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

[sadpanda]

So is there no way to check your draft prior to your stove install? I have the installer coming tomorrow for a quote, and it'd be nice to measure a draft prior to a full install. I guess you just have to go off the installer's experience and assumptions based on your chimney size, location, geography, etc? - and then hold off on a formal draft measurement until it's installed and running (at which point you already paid for everything)

Yes draft can be estimated given all of the fixed variables that are out of your control:

Flue size is fixed by a)what fits down your masonry if doing a re-line which can impact the main determinant: b) the collar size of the appliance you are seeking to install.

Flue height has a minimum set by building/fire code.

Flue average temp is something I think could be calculated if the industry decided to help on this but annecdotally my 24 ft flex liner with wrap going through exterior masonry chimney was loosing around 200F from collar to cap. This would be drastically different for an exterior exposed Class A installation.

Outside ambient temp, again per my recommendation the building code uses this for your heating/cooling calcs so it readily available.

Chimney Sizing

Calculate chimney draft and required chimney area - online calculator.

www.engineeringtoolbox.com

 

[Bad LP]

At the end of the day the manufacturers call the shots on what is and is not allowed.

 

[bholler]

Yes draft can be estimated given all of the fixed variables that are out of your control:

Flue size is fixed by a)what fits down your masonry if doing a re-line which can impact the main determinant: b) the collar size of the appliance you are seeking to install.

Flue height has a minimum set by building/fire code.

Flue average temp is something I think could be calculated if the industry decided to help on this but annecdotally my 24 ft flex liner with wrap going through exterior masonry chimney was loosing around 200F from collar to cap. This would be drastically different for an exterior exposed Class A installation.

Outside ambient temp, again per my recommendation the building code uses this for your heating/cooling calcs so it readily available.

Chimney Sizing

Calculate chimney draft and required chimney area - online calculator.

www.engineeringtoolbox.com

There are way to many variables to get anywhere near an accurate number. But it is a safe bet that if you get much over 20' straight up off the stove your draft will be to strong. More height if going through a wall.

Flue height does not have a minimum according to fire code. It has to be a certain distance above the surrounding structure. And stove manufacturers specify a minimum height.

 

[sadpanda]

You are a little confused about what is allowed and what isn't and who determines that.

The epa only sets emissions standards. They have absolutely no input at all in the design installation operation etc of stoves.

Key dampers are allowed unless the manufacturer says you can't use one. No agency says you can't.

Flue size. Nfpa allows downsizing or upsizing by 1" unless the manufacturer says otherwise.

Flue restrictor. Same as the others a manufacturer can allow it.

Barometric dampers. Again same as above but I honestly still believe they are a horrible solution to draft control on a wood stove.

Modify the stove yes everyone has to say it isn't allowed because making untested modifications to a stove could be extremely dangerous. But many people have successfully restricted the intake of their stove if they have excessive draft.

Now all that being said I do agree there is a problem that there is no set way to compensate for excessive draft. I really wish there was a way as an installer that I could preset the intake for the draft in that particular installation. Especially for inserts. Freestanding stoves are pretty easy to address with a key damper.

Now we also have to look back before regulations. All of those problems you listed absolutely existed before regulations came into the equation. And honestly for the vast majority people if they install correctly and use good fuel modern stoves work very well.

EPA sets emissions standards.... The stoves are #1 designed to pass this test. Otherwise they are not allowed to be sold. Any other considerations are secondary.

From what I've seen, no current EPA stove mfg is publically encouraging the use of Key dampers for fear of EPA reprecussions (that would basically be the folksy version of VW Diesel-Gate).


What section of NFPA 211 allows for up size or down size?

9.2.2.2.1: reduced clearance connectors permitted if they are in accordance with mfg
9.4.2: effective area of connector shall not be less than the area of the appliance flue collar

I did not look for size reduction allowed on B-vent but I remember seeing it in Selkirk installation manual... perhaps that falls under 'engineered ventilation' because, oh, I dunno, someone actually had a table/procedure to reference and could do maths to verify it would work

 

[sadpanda]

There are way to many variables to get anywhere near an accurate number. But it is a safe bet that if you get much over 20' straight up off the stove your draft will be to strong. More height if going through a wall.

Flue height does not have a minimum according to fire code. It has to be a certain distance above the surrounding structure. And stove manufacturers specify a minimum height.

Erm... "It has to be a certain distance above the surrounding structure." aka there is a minimum set by fire/building code.

