Yes, your stove is over drafting... Blame the ...

[SpaceBus]

It should always be kept in mind the certain online retailers of catalytic combustors suggest replacing them at 12,000 hours. My local tire shop told me I should replace my Toyo $800 each tires every 20,000 miles. I have no idea why they would suggest that!

To be fair most expensive tires generally don't last past 20,000 miles, but that is due to being made from high performance compounds that just don't last long.

 

[BKVP]

After scanning this thread (which has some valid points by quite a number of posters) I have to say we are all forgetting a few important details, we're all on this forum, so we are all kinda like stove nerds to an extent, maybe not nerds but helicopter stove users lol, many of us strive to take advice from senior members and get ahead on wood supply so we can have dry premium fuel, a number of us have taken the time to learn about stove & chimney mechanic's and a few have become actual data collectors.
Remember the current tests were set and based off of Oregon testing method back in the mid 80's to provide standardization for all, as technology improves so does delivery and advantage, which can open up to new unforeseen issues that were not around during initial testing.
Back in the day if a stove was drafting harder then the minimum of .05wc not many were complaining because the stove was burning cleaner, people didnt have moisture meter available to them at a cheap price so to old bang 2 splits together to hear the ping noise was sufficient.
Times have improved so much especially after 2010 that we all, this includes our current testing have gotten ahead of ourselves, now you have a stoves that are designed to run into the mid 70's and above efficiency at the lowest possible draft of .05wc, this is a problem for the stove designer and not the regulator, we here on this forum are seeing the higher end of this problem because many of us are actually following the rules and burning dry wood, so many are hyper sensitive.
Now running around and blasting people for this issue isnt the right way of going about business, the baro dampers may work for some, but for a guy like me with a high efficiency cat stove with low flue temps to begin with, I know better then to try that, I need as much heat in my flue gasses as possible or I will have an issue (prob icicles clogging the cap) but maybe for someone with a reburn tube stove that can maintain 650 deg flue gases during the main fire stage of the burn, it could work for them, basically what I'm saying is that the general paint brush method of painting everything one color isnt the answer, testing individual chimney's is a good start, figuring the actual flue temps during a low, medium and high burn helps, knowing your stove and fuel source is the biggest.

Remember, in the method and in a lab we can control stack velocity. Our gases/emissions are dumped into a hood and do not exit in the manner a home installation occurs.

 

[BKVP]

Fair enough I didn't know that. But wouldn't installing a stove that is not withing draft specifications therefore be illegal as well? By installing a damper I am making it conform to those specifications. I completely agree modifying the stove should be against regulations. But modifying the vent with products approved for that venting system in order to meet draft specifications should not be a violation. But I could be completely wrong there.

You know, a couple of years ago a certain agency began calling hearth retailers to ask them how often they used dampers in their installations. You are very familiar with single burn rate stoves that have become more common since 2015. Well, they are not allowed to have any control mechanism to alter that single burn rate. The use of a damper in the flue can alter the burn rate.

The keys words are "as tested". No manufacturer to my knowledge tests with a flue damper....because it's not permitted in the dilution tunnel configuration. And if isn't used that way to test.....default to the first sentence.

You are VERY correct about the calculations/numbers not meaning much. The reason, variability. That will be my new buzz word for 2021!

 

[BKVP]

The T5 breathes pretty easily. So do several SBI and some Regency models. This is a function of the stove design, not an externally applied regulation.

It should also be noted that Drolet and some others specifically allow downsizing in their documentation when the flue height exceeds 25 ft. The whole thought that a key damper or downsizing the flue to reduce draft in a high draft installation is a bit silly. It would knock the use of some draft-fussy cat and downdraft stoves right off the market. A stove with a max .06" draft requirement probably couldn't be installed on a 25-30' flue without some sort of draft reduction. Yet we see them here regularly. It is this wink wink nod nod relationship that I think sadpanda is calling out. He has some facts wrong, but this grey area is real and stove mfgs. dance around it by telling owners to call in a sweep or their tech support if draft is excessive.

