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

[Hoytman]

... Just give us the formulas / reference tables like everything else. The formula for calculating theoretical draft is simple enough. Adjust for local average winter ambient temperature, type of flue pipe and installation method and BOOM we are in the ball park. Two k-type thermocouples, a data logger and a manometer can all can be had for peanuts on Amazon. Heck even wide band O2 sensors are standard fare for the average automotive enthusiast if we want to go full EU emissions geek. Do the calcs, add in a couple of monitored test burns for fine tuning/user training/validation and voila! We have a fully commissioned, safe, functional installation that keeps the EPA dweebs happy.


Why is this so hard?

/rantff

Can you provide the formulas you mentioned? I need them to calculate theoretical numbers... because I have the manometer and getting ready to buy thermo couples and maybe even O2 censors to get my geek on.
Would have already had this but we had a date with corona for a minor set-back.

Now I’m going to read the rest of the thread.

 

[Hoytman]

A 4" pipe on a 6" stove will not have enough volume on startup and will smoke back into the house. Draft measurement is only one part of the equation. You also have to have the correct volume.

Why should key dampers be avoided??? If you are using it to bring draft into spec you would not have smoke spillage at all when you open the door.

Also the "magic EPA honeycomb thing" only works.
1 if there is one which many stoves don't have one.
2 if there is enough temp to keep that cat active.

I just wonder how many guys that have the old Fisher stoves with 8” breech reduced to 6” have encountered smoke into the room on start-up? Coaly is one that has discussed this many times...reducing the pipe and liner size on these stoves for increased draft.

 

[bholler]

I just wonder how many guys that have the old Fisher stoves with 8” breech reduced to 6” have encountered smoke into the room on start-up? Coaly is one that has discussed this many times...reducing the pipe and liner size on these stoves for increased draft.

I actually think they work best on 7". I have had customers who has issues running on 6" but others who it worked fine for.

One key thing is a larger flue does not mean more draft. The draft is the same but volume and velocity change

 

[Hoytman]

Old big green machines are brining huge bucks at auction right now because of this very reason. Stupid expensive service calls for what is quite simply... Goofed up eeeeelectronic gadgets/gizmo's that are causing crazy down time in a mother nature limited time frame. Noooo good.

goofed up? Nope!! More like designed in.

 

[Hoytman]

These automated dampers at the top of the chimney that keeps getting mentioned...has already been done on the other end of the system...it’s called Hitzer, D.S. Machine, Blaze King, Vermont Castings, and others...in the form of bi-metallic thermostats...and in at least two cases with no longer made Quadra-fire computer automated stoves controlling incoming primary and secondary air. I forget the particular model.

On the subject of barometric dampers it has been explained to me to view them as pressure sensitive two-way valves on the chimney side of the system that responds to push (down draft situations) and pull ( high wind situations) in order to maintain a given draft range or pressure within the system. Hard enough to think about their use in a coal or gas situation let alone worrying about wood burning and cooling flue gases forming creosote. Not taking a side on whether they should be used for wood, but you muddy the water, so-to-speak, when you start worrying about room air compromising flue temps versus the BD doing it’s job of maintaining proper chimney pressures and therefore proper draft range. That’s how it was explained to me and it seems much easier to think about it and understand it’s proper function in those terms...at least for me.

 

[bholler]

These automated dampers at the top of the chimney that keeps getting mentioned...has already been done on the other end of the system...it’s called Hitzer, D.S. Machine, Blaze King, Vermont Castings, and others...in the form of bi-metallic thermostats...and in at least two cases with no longer made Quadra-fire computer automated stoves controlling incoming primary and secondary air. I forget the particular model.

On the subject of barometric dampers it has been explained to me to view them as pressure sensitive two-way valves on the chimney side of the system that responds to push (down draft situations) and pull ( high wind situations) in order to maintain a given draft range or pressure within the system. Hard enough to think about their use in a coal or gas situation let alone worrying about wood burning and cooling flue gases forming creosote. Not taking a side on whether they should be used for wood, but you muddy the water, so-to-speak, when you start worrying about room air compromising flue temps versus the BD doing it’s job of maintaining proper chimney pressures and therefore proper draft range. That’s how it was explained to me and it seems much easier to think about it and understand it’s proper function in those terms...at least for me.