If I have a 20ft tall house and too much draft, shortening my flue is not an option

 

[sadpanda]

Draft needs to be measured on the stove side of the damper. Temp on the chimney side

And you are back to the issue at hand. Draft during shoulder season for me(ambient temp 50F) vs dead winter on the coldest night (12F) is dramatically different. Draft with the air controls open on a fresh load are dramatically different than they are at high cruise (aka riding the hole for BK owners) vs coaling end of the load. ALL of this is WAY different than the FL warm day worst case scenario the EPA tests with and the stoves are designed for.

So when is this magical 0.05" WC suppose to happen and how are you suppose to maintain it without some sort of barometric control?

 

[sadpanda]

There are way to many variables to get anywhere near an accurate number. But it is a safe bet that if you get much over 20' straight up off the stove your draft will be to strong. More height if going through a wall.

I logged every fire for two years using a 4ch thermocouple data logger because no one believed the readings I was getting on the draft gauge, myself included. After running the numbers, the formulas work. If someone took the time to generate data for the resulting R value for various chimney configurations it would be a piece of cake. This still would only put you in the average though, without barometric or some other CFM controls, we are just playing with hand grenades .

 

[bholler]

From what I've seen, no current EPA stove mfg is publically encouraging the use of Key dampers for fear of EPA reprecussions (that would basically be the folksy version of VW Diesel-Gate).

Nothing to do with epa standards at all. The epa has nothing to do with it after it passes emission testing.

What section of NFPA 211 allows for up size or down size?

I don't remember off hand and after a 10 he day working on chimneys for paying customers I am not looking it up now. I will another time.

Erm... "It has to be a certain distance above the surrounding structure." aka there is a minimum set by fire/building code.

That height is set by your house. But yes I guess there is a minimum chimney height required. That would be the thickness of your roof plus 3' not enough to cause draft problems.

And you are back to the issue at hand. Draft during shoulder season for me(ambient temp 50F) vs dead winter on the coldest night (12F) is dramatically different. Draft with the air controls open on a fresh load are dramatically different than they are at high cruise (aka riding the hole for BK owners) vs coaling end of the load. ALL of this is WAY different than the FL warm day worst case scenario the EPA tests with and the stoves are designed for.

So when is this magical 0.05" WC suppose to happen and how are you suppose to maintain it without some sort of barometric control?

Like I said check with the manufacturer. What I gave were very general rules.

I logged every fire for two years using a 4ch thermocouple data logger because no one believed the readings I was getting on the draft gauge, myself included. After running the numbers, the formulas work. If someone took the time to generate data for the resulting R value for various chimney configurations it would be a piece of cake. This still would only put you in the average though, without barometric or some other CFM controls, we are just playing with hand grenades .

You are forgetting all of the variables of house pressures, effects from topography trees etc.

 

[ejsechler]

Was this a professional install or DIY?

Have you started a thread on this topic? If not, please do. In it let us know the specifics of the install including the height of the entire flue system.

I have a 25ft chimney. DIY install, wood is 15 to 20 percent 6" to 8" splits have been sitting for 2 years. I start backing down the stove once the probe temp reads 375 when it hits 450 I am closing the primary air completely. Yet the stove still goes up to 1300 degrees. Probe is 20" from stove top. I have a excessive draft i did some experimenting. I covered the unregulated air hole drilled through the primary air and ramped my stove up on purpose and then completely shut her down and my stove stayed at 900 and that is with the hole covered completely. So I need a damper or just run it with a modified primary air damper. But even with plugging it complelty I still feel like I could run a damper on top of it.

 

[bholler]

I have a 25ft chimney. DIY install, wood is 15 to 20 percent 6" to 8" splits have been sitting for 2 years. I start backing down the stove once the probe temp reads 375 when it hits 450 I am closing the primary air completely. Yet the stove still goes up to 1300 degrees. Probe is 20" from stove top. I have a excessive draft i did some experimenting. I covered the unregulated air hole drilled through the primary air and ramped my stove up on purpose and then completely shut her down and my stove stayed at 900 and that is with the hole covered completely. So I need a damper or just run it with a modified primary air damper. But even with plugging it complelty I still feel like I could run a damper on top of it.

I really prefer to limit the draft when possible over limiting the intake. There are times both are nessecary though.

 

[ejsechler]

I really prefer to limit the draft when possible over limiting the intake. There are times both are nessecary though.

