Vermont Castings Aspen C3 2022

[Todd]

Hey @30WCF your posts and data are amazing. I'm dealing with the Aspen C3 taking off on me even on the break-in fires. Second break in fire it got to 825-850 F -- hoping I didn't break anything by getting it that hot on just the second fire. Yesterday, fire #5 or 6, it really took off and my laser thermometer that maxes out around 860 showed "OH"; I didn't get my IR gun to see exactly how hot it got. After maybe 30 min, it was back down to 850 or so. Last night I loaded it pretty full of oak, maybe 1-2 smaller branches of yellow poplar (oops).

I need to take a look at the intake flap and chain; I might change it by a link or two to see if that helps.

I wanted to ask if you feel confident about this being true? Do you still feel that too much air under the logs is a big part of what's happening when the stove temps run especially high?

How tall is your chimney? Could be draft is too strong.

 

[mycelianhollow]

How tall is your chimney? Could be draft is too strong.

Good call; the stovepipe+chimney is total about 24-25' (45º A-frame-ish roof). Do you think the draft could be so strong that moving it a link or two wouldn't work? (And if so, does that mean it's time to think about something like a manual damper on the outside air intake? I've wondered about that as a solution too.)

 

[Todd]

Good call; the stovepipe+chimney is total about 24-25' (45º A-frame-ish roof). Do you think the draft could be so strong that moving it a link or two wouldn't work? (And if so, does that mean it's time to think about something like a manual damper on the outside air intake? I've wondered about that as a solution too.)

I was thinking stove pipe damper first before messing around with the air. These stoves were tested on the equivalent of a 15’ chimney with perfect draft. 25’ is pretty tall and probably sucking like a Hoover at times.

 

[mycelianhollow]

I was thinking stove pipe damper first before messing around with the air. These stoves were tested on the equivalent of a 15’ chimney with perfect draft. 25’ is pretty tall and probably sucking like a Hoover at times.

VC says the Aspen C3 was not meant to be used with a stovepipe damper. I'm not inclined to give them a reason to void my warranty or anything like that. 🙁

 

[Burnin Since 1991]

VC says

I believe it's the EPA that says don't use a flue damper with a Cat stove. I looked at the Vermont Castings • Encore Model 2040-CAT-C Installation Manual_R15 • 06/25. On Page 13, when reading about chimney height and drafting issues.

In that case, the unit may experience short burn times, difficulty controlling the burn rate of the stove and the potential for overfiring. In the past, stack dampers could be recommended in these installations, but manufacturers are no longer permitted to specify these on EPA Certified models. The chimney system should be carefully reviewed and draft tested (if possible) prior to installation of this unit.

I don't know what they specified in other install manuals, but in this one they never say you "can't".
Maybe someone with more knowledge on the subject might be able to explain why the EPA doesn't want a flue (or as VC called it) "stack" damper being used with a catalytic stove certified to 2020 standards.

I'm going to guess, since it's the EPA, it is that it likely increases emissions.

I've been using a flue damper in my non-cat woodstove for a long time. I will tell you that when partially closed it increased my burn times and if used properly, I don't see any smoke coming from the chimney, just like if it was open.

Curious what others with VC stoves have in their install manuals.
Edit: I realize the Aspen and Encore are different stoves, but all I have is the Encore manual as reference.

 

[mycelianhollow]

I believe it's the EPA that says don't use a flue damper with a Cat stove. I looked at the Vermont Castings • Encore Model 2040-CAT-C Installation Manual_R15 • 06/25. On Page 13, when reading about chimney height and drafting issues.

In that case, the unit may experience short burn times, difficulty controlling the burn rate of the stove and the potential for overfiring. In the past, stack dampers could be recommended in these installations, but manufacturers are no longer permitted to specify these on EPA Certified models. The chimney system should be carefully reviewed and draft tested (if possible) prior to installation of this unit.

I don't know what they specified in other install manuals, but in this one they never say you "can't".
Maybe someone with more knowledge on the subject might be able to explain why the EPA doesn't want a flue (or as VC called it) "stack" damper being used with a catalytic stove certified to 2020 standards.

I'm going to guess, since it's the EPA, it is that it likely increases emissions.

I've been using a flue damper in my non-cat woodstove for a long time. I will tell you that when partially closed it increased my burn times and if used properly, I don't see any smoke coming from the chimney, just like if it was open.

Curious what others with VC stoves have in their install manuals.
Edit: I realize the Aspen and Encore are different stoves, but all I have is the Encore manual as reference.

Aspen C3 isn't a cat stove. I assumed VC doesn't want people using a flue damper because they designed the C3's auto air damper with specific assumptions and want to minimize variations from those.

 

[30WCF]

I do think the main runaways I have are from loosely stacked wood or a hot reload that burns the coals out from under the fresh wood and it doesn’t settle. There are exceptions and it’s hard to put a finger on all of them, but primarily, if I open the door and settle the logs, it sits down.

I do use an intake and /or flue damper at times, but that is only on occasion.

Right now we’re sitting at 600’ish for a while now with oak and gum.