Close but it is only a one way valve. It it set to only let a certain ammout of vacuum to the stove. If the chimney has to much suction it opens reducing the suction on the stove. It doesn't change the actual draft in the chimney just the draft that reaches the stove. It stays closed (but leaks) when draft is low

 

[sadpanda]

Can you provide the formulas you mentioned? I need them to calculate theoretical numbers... because I have the manometer and getting ready to buy thermo couples and maybe even O2 censors to get my geek on.
Would have already had this but we had a date with corona for a minor set-back.

Now I’m going to read the rest of the thread.

I linked all of formulas and spreadsheets in previous posts

Datalogger I've been using for temps: Amazon product ASIN B01HD4WMS8

 

[sadpanda]

One key thing is a larger flue does not mean more draft. The draft is the same but volume and velocity change

Yes... And THAT is why its so DUMB to only focus on draft and to only be given draft recommendations... We are having VOLUME issues.

I believe the solution is very simple. MFGs just need to publish CFM requirements instead of the sporadic and vague 'draft recommendation'. Let the sweeps/end users break any/all EPA laws required to achieve safe/optimum operation.

 

[sadpanda]

I have experimented with room air for the BD, vs air from direct connect OAK...the damper opens less, to do the same job, when using the OAK.

Was the stove on OAK or just the BD?

Draft is a measure of differential pressure. Barometric damper is a differential valve...

Assuming your stove is not hooked to outside air, the stove slightly depressurizes the room and make up air comes from outside air infiltrating your home via windows/leaks.

Having the BD taking air from the same room as the appliance means both are fighting for this same makeup air. Remember, chimney draft works because flue temp/height relative to AMBIENT or outside air. Your house functions as virtual damper...

However, if stove AND the BD are getting outside air, neither is fighting the resistance of cracks/seals etc. In this situation, YES temperature plays a part just not a huge one. Playing with my excel sheet, decreasing average flue temp by 80F delivers a 0.01" WC and 22 CFM reduction (6in pipe, 15ft, 32F ambient, 500>420F). Assuming avg flue temp is kept above condensation point, the only possible point of creosote formation should be right at the BD inlet.

 

[bholler]

Was the stove on OAK or just the BD?

Draft is a measure of differential pressure. Barometric damper is a differential valve...

Assuming your stove is not hooked to outside air, the stove slightly depressurizes the room and make up air comes from outside air infiltrating your home via windows/leaks.

Having the BD taking air from the same room as the appliance means both are fighting for this same makeup air. Remember, chimney draft works because flue temp/height relative to AMBIENT or outside air. Your house functions as virtual damper...

However, if stove AND the BD are getting outside air, neither is fighting the resistance of cracks/seals etc. In this situation, YES temperature plays a part just not a huge one. Playing with my excel sheet, decreasing average flue temp by 80F delivers a 0.01" WC and 22 CFM reduction (6in pipe, 15ft, 32F ambient, 500>420F). Assuming avg flue temp is kept above condensation point, the only possible point of creosote formation should be right at the BD inlet.

And how do you propose flue gas temps are kept above the condensation point when dumping unknown ammounts of outside air into the stack just past the stove?

 

[AndrewU]

Hope you don’t mind a brief interruption of the technical discussion.

Pretty sure I should be fine, but can you all comment on my likely draft before I do my first test fire. Stove is a BK Ashford 30.2, perfectly straight run of 18’ collar to cap. Elevation about 150-180’ ASL. 2 story house, chimney is more than 10’ horizontally from the peak, so with an 8/12 pitch chimney extends about 9-9.5’ from the roof (8’8” code minimum). Duravent brand double wall chimney with a telescoping double wall black pipe connecting the stove to the class A chimney (elevated hearth so only 4’ from collar to ceiling box).

ETA: I have an OAK for it too.

