If your VC Merrimack uses too much wood

[BrotherBart]

Yep. Bad advice that we don't need here. How to turn a stove paid a lot of money for into a 55 gallon burn barrel.

In virtually every case excessive burn is from excess primary, not secondary air. If you want to mess with partial blocking, do it at the primary inlet/inlets or air wash inlets.

 

[bholler]

Here is how you take the secondary air tubes out of action. It takes an hour or two. You can possibly do this without moving your Merrimack and without disconnecting the flue, but it will be easier if you can move it forward for clearance or disconnect the flue and slide it out half-way for easier access.

Process overview: Remove the surround, loosen the top shroud, loosen the outside shroud, flex it back to reach the air intake for the secondary air tube, plug the air intake opening. Do the other side. Done.

Since you are providing these instructions are you willing to take the liability for what happens if people follow them? There are much better ways to limit draft than completely disabling the secondary combustion system

 

[Das Jugghead]

I'm tempted to try this myself, only the baffle is held up in my insert by the tubes!

Post # 26 top of the page:

Pleasant Hearth WS-2417 install/challenges/questions/observations

Today I finally got around to finishing up the secondary tubes. I found stainless steel nuts at my local Lowe's and they fit perfectly. Taking my time and performing other random chores as I went it took me just about an hour to do. Here are the nuts with information: Since they were only...

www.hearth.com

 

[stovelark]

I am constantly amused by people who always have a "better design" than the builders of a product. You really aren't doing anyone any favors by prompting them to do something in a manner in which it was not designed to be used. The Merrimack is a wonderful burning stove, as its designed. You can't get something for nothing- if you are cutting air off, you are using less fuel because you are putting out less (potentially gathered) heat from the appliance. In the event of an issue, I hope you don't try explaining that mod you did to an insurance adjuster... And for the gas discussion- Here on the east coast in new england, Jotul and Mendota, Kozy heat all suggest you use Constant pilot for the cold months of winter to keep the chimney warm and for higher reliability of ignition. Just saying-

 

[SculptureOfSound]

im not for willy nilly mods but the truth is why wouldnt you think that some mods in some cases would perform better than the original design? the original design has to meet epa specs on a specific chimney setup that may be VERY different than the end users. surely compromises are made in the design so that it performs to epa spec in one setting, and it may perform wildly different in other settings. it would be something like an oldschool engine but the user provided his own carburetor.

anyhow, i modded the tubes in my Montpelier. i didnt block them entirely but instead reduced air through them by 50-75% and i no longer have an unco trollable stove that wants to overfire. i get way longer burns AND more usable heat because my stack temps are now normal, not super hot, which means more heat in the room and not up the chimney.

besides its a bit hypocritical to be against all mods but ok with suggesting dampers in certain installs. what is a damper if not a mod?

 

[Easy Livin’ 3000]

I am constantly amused by people who always have a "better design" than the builders of a product. You really aren't doing anyone any favors by prompting them to do something in a manner in which it was not designed to be used. The Merrimack is a wonderful burning stove, as its designed. You can't get something for nothing- if you are cutting air off, you are using less fuel because you are putting out less (potentially gathered) heat from the appliance. In the event of an issue, I hop Ie you don't try explaining that mod you did to an insurance adjuster... And for the gas discussion- Here on the east coast in new england, Jotul and Mendota, Kozy heat all suggest you use Constant pilot for the cold months of winter to keep the chimney warm and for higher reliability of ignition. Just saying-

I actually admire people's ingenuity and ability to improvise, and possibly improve. You remind me of some corporate managers I've had over the years.

And, while I defer to the folks here who say that disabling the secondary system is a bad idea, most have actually also offered ways to achieve aftermarket diy improvements rather than belittling some possibly (probably) misguided ideas about how to achieve a better result in their specific situation.

The recent situation at Boeing is a case in point. One of the preminant engineering firms in the world, ever, put out their new flagship product with much fanfare, one that would be carrying millions of people, thousands of feet in the air, with bad (fatal) design flaws.

All progress is achieved by someone looking at something, and saying, I can improve this. They are not always right. But often they are.

Plus, we are talking about a Vermont Casting stove here. They have not, in more recent times, been known for their flawless design execution.

 

[bholler]

im not for willy nilly mods but the truth is why wouldnt you think that some mods in some cases would perform better than the original design? the original design has to meet epa specs on a specific chimney setup that may be VERY different than the end users. surely compromises are made in the design so that it performs to epa spec in one setting, and it may perform wildly different in other settings. it would be something like an oldschool engine but the user provided his own carburetor.

anyhow, i modded the tubes in my Montpelier. i didnt block them entirely but instead reduced air through them by 50-75% and i no longer have an unco trollable stove that wants to overfire. i get way longer burns AND more usable heat because my stack temps are now normal, not super hot, which means more heat in the room and not up the chimney.

besides its a bit hypocritical to be against all mods but ok with suggesting dampers in certain installs. what is a damper if not a mod?