 

[mycelianhollow]

I haven’t been able to really experiment cuz I’m waiting for parts to install a heat shield around the stove (walls are getting too hot), but one pattern I think I’m seeing is the stove gets hottest when I use a fast burning wood like yellow poplar (sounds random but a lot of my most seasoned wood right now is yellow poplar). I can only do 1-2 good sized splits of poplar. But if I’m burning oak I can fill the box and it doesn’t seem to run away.

I do think the main runaways I have are from loosely stacked wood or a hot reload that burns the coals out from under the fresh wood and it doesn’t settle. There are exceptions and it’s hard to put a finger on all of them, but primarily, if I open the door and settle the logs, it sits down.

I do use an intake and /or flue damper at times, but that is only on occasion.

Right now we’re sitting at 600’ish for a while now with oak and gum.

View attachment 341981

 

[30WCF]

Dumb Cat

 

[skitten]

Our cat sleeps under it.

 

[30WCF]

Our cat sleeps under it.
View attachment 344903

That’s some neat looking brick…and a purdy cat.

 

[30WCF]

I picked up a choke cable and some extra ceiling fan chain on the way home today. I have an idea to make a bypass for the spring when I want to add air to the coals, and when the cable is pressed in, the auto damper will function as designed.
Just something to play with and see. FAFO at its finest.

Maybe a throttle cable with the horizontal throw is better than the plunger. I may try both.

 

[wjohn]

Have you looked at the older (pre-C3) versions of the Aspen? They had a sort of override/biasing mechanism to do what you are wanting to do. Not that any of those parts would fit, but it would be another design to look at for ideas.

 

[30WCF]

I have not seen that. I may dig around and see what that looked like.

 

[wjohn]

I know you will find these on your own but this may speed up your search a tad. If I understand correctly, you are just biasing the bimetallic coil/thermostat one way or the other - and lengthening or shortening the chain in that moment, while still allowing the thermostat to close down the air more as it heats up.

I think that would be the ideal way to do it vs. just manipulating the intake damper directly, like we are doing. It would require some non-sanctioned modifications to the mechanism at the back of the stove.

I have never owned a 1920 but I would suspect in the "High" burn rate lever setting, it was set to crack the intake damper very slightly open even if the thermostat was fully heated up? I'd be curious to know how much. I have thought about this a lot the last few years, especially when burning dry old mulberry as it seems to need just a tad more air than the Aspen C3 will give it with a fully closed intake damper in order to keep a good burn going. Then conversely the old dry American elm will absolutely take off before the damper gets a chance to close down. Being able to bias the thermostat either way would help with this.

Aspen 1920 Manual

Aspen 1920 Parts Diagram

 

[30WCF]

I know you will find these on your own but this may speed up your search a tad. If I understand correctly, you are just biasing the bimetallic coil/thermostat one way or the other - and lengthening or shortening the chain in that moment, while still allowing the thermostat to close down the air more as it heats up.

I think that would be the ideal way to do it vs. just manipulating the intake damper directly, like we are doing. It would require some non-sanctioned modifications to the mechanism at the back of the stove.

I have never owned a 1920 but I would suspect in the "High" burn rate lever setting, it was set to crack the intake damper very slightly open even if the thermostat was fully heated up? I'd be curious to know how much. I have thought about this a lot the last few years, especially when burning dry old mulberry as it seems to need just a tad more air than the Aspen C3 will give it with a fully closed intake damper in order to keep a good burn going. Then conversely the old dry American elm will absolutely take off before the damper gets a chance to close down. Being able to bias the thermostat either way would help with this.

Aspen 1920 Manual

Aspen 1920 Parts Diagram

View attachment 345738 View attachment 345739

I think I’m planning to attempt the opposite, and create a bypass for the damper for the coaling stage, and then on reload, set it back to normal operation.
I’m not upset with how it runs when you are asking it to run, so I don’t want to mess with 87% of the cycle. It’s the last 13% that if not managed with air and pine will hold a 6” coal bed for 10 hrs without throwing any good heat.

Now, I have a good work around with pine, and sometimes I crack the door on a coal bed to help it along, and I was fine with that until @meagloth started asking questions, it sparked the interest of the tinker in me again.

The system you describe @wjohn, sounds like a way to introduce a little extra air into the stove when it’s closed due to a reasonable fire temperature, but I think what I want is to fully open the damper when it coals up, and then let it do business as usual when it’s burning the whole logs again.

I was thinking of adding a short section of chain, maybe 1.5-2” to the damper, the use the cable to lift that chain when I want to open the damper, and when the cable is retracted the short piece of chain will just be slack, with not much added weight, and the coil should lift and lower the damper as designed.

Now, I don’t know that this is actually any better than cracking the door or tossing pine on unless you are worried about draft reversal and CO., because either of them works just fine for me now.

This also has the potential to be like the time I forgot about the pencil I shoved in the intake damper and left the house after a reload. Burned a full load of wood with no damper in place that day. But most other stoves there is some amount of external controls, and the reason I forgot about the pencil was because who shoves a pencil in the damper? I mean the reason was because I haven’t had to think about or manipulate an external control for 3 years. So I think I would just re-learn if it had one.

Getting a little long winded here, but I have plenty of slack in the chain when the stove is rolling. That chain has a service loop in it when it’s running 800STT. So I could shorten the chain by 3/4” and still have it close, and also have it open at a lower temperature than it is currently opening at, but…but will that hold the air open too long before it shuts down a good off gassing?