Not all manufacturers. We often here of stacks greater than 30' that we suggest they look at other options. When you have folks unwilling to run a liner "My clay liner has worked for over 40 years with my XXXX model"... Keep in mind that as of 2015, Owners & Operator Manuals have become Federally regulated documents. They are part of the certification process and must cover operational and installation specifications. So while some may wink wink nod nod, not here!

 

[BKVP]

To be fair most expensive tires generally don't last past 20,000 miles, but that is due to being made from high performance compounds that just don't last long.

It has nothing to do with the 3,000 lbs of wood in the back being driven over course gravel roads. Or driving to Missoula or Helena at 90 mph and having a state trooper pass you!

 

[bholler]

You know, a couple of years ago a certain agency began calling hearth retailers to ask them how often they used dampers in their installations. You are very familiar with single burn rate stoves that have become more common since 2015. Well, they are not allowed to have any control mechanism to alter that single burn rate. The use of a damper in the flue can alter the burn rate.

The keys words are "as tested". No manufacturer to my knowledge tests with a flue damper....because it's not permitted in the dilution tunnel configuration. And if isn't used that way to test.....default to the first sentence.

You are VERY correct about the calculations/numbers not meaning much. The reason, variability. That will be my new buzz word for 2021!

Yes but no stoves are installed on a venting system like the one used in testing.

 

[BKVP]

Yes but no stoves are installed on a venting system like the one used in testing.

You are absolutely correct! From the post a few above.."Remember, in the method and in a lab we can control stack velocity. Our gases/emissions are dumped into a hood and do not exit in the manner a home installation occurs."

 

[bholler]

You are absolutely correct! From the post a few above.."Remember, in the method and in a lab we can control stack velocity. Our gases/emissions are dumped into a hood and do not exit in the manner a home installation occurs."

I know that. So if we are not installing on the vent system as tested why can't we manipulate the vent system within the guidelines of code and the vents listing to meet the draft requirements?

 

[begreen]

Not all manufacturers. We often here of stacks greater than 30' that we suggest they look at other options. When you have folks unwilling to run a liner "My clay liner has worked for over 40 years with my XXXX model"... Keep in mind that as of 2015, Owners & Operator Manuals have become Federally regulated documents. They are part of the certification process and must cover operational and installation specifications. So while some may wink wink nod nod, not here!

It's what's not being said in manuals that counts. Should stoves never be installed on a venting system where the draft exceeds the manual's specified upper limit, in spite of practical means to reduce draft?

 

[BKVP]

I can't obviously speak for others. However, we state desired draft measurements. We state minimum chimney lengths. In real world applications we know certain designs can address excessive draft better than others. The same holds true for inadequate draft as well. I'll review our manuals with this in mind.

 

[Crocks]

My 1997 Opel 2000 was a joke before I removed the "epa screw" in the draft control that kept the plate held open atleast 3/16" I now run a 28 guage shim ......


I call it a epa screw because it seems like a poor way to pass a emissions standard. Sure it will burn clean if you have no way to control the burn

 

[Crocks]

I should probably add I have about a 15' stove pipe. Straight shot to the cap. 8" diameter

 

[bholler]

I should probably add I have about a 15' stove pipe. Straight shot to the cap. 8" diameter

I have never heard of an opel 2000. What temps was it running at before you modified it?

 

[Crocks]

It is basically the same stove as a opel 2 from my understanding.
I never ran a guage on the top of stove before I modified my intake. I can say before the modification, when I closed the stove down(typically very early, trying to extend the burn) it would climb temp for about 1 hr then start declining. I would usually only get about 3-4 hrs of usable heat. I also almost never fully loaded the box because I was scared it was over firing . The stove would almost never have coals left in the morning and I felt like all my heat was blasting out the stack.

