Measuring Chimney Draft

[CaseyForrest]

Again, it's not about burning less wood. It's about burning ALL the fuel which is what cat stoves are designed to do. Burning less wood over THE SAME amount of time is the proper context.

I'm not, nor do I believe anyone else, is going to dispute the math. Numbers aren't my thing.

But you're arguing less wood over a longer period of time. That's not a valid rebuttal because that's not the argument. It's about burning the same amount of wood over a longer period. This is accomplished by using a catalyst which finishes the burning cycle of the byproducts of the main fuel load.

No one, I would expect, is loading a catalytic stoves firebox half full and expecting it to burn longer than if it was loaded full. That's simply not possible. So technically the argument as you are framing it is technically correct.

But no one is doing that. And if they are while expecting magical results, well.......

sent from a field

 

[Whitespider]

I agree with Casey. Getting more heat out of the fuel that is being burnt meant more heat into the house per volume of wood consumed. The end result is you burn less fuel to heat the same space.

But if it isn't producing the amount of heat per hour that you require... what good is the efficiency??
I heat my entire home with my wood furnace... that's a big space... that requires a lot more heat per hour than heating one or two rooms.

Let's go back to your original post in this thread...

My new King is a little sluggish and I want to measure it and make sure that is the problem. So far I'm not impressed with the heat output unless I bypass the cat, open the door and get the fire roaring and close the door and engage the cat. It seems to slowly dwindle.

But you're arguing less wood over a longer period of time. That's not a valid rebuttal because that's not the argument. It's about burning the same amount of wood over a longer period.

That is exactly what my math showed... the same amount of wood over a longer period.
Both were loaded with 50 pounds of wood... the Blaze King running on the high setting (max output for the time period Blaze King says it will run).
I said it even gets worse when both less wood and longer time period is claimed... which is often the claim made.

No one, I would expect, is loading a catalytic stoves firebox half full and expecting it to burn longer than if it was loaded full. That's simply not possible. So technically the argument as you are framing it is technically correct.

First of all, I didn't make that argument... however, the Blaze King box is smaller than my DAKA box, but the math assumed the same amount of wood loaded into them. If I pack my DAKA plumb full I can get anywhere from 12 to 20 hours depending on heat demand.
Second, at the same stove setting a firebox loaded half full will burn just as long a a fire box loaded full (at least, close enough for this argument)... it just produces less heat during that time. A stick of wood burns at a certain rate (controlled by the stove setting)... it don't matter if there's 5 more sticks in the box with it, or 15 more sticks in the box with it.
Typically a stove is loaded with more wood so the stove setting can be throttled back to achieve a slower burn rate, at the same heat rate from less wood at a higher burn rate. That doesn't change in any stove... old or new. Stove setting determines how long the fuel load burns... not the size of the fuel load itself.
*

 

[Whitespider]

Again, it's not about burning less wood. It's about burning ALL the fuel which is what cat stoves are designed to do.

You're completely missing my point...
I agree, that efficiency is wonderful and great if you're warm enough.
But if you're friggin' cold what good is the efficiency?? If you need a higher rate of heat output, then you need a higher rate of heat output... period. At that point the most efficient fuel consumption that will provide the required rate of heat output is the most efficient heater for your needs.

This ain't complicated... I'm talking about matching the per hour rate of heat output to your requirements... that is the first concern, after that you look for the most efficient that can provide that rate of heat output.
Just as shopping for a vehicle to pull your loaded 16 ft trailer... power on demand is the first concern, once you narrowed it down to those with the required power you can start looking at fuel efficiency among those only. A Ford