversable flue).

Mine regularly sits at 650-700* & nothing is melting yet! But then again......how much trust do we put in these cheapo thermometers!