 

[sadpanda]

TL;DR

Getting additional draft is easy: add more pipe. Reducing draft is wrought with compromise and with current restrictions is technically impossible. The overdraft problem is virtually universal; even with a flat roof, any two story house will have a stack taller then mfg recommendations. This is illogical, poses eminent danger and should be rectified with extreme prudence

You can calculate all you want but those calculations don't mean a thing quite honestly. Like I said before there are way to many variables involved.

If you are maintaining the same flue gas temps with the heatreclaimer how would it reduce draft other than from the physical obstruction?

If you can't understand the potential dangers of an air intake elevated above the stove and the difference between that and a stove in the basement you have allot to learn.

As we are typing at each other with no verbal/facial cues, I will assume you are not being snarky and just scanning / reading quickly... So I will elaborate.

The calculations DO mean something, maybe not in your world but in theory and in practice for other professions. A heat reclaimer by definition reduces flue temp. I'm proposing a heat reclaimer with enhanced controls that does not allow excessive cooling.

A device like this is not currently made in the US as far as I know but could easily be diy... I'm thinking it would include a bypass damper and variable control fan. Once the fire was established, reclaimer bypass would be closed and flu gases would be redirected through tubes similar to boilers/current reclaimers. A continuously variable digitally controlled fan would use a thermocouple probe inserted near the chimney cap to ensure the flue exit temps do not drop below critical level. Depending on the thermal efficiency, it may be necessary to also track inlet temp or draft itself to ensure the total system draft is maintained through the entire burn cycle.

Regarding the potential pitfalls of an elevated air intake, please elaborate. I'm pretty sure I've got a firm grasp of all potential pitfalls, however I actually enjoy learning and encourage critiques so please, I'm all ears.

To be fair most expensive tires generally don't last past 20,000 miles, but that is due to being made from high performance compounds that just don't last long.

HA! Thats nothing! I'm happy if I get 20k miles on my brakes! Brake late, brake hard. I'm roughly 1:1 brake/tire changes right now.

Remember, in the method and in a lab we can control stack velocity. Our gases/emissions are dumped into a hood and do not exit in the manner a home installation occurs.

So EPA emissions and fuel economy testing is at least designed to mimic real life end user conditions.... It's GREAT to hear that the big brain regulators throw that logic out of the window when trying to regulate on of MANS OLDEST TECHNOLOGIES.

How many burning hours/cords per year are used in zones <4 vs zones 4 and above? At least 3/4 of the country is in climate zone 4 or higher, which I wager is where most wood burning occurs and where wood burning most dramatically effects air quality. EPA does not test emissions of vehicles at full throttle/max RPM, they test where the car spends 99% of its life: startup, idle, part throttle acceleration and freeway cruise. If 99% of the burning is done at 32F ambient and flues have virtually no maximum height but do have a hard minimum height, what cat brained bureaucrat decided testing in the current manner was a good idea? If I put on my tin foil hat, the only explanation that makes sense is the EPA is purposefully trying to put us in an impossible situation so we stop burning wood all together.

Well, they are not allowed to have any control mechanism to alter that single burn rate. The use of a damper in the flue can alter the burn rate.

The keys words are "as tested". No manufacturer to my knowledge tests with a flue damper....because it's not permitted in the dilution tunnel configuration. And if isn't used that way to test.....default to the first sentence.

You are VERY correct about the calculations/numbers not meaning much. The reason, variability. That will be my new buzz word for 2021!

OK.... I have a few thoughts on this.

1. Commercial boiler/power generation/gas residential appliances ALL have to cope with the same variables and have controls in place to regulate them; designed and integrated based on CALCULATIONS
2. if all responsibilities fall on the mfg for allowing installation configurations, there should be more guidance
3. if that responsibility is shoved down to sweeps/installers, where is their training/guidelines/certifications? Why are they not held to the same standards that all other contractors are held to ie calculations, not guess and check
4. if calculations are useless, how did you @BKVP arrive at thechimney height recommendations for various elevations? SWAG? Seems you are at least doing some basic air density adjustments
5. draft, stack velocity, thermo dynamics are not PFM... The fundamentals are very basic, and we have this new thing called Computational Fluid Dynamics. If we can correctly model/predict/design the thermal transfer of a heat sink, the airflow around a body in motion, the way atomized fuel droplets bounce off of a piston or the thermal losses through a complex building envelop comprised of many varying materials and assemblies... we can CERTAINLY generate some common flue models and establish some standards.