 

[Highbeam]

Hope you don’t mind a brief interruption of the technical discussion.

Pretty sure I should be fine, but can you all comment on my likely draft before I do my first test fire. Stove is a BK Ashford 30.2, perfectly straight run of 18’ collar to cap. Elevation about 150-180’ ASL. 2 story house, chimney is more than 10’ horizontally from the peak, so with an 8/12 pitch chimney extends about 9-9.5’ from the roof (8’8” code minimum). Duravent brand double wall chimney with a telescoping double wall black pipe connecting the stove to the class A chimney (elevated hearth so only 4’ from collar to ceiling box).

ETA: I have an OAK for it too.

Your chimney sounds excellent. Hopefully you have a roof brace since the chimney sticks up so high. 15’ minimum height and you’re at 18’. Should be great.

 

[AndrewU]

Your chimney sounds excellent. Hopefully you have a roof brace since the chimney sticks up so high. 15’ minimum height and you’re at 18’. Should be great.

Yes, roof braces were used. We did hire a fireplace guy to do the roof work. I can do a lot myself, but I don’t do roof work. Especially with an 8/12 pitch.

 

[stoveliker]

Yes... And THAT is why its so DUMB to only focus on draft and to only be given draft recommendations... We are having VOLUME issues.

I believe the solution is very simple. MFGs just need to publish CFM requirements instead of the sporadic and vague 'draft recommendation'. Let the sweeps/end users break any/all EPA laws required to achieve safe/optimum operation.

Draft is a measure of differential pressure. Barometric damper is a differential valve...

There is some truth in that draft is not the right terminology. But draft is also not differential pressure.

Draft in Chimneys

www.scientificamerican.com

copied from a pdf, so some spelling issues, but readable. From 1869 ...!

What matters is the total airflow through the system, as you recognize. However, flow is created by a driving force and a resistance in the system. Those are the knobs one can tune.

Given that the impedance in a (proper) chimney is negligible when compared to the impedance of the stove, what matters is the pressure difference in the chimney (the driving force), and the impedance (resistance) of the stove. The first is the engine for the system operating, and the latter is the bottleneck limiting the flow.

These two aspects determine the flow. (And yes, the temperature of the flue gases affects the pressure difference created in the chimney.)

Focusing on flow may therefore be correct, but it's a *derived* quantity. One cannot "dial in" a flow. One can dial in a chimney length. Flow is the volume of gas at a certain pressure and temperature which goes through a cross sectional area per second ... see how complicated that gets if mfg's would tell you "x cubic foot per minute at 300 F"? How'd the average customer do that...).

As the impedance of the stove is not controllable (beyond the tuning of the air inlet - and that has been controlled by the mfg by limiting your options to (almost) closed and "xx square inch open"), what remains is the "engine" that gets the system going: i.e. the pressure difference.

For a given stove (and when reading a manual with mfg instructions, the stove is "given", i.e. won't change), a certain range of pressure difference created by the chimney will allow the stove to operate. As that range is to a large extent determined by the chimney length, with outside temps, local geography, wind conditions, etc, being *perturbations* (only, even if sometimes substantial) on this chimney length, AND with the length being easily prescribed while the perturbations cannot be dictated, ... as all that, the manufacturers do focus on chimney length. To make the length a decent proxy for the driving force they need, they tell you not to put 90 degree elbows, and a horizontal length of more than xx ft.

Do the chimney (length, geometry) right, and yes, the system will work.

Finally, to have manufacturers prescribe lengths that in fact will make customers happy despite the (sometimes substantial) perturbations of uncontrollable local circumstances, manufacturers will add a safety margin into their calculations.

So, forgive my lecturing - it's a personal flaw - but I think this discussion so far somewhat misses the point (driving force and resistance rather than derived quantities), and I hope the above explains the "why" of chimney length prescriptions - it is simply the most deterministic knob a mfg can dictate to make sure things work.

 

[Isaac Carlson]

A lot of the things you mention are because of user error. You need to learn about anything you are going to use BEFORE using it. So many people install a wood stove and try to burn any wood they can find. They don't know about it works or what maintenance to do. And some of them just don't care. The rest just don't know and are oblivious to the fact that everything in the world needs maintenance.