I get it but as of now I am not able to make it to my local shop to pick one up. This is just temporary until I get up there this weekend. I honestly don't get why they put a hole in the primary air anyways. The only thing I can come up with is it is for epa bullshit so you can't smudge the fire out and it burns cleaner to keep the particulates down. Well I say screw the EPA.

 

[bholler]

I get it but as of now I am not able to make it to my local shop to pick one up. This is just temporary until I get up there this weekend. I honestly don't get why they put a hole in the primary air anyways. The only thing I can come up with is it is for epa bullshit so you can't smudge the fire out and it burns cleaner to keep the particulates down. Well I say screw the EPA.

Epa regulations on woodstove have given us far better stoves to use than we would have otherwise. Yes I will readily admit there are some problems. But generally if installed properly those problems can be overcome without much issue. You may find partly obstructing that hole in combination with a damper may work best.

 

[kennyp2339]

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.

 

[Woody5506]

After reading through this thread I think I might be a bit more grateful now for my 12' stack on my T5 which I have wondered if it was under drafting.

 

[SpaceBus]

To prevent excessive draft you need to close the intake with rising flue temps. I start closing my Morso down when the flue reads 175 surface temp, maybe even lower if the fire has taken off. You have to ride that line between killing the fire and keeping it going.

 

[Nigel459]

To prevent excessive draft you need to close the intake with rising flue temps. I start closing my Morso down when the flue reads 175 surface temp, maybe even lower if the fire has taken off. You have to ride that line between killing the fire and keeping it going.

This is the ideal, when one can "ride the line" as you describe. Many modern stoves, usually with long >20' flues in cold climates, simply can't ride that line no matter how early and how much you turn them down. They just go. Nowhere close to stated burn times or efficiencies (which does seem to me to be on the mfg who is advertising said attributes) even with proper fuel and operation. Thus the decades-old discussion about what to do about it.

It does seem curious to me that there hasn't been any standardization or requirement to measure draft, especially when some excessive draft conditions can be downright dangerous, as reported on these forums many times...

 

[SpaceBus]

This is the ideal, when one can "ride the line" as you describe. Many modern stoves, usually with long >20' flues in cold climates, simply can't ride that line no matter how early and how much you turn them down. They just go. Nowhere close to stated burn times or efficiencies (which does seem to me to be on the mfg who is advertising said attributes) even with proper fuel and operation. Thus the decades-old discussion about what to do about it.

It does seem curious to me that there hasn't been any standardization or requirement to measure draft, especially when some excessive draft conditions can be downright dangerous, as reported on these forums many times...

I also have an oversized chimney, lots of 90's in the flue, and single wall which probably helps me tame the draft. When I update the square liner with insulated 6" I might change my opinion and get a key damper. My cookstove has few bends and sometimes I have to control the output with fuel load rather than control the draft. Since the cooker doesn't need to have long burn times this doesn't really affect anything, but on the primary heater it could.

 

[sadpanda]

From the barometric damper thread

As far as measuring draft you would have to check with the manufacturer but it can be pretty much anywhere in the stove or connector pipe. And it is typically measured at high operating temp with full air.

My draft during these conditions easily exceeds 2.0" and turns my stove into a runaway forge, sucking flames well into the stove pipe.

The BK manual states minimum flue height of 15ft. Lets assume flue pipe matches appliance collar as per normal recommendations. 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.

Draft varies significantly with ambient temperature and wildly depending on stove operating mode ( when my BK reaches set point via thermostat and is 'riding the hole' my draft goes up 0.04"+). Back to 'ideal' scenario (70F/230F), adding 10ft of chimney also gets us up to 0.083" but only 181 CFM.

Assuming my maths are correct (anyone please verify), CFM rather than draft is what we should be concerned with. A key damper does reduce CFM via restriction however, it seems the most direct way to control CFM is via average flue temp.

Enter the heat reclaimer... If you had heat reclaimer, draft controlled and thermostatically controlled via thermocouple at the chimney cap (not allowing cap temp to fall below 250F), that would satisfy your 'no diluted exhaust' argument against barometric controls yes?

Back to barometric dampers, so what if a damper is admitting cold air into the exhaust? If the cap temp never falls below 250F it should not matter.

There is of course another option; snorkeling the stove inlet: Air tight OAK with a vertical extension on the pipe, effectively shortening the stack. The BK manual says 'do not route this any where' however in reality this is no different than having a stove in a basement IMHO.

 

[bholler]

From the barometric damper thread



My draft during these conditions easily exceeds 2.0" and turns my stove into a runaway forge, sucking flames well into the stove pipe.