Why not don't correctly and limit the draft so it is within spec? Then the stove will work as designed

 

[SculptureOfSound]

Why not don't correctly and limit the draft so it is within spec? Then the stove will work as designed

I'd gladly have installed a damper if it was feasible, button an insert it usually isn't. I can't believe stoves aren't designed with an adjustable air intake that could be calibrated to the draft....it could be set up once at install based on average draft measured. That would actually allow the stove engineers to have things run the way they designed across all installs.

As it is now, they are really only designing half of the "full combustion package" as they have no control over the chimney their stove will be attached to.

 

[begreen]

im not for willy nilly mods but the truth is why wouldnt you think that some mods in some cases would perform better than the original design? the original design has to meet epa specs on a specific chimney setup that may be VERY different than the end users. surely compromises are made in the design so that it performs to epa spec in one setting, and it may perform wildly different in other settings. it would be something like an oldschool engine but the user provided his own carburetor.

anyhow, i modded the tubes in my Montpelier. i didnt block them entirely but instead reduced air through them by 50-75% and i no longer have an unco trollable stove that wants to overfire. i get way longer burns AND more usable heat because my stack temps are now normal, not super hot, which means more heat in the room and not up the chimney.

besides its a bit hypocritical to be against all mods but ok with suggesting dampers in certain installs. what is a damper if not a mod?

Under certain limited conditions, sometimes a modification is necessary. However, they are not a universal panacea and should not be undertaken when there is a solution that does not affect the stove's ability to burn cleanly. Sometimes, it is the burning habit of the operator that is at fault and not the stove, though often this is not acknowledged. As pointed out, if nothing works then it is preferable to reduce primary air before modding the secondary air.

A damper is not a stove modification. It is a modification of the flue system to get draft in spec.

 

[jetsam]

Sending half the fuel up the flue instead of burning it is not exactly the best way to get more from your wood, either.

 

[bholler]

I'd gladly have installed a damper if it was feasible, button an insert it usually isn't. I can't believe stoves aren't designed with an adjustable air intake that could be calibrated to the draft....it could be set up once at install based on average draft measured. That would actually allow the stove engineers to have things run the way they designed across all installs.

As it is now, they are really only designing half of the "full combustion package" as they have no control over the chimney their stove will be attached to.

I have installed several dampers on inserts it can be done you can also down size the liner or restrict the liner in other ways. Of course the stove manufacturer is only designing the stove. It is the installers job to make the chimney work within that stoves specs.

 

[stovelark]

I do agree belittling anyone is wrong- if it sounded like I was doing that, I apologize. I'm just cautioning against any modification that may have to be explained why it was done if ever questioned. I wholeheartedly support always staying on the safe side of stove operation. I can say from my installation and operational experience, the Vermont castings tube stoves that I've used (the Montpelier, Merrimack and Madison) those stoves are the only VC's I would want to have in my own home. The blowers for years were suspect on the Mont and M-mack, I do believe the newer versions have improved on that issue. The Madison meant to compete with Jotul's Oslo, never took off in the US being a side loading, air tube stove. VC folks like their top-loaders!

 

[jetsam]

I don't think anyone's saying that shutting off secondary air is unsafe in and of itself. They're saying that it shuts off the secondary air, which cuts the efficiency of the stove in half.

I think some of the reaction is coming from the fact that this could actually be dangerous for a non-technical (or just new) burner who thinks, "wow, great, now my stove can go low and slow", and they smolder entire loads over 10+ hours with no secondary combustion. Being a new burner, maybe they call someone else to inspect and sweep once a season. This person is at high risk of a serious chimney fire.

 

[ABMax24]

I think there are some justifications for modifying the secondary air system on a wood stove. Overdraft due to excessive chimney height being one of them. I know that a flue damper could be installed to help curb this, but I don't like a solution that relies solely on the operator to set. Using some kind of restrictor or orifice plate in the secondary system seems like a much more fool proof way, particularly as a way to limit air to prevent over-firing.

I'm in the process of doing this on my stove, trying to bring my secondary tubes back into spec with 35ft of chimney pulling draft on the stove. The manufacturer of my stove is able to help with this situation but I'm not a fan of their fix, I believe it is far more restrictive than necessary and also requires a lot of trial and error to get to work. What I've done is mathematically calculate the orifices required to be pushed into the secondary tubes to restrict the airflow to what it would be with a standard height chimney.

 

[Jan Pijpelink]

As a scientist, I am very opposed to make any modification to an instrument/appliance for what is was designed for.
The people who have designed the appliance, a stove in this case, know what they were doing.

As @bholler mentioned, making an adjustment to an accessory (putting in a damper in the stove pipe) has nothing to do with the design or performance of the appliance it self.