There are draft tables and chimney size/area charts. It is all available Online or from some stove installers.


this one is metric, but you can convert it.

 

[john26]

I was wondering if anyone has a picture or used a draft limiter form Pacific Energy? The more I read about the EBT, my understanding is that the stove has a small allowable amount of air flow on the secondary's normally. When the draft increases it sucks open the small baffle allowing extra air in the secondary manifold like a boost mode then closes down again as the fire decreases slowing draft back down. Is my under standing of this correct?

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[MR. GLO]

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



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.



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.


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.


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.

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'

View attachment 268890View attachment 268891

jotul lists draft.

 

[bholler]

jotul lists draft.

Every manufacturer will provide a draft spec if asked. Most also have technical manuals that are much more detailed

 

[DBoon]

This might have already been answered in this post, but practically speaking can anyone tell me where to find information on:

1. Realistic draft reductions due to horizontal runs or elbows?
2. Realistic draft reductions due to size of chimney pipe (friction loss of smaller pipe versus larger pipe)?
3. Realistic draft reductions due to chimney caps?
4. Realistic draft reductions possible with a pipe damper?

I know that I am going to have a problem with a 27' chimney on a new install, but it would be nice to be able to calculate the extent of the problem I'll have relevant to the stove I will install.

 

[bholler]

This might have already been answered in this post, but practically speaking can anyone tell me where to find information on:

1. Realistic draft reductions due to horizontal runs or elbows?
2. Realistic draft reductions due to size of chimney pipe (friction loss of smaller pipe versus larger pipe)?
3. Realistic draft reductions due to chimney caps?
4. Realistic draft reductions possible with a pipe damper?

I know that I am going to have a problem with a 27' chimney on a new install, but it would be nice to be able to calculate the extent of the problem I'll have relevant to the stove I will install.

There is no way to give you realistic numbers for those things. They all play off of each other and changing one variable will change the effects of all of those things. As will house pressures outside barometric pressure temp etc. At 27' I would just plan on 2 key dampers

 

[begreen]

I was wondering if anyone has a picture or used a draft limiter form Pacific Energy? The more I read about the EBT, my understanding is that the stove has a small allowable amount of air flow on the secondary's normally. When the draft increases it sucks open the small baffle allowing extra air in the secondary manifold like a boost mode then closes down again as the fire decreases slowing draft back down. Is my understanding of this correct?

The EBT A and B are explained here.

Sweep's Library - Pacific Energy's Extended Burn Technology

Here's a look at Pacific Energy's EBT technology, as used on several Summit, Neo and Alderlea wood stoves

hearth.com

 

[john26]

The EBT A and B are explained here.

Sweep's Library - Pacific Energy's Extended Burn Technology

Here's a look at Pacific Energy's EBT technology, as used on several Summit, Neo and Alderlea wood stoves

hearth.com

Thank you I read through it a few times and few threads on here with The Chimney Sweep I have a much better understanding of it now. If I could only adapt one to my Lopi LOL.

 

[DBoon]

I would just plan on 2 key dampers

I certainly respect your knowledge and experience in this regard, bholler, but it is puzzling why there is no data available from anywhere that states what draft restriction one key damper will provide under some type of standard operating conditions. In fact, there doesn't seem to be very much data on just about anything relating to chimney drafts, just sort of an "about this" approach and a bunch of rules of thumb. As a technical person, I'd really like to see the math.

 

[bholler]

I certainly respect your knowledge and experience in this regard, bholler, but it is puzzling why there is no data available from anywhere that states what draft restriction one key damper will provide under some type of standard operating conditions. In fact, there doesn't seem to be very much data on just about anything relating to chimney drafts, just sort of an "about this" approach and a bunch of rules of thumb. As a technical person, I'd really like to see the math.

There is no data because there are simply too many variables with a natural draft appliance.

 

[Highbeam]

And not all key dampers are the same. Some have big holes!