I can't obviously speak for others. However, we state desired draft measurements. We state minimum chimney lengths. In real world applications we know certain designs can address excessive draft better than others. The same holds true for inadequate draft as well. I'll review our manuals with this in mind.

By the way, stick a coupon good for a $100 bill in 50 random manuals. Insert those manuals along with 950 others into stoves coming off the line. Put an expiration date of 12/31/2020 on them. You won't wind up paying more than $1500. Sad.....but as pointed out earlier in another post and many times before.....this family is unique amongst wood burners.

If mfgs put $100 bills in manuals, I would be a very wealthy man! Speaking of manuals

• My old PI1010A manual does in fact state 0.05" WC operating on high and 0.06" as unsafe... That's a very, very tight band.

- - - - HOWEVER - - - -

• NONE of the current manuals that I checked have any draft specification (I looked at 5, I'll keep my eye on the mailbox for that $500 check ), though .'...maintain draft to manufactured specifications' is sited in combustor troubleshooting and sections 'DRAFTS' and 'CHIMNEY DRAFTS' sections are referenced but are MIA. The only exception I found was PI29 manual where the 'Combustor Troubleshooting' does at least mention 'do not exceed 0.06"WC'

 

[SpaceBus]

HA! Thats nothing! I'm happy if I get 20k miles on my brakes! Brake late, brake hard. I'm roughly 1:1 brake/tire changes right now.

Are you daily driving on your race brakes? Even with super aggressive autocross compounds I get pretty long life out of my brakes, usually outlasting two sets of 200tw tires. I'm driving a giant truck now, so no more race car stuff for a while.

 

[sadpanda]

Are you daily driving on your race brakes? Even with super aggressive autocross compounds I get pretty long life out of my brakes, usually outlasting two sets of 200tw tires. I'm driving a giant truck now, so no more race car stuff for a while.

I did for a summer because I liked them so much and the dust trashed my wheels I'm back on OE brembos for the winter. Despite being in ohio, I live in the sticks and happen to have a few good roads and a very early commute so I take full advantage every day. My current daily should be getting 31mpg+ My total average is 17.

 

[BKVP]

The point I was trying to make is not all buyers of wood stoves read the manuals and of those that do most discard the technical suggestions.

Sit at my desk for a day and you'll see it!

 

[john26]

I like sadpandas thought of controlling draft but I don't think a heat reclaimer would be practical even though it may help some. I think a more logically solution would be some sort of permeant installed manometer built into the chimney system then a manual adjustment draft limiting damper built in the stove top. Yes it would rely on the user to be be educated on its use and use it properly, but every stove user should do that anyway. Most people who are not using their stoves in properly are running out of date smoke dragons are just bought a house with an existing install many wind up here any way to be educated. A thermocouple mounted in the chimney to open and close an automated damper similar to a barometric may work but would also need to take a chimney draft measurement into account. At that point it would only regulate when the chimney is above 250F. A built in draft regulator on the stove top would be the most practical and aesthetically pleasing but in all reality its would be nothing more than a key damper.

 

[begreen]

Installers should be required to read the manuals. The installation documentation should include maximum flue height as well as the minimums when the max is known to be an issue for the stove or insert. We get several cases of too strong draft a week where the documentation is zero help or passes the buck by saying something like consult your dealer or a chimney sweep.

 

[begreen]

A basic heat reclaimer can reduce draft, at the expense of dramatically increasing creosote accumulation. They are also butt ugly and noisy. The reclaimer that sadpanda describes is not too far from what MF Fire was testing, but with the upper thermocouple in the room IIRC. It's a costly setup.

 

[Nate R]

Using calculations at hand ( I made an excel doc for everyone to scrutinize/play with : FlueCalc ) , the only way to achieve this magic number is with 70F ambient temp and an average flue temp of 230F resulting in a calculated 140 CFM. With that low of an average temp, this seems to match the EPA's very 'lossy' worst case scenario installation, aka class A pipe outside the structure. If you drop ambient temp down to freezing you get 0.06" @ 162 CFM and if you go to 0F you get 0.08" @ 181 CFM. Furthermore if you reset ambient back to 70 but bump the average temp to what I was observing last year (400F, average of flue temp vs cap temp over duration of entire burn cycle) you get 0.083" and 202 CFM.

The CFM #s here don't make sense in relation to wood stoves. From my glance at your fluecalc sheet, I suspect the stack effect CFM calcs would apply in an open room, but don't account for intake air restriction. So, maybe these CFM numbers are accurate for an open fireplace, but I don't think they apply to a modern wood stove.

Example: I entered these numbers: 6 inch flue, 70 deg ambient temp, 15 ft chimney, and 500F flue temp. Your calculator says that should result in 230 CFM of flow.

OK, let's check this another way. To get 230 CFM of air to go from 70 degrees to 500, you'd need nearly 107,000 BTU an hour JUST to heat the air going up the flue...not even looking at the btus going into the room! Modern wood stoves aren't delivering more heat up the flue than they are to the room. I don't think we're burning 12+ lbs of wood an hour JUST to heat the flue air.
(see (broken link removed) )

EPA test reports for wood stoves sometimes contain flue CFM measurements. They sometimes also contain a drawing/sketch/description of the flue setup used. Jotul has theirs online here: https://www.jotul.com/epa-certifications
The 2001 F100 test report showed only 5-11 CFM average stack flows during their test burns, into a 14 foot chimney. (Looks like they measured it as well as calculated it from a mass-balance standpoint).

My point is, the calcuations don't seem to make sense in this case, and we can sometimes see what tested drafts and flue flows are if you look at the EPA Cert Reports.

 

[Nate R]

I should add that I get the OP's points, and I think there's definitely some valid ones there in how things are looked at in this realm. Not knocking that, but I'm maybe at a different....order of magnitude than the OP in how I think about this.

 

[bholler]

The calculations DO mean something, maybe not in your world but in theory and in practice for other professions.

I am not bring snarky at all. I am simply telling you that your calculations don't take into account many many variables we deal with every day in the field that can drastically effect the actual measured draft. I would love it if there was a simple formula that could tell us accurately what the draft in a given chimney will be. But there simply is not.

A heat reclaimer by definition reduces flue temp. I'm proposing a heat reclaimer with enhanced controls that does not allow excessive cooling.

I know what you are saying. And if an appliances output temp was high enough it may work. But most modern stoves do not have high enough output temps to be able to pull extra heat off of the stack and stay above the condensation point. You are also talking about adding a massive amount of electronics to woodstoves when a simple manually controlled key damper almost always works perfectly fine.

Regarding the potential pitfalls of an elevated air intake, please elaborate. I'm pretty sure I've got a firm grasp of all potential pitfalls, however I actually enjoy learning and encourage critiques so please, I'm all ears.

An elevated air intake can and has acted as a second chimney sucking flue gasses out of the stove through the intake pipe causing a fire.

This is no longer allowed because of problems that arose which is how many codes come about.

 

[Highbeam]

Heat reclaimers above a modern wood burner work very well in the wood furnace world. They call them heat exchangers but the exhaust from the firebox is routed through a back and forth series of small pipes within a blower box prior to leaving the appliance. Often, these things run output flue temperatures below 200 as measured with a flue probe! Minimal electronics prevent overcooling the exhaust, rather, they measure plenum temperatures and vary the blower speed.

Above a woodstove designed to strip as much heat as possible from the flue gasses to be efficient, I would not add a heat reclaimer.