The BK manual states minimum flue height of 15ft. Lets assume flue pipe matches appliance collar as per normal recommendations. 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.

Draft varies significantly with ambient temperature and wildly depending on stove operating mode ( when my BK reaches set point via thermostat and is 'riding the hole' my draft goes up 0.04"+). Back to 'ideal' scenario (70F/230F), adding 10ft of chimney also gets us up to 0.083" but only 181 CFM.

Assuming my maths are correct (anyone please verify), CFM rather than draft is what we should be concerned with. A key damper does reduce CFM via restriction however, it seems the most direct way to control CFM is via average flue temp.

Enter the heat reclaimer... If you had heat reclaimer, draft controlled and thermostatically controlled via thermocouple at the chimney cap (not allowing cap temp to fall below 250F), that would satisfy your 'no diluted exhaust' argument against barometric controls yes?

Back to barometric dampers, so what if a damper is admitting cold air into the exhaust? If the cap temp never falls below 250F it should not matter.

There is of course another option; snorkeling the stove inlet: Air tight OAK with a vertical extension on the pipe, effectively shortening the stack. The BK manual says 'do not route this any where' however in reality this is no different than having a stove in a basement IMHO.

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.

 

[BKVP]

What do the epa’s ever tightening regulations have to do with my catalyst only lasting 2 seasons?They’ve only been rated to last 12,000 hours for decades.

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!

 

[BKVP]

You are a little confused about what is allowed and what isn't and who determines that.

The epa only sets emissions standards. They have absolutely no input at all in the design installation operation etc of stoves.

Key dampers are allowed unless the manufacturer says you can't use one. No agency says you can't.

Flue size. Nfpa allows downsizing or upsizing by 1" unless the manufacturer says otherwise.

Flue restrictor. Same as the others a manufacturer can allow it.

Barometric dampers. Again same as above but I honestly still believe they are a horrible solution to draft control on a wood stove.

Modify the stove yes everyone has to say it isn't allowed because making untested modifications to a stove could be extremely dangerous. But many people have successfully restricted the intake of their stove if they have excessive draft.

Now all that being said I do agree there is a problem that there is no set way to compensate for excessive draft. I really wish there was a way as an installer that I could preset the intake for the draft in that particular installation. Especially for inserts. Freestanding stoves are pretty easy to address with a key damper.

Now we also have to look back before regulations. All of those problems you listed absolutely existed before regulations came into the equation. And honestly for the vast majority people if they install correctly and use good fuel modern stoves work very well.

Not exactly accurate. EPA's NSPS specifically makes certain acts illegal. Installations that can alter low burn rates are illegal. Installing a solid fuel heater inconsistent with the Owners & Operator manual is also a Federal violation. They do in fact regulate particulates, but there is much, much more they regulate. If you need more let me know...the rule sits on my desk.

 

[BKVP]

And, it really should be noted the EPA can delegate the authority to other agencies. That did not exist prior to 2015. Lest your neighbor complains about excessive smoke and you have a local authority schedule a visit to review your installation.

 

[bholler]

Not exactly accurate. EPA's NSPS specifically makes certain acts illegal. Installations that can alter low burn rates are illegal. Installing a solid fuel heater inconsistent with the Owners & Operator manual is also a Federal violation. They do in fact regulate particulates, but there is much, much more they regulate. If you need more let me know...the rule sits on my desk.

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.

 

[begreen]

After reading through this thread I think I might be a bit more grateful now for my 12' stack on my T5 which I have wondered if it was under drafting.

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.

 

[Highbeam]

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!

If the Toyo tires are bald and worthless at 20,000 miles every dang time then you might get an idea why they would suggest that. If nobody made a longer lasting tire (cat) you can budget and plan for new tires(cats) at 20,000 mile intervals. Wouldn't it be exceedingly wrong of TOYO to rate/warranty their tire in terms of "years"? Some users drive 100,000 miles per year!

Not certain online retailers, the actual manufacturers rate these cats for 12,000 hours. That and repeated forum members sharing real life experience. I'm willing to go along with your usual argument that we use our stoves more than the general public though, 12000 hours might take 20 years for an average wood stove user.

Please please invent a longer lasting catalyst. These things really work well until they wear out.

On Edit: Yikes, Applied Ceramics writes that we can only expect to squeeze 10,000 hours out of a catalyst and should replace at 6 year intervals. http://firecatcombustors.blogspot.com/