Changing the design of the stove, changes the performance (maybe), but also increases the risk of malperformance, danger and risk of becoming a hazardous appliance.

 

[Nigel459]

I have been very interested in this discussion. I have now run a few modern stoves on a few very different stacks and have observed extremely different behaviour from the same stove.

I fully agree with the suggestion that the stove/chimney system should be calibrated upon installation. Ideally by an adjustment to the lowest air setting on the air control. Since that doesn’t happen, a flue damper seems to be the easiest way but this still puts onus on the operator to remember an extra lever.

It’s a thing of beauty when a stove runs as it should. It’s an exercise in frustration when draft is too strong and the end user gets to fiddle around with modifying an expensive stove that was tested and calibrated under different conditions.

Kudos to installers who test draft and consider it during the install. In the three professional installs I’ve been involved with, not one commented on or measured draft. All different companies...

 

[john26]

After looking at the manual it does look possible to install a damper directly above the appliance adapter or possibly in the adapter depending on installation. A hole would have to be drilled through the surround for the damper rod. Personally I would much rather have a damper and a rod to contend with than no secondaries.

 

[firefighterjake]

My brother was once convinced that he could build replacement parts for his Yamaha snowmobile that would be better than OEM replacements . . . funny thing about those wooden "bogie" wheels he made . . . they didn't last more than a mile or two down the trail.

 

[ABMax24]

My brother was once convinced that he could build replacement parts for his Yamaha snowmobile that would be better than OEM replacements . . . funny thing about those wooden "bogie" wheels he made . . . they didn't last more than a mile or two down the trail.

If you want to talk snowmobiles, modifying the secondaries for overdraft is more like re-jetting a carburetor for elevation.

 

[Easy Livin’ 3000]

After looking at the manual it does look possible to install a damper directly above the appliance adapter or possibly in the adapter depending on installation. A hole would have to be drilled through the surround for the damper rod. Personally I would much rather have a damper and a rod to contend with than no secondaries.

There are one or two old threads about dampers in insert situations. Definitely can be done, and way preferable to messing with the secondaries.

I was all set to try it out, and then discovered that (partially) blocking off the outside air knock-outs slowed the overdraft enough for my purposes. I went from having trouble getting 4 or 5 hours from a solid load, to 9 or 10. The sheet metal is invisible to all but me, and couldn't be simpler to execute. So much more heat is staying in the house.

The stove is great, but is was designed for a different situation than exists in my living room. After much thought, the simplest solution worked, with almost no effort.

 

[SculptureOfSound]

i should add a few points:

one i dont think completely disabling secondaries is wise or needed. Modifying them by reducing air through the tubes was something i could fiddle with and experiment to get the best burn in my situation. i didnt do it "for fun" but because my stove would overfire with the air all the way closed even if i would completely close the air after only 15 mins on a cold start.

dampers arent always possible or practical. no way i could install a damper as i have a rigid oval stack, the only round portion of the liner is the round to oval adaptor.

the idea that all stove designers know what they are doing and all stoves are designed as well as they could be (across all different draft situations) is laughable. for one, if this was true then most of the posts on this board wouldnt be needed. we wouldnt have "neverburn" as a term. designers wouldnt be needing to redesign their stoves for 2020. im not saying the average burner can design a stove better than these companies, but what we are talking about isnt designing a stove but an input modification to one of the few parameters we have access to, in my case, to make my situation safer.

 

[Easy Livin’ 3000]

i should add a few points:

one i dont think completely disabling secondaries is wise or needed. Modifying them by reducing air through the tubes was something i could fiddle with and experiment to get the best burn in my situation. i didnt do it "for fun" but because my stove would overfire with the air all the way closed even if i would completely close the air after only 15 mins on a cold start.

dampers arent always possible or practical. no way i could install a damper as i have a rigid oval stack, the only round portion of the liner is the round to oval adaptor.

the idea that all stove designers know what they are doing and all stoves are designed as well as they could be (across all different draft situations) is laughable. for one, if this was true then most of the posts on this board wouldnt be needed. we wouldnt have "neverburn" as a term. designers wouldnt be needing to redesign their stoves for 2020. im not saying the average burner can design a stove better than these companies, but what we are talking about isnt designing a stove but an input modification to one of the few parameters we have access to, in my case, to make my situation safer.

Very well put, SoS.

 

[shoot-straight]

in late to this one- but as others have suggested i think its a draft issue. too much.

i will also pile on with others and say that making such changes to a modern stove is not a good idea.

 

[begreen]

There are caveats to any approach. If a flue damper is not possible or very difficult then I would consider choking down the liner at the top of the chimney to 5" with a reducer. And if that doesn't work, then reducing the primary air first before reducing the secondary air.

Florida Bungalow Syndrome

 

[brenndatomu]

Stove manufacturers would do us all a big favor if they would clearly publish the optimal draft range required for the stove to run properly...some do plainly state it, but all too often it seems to be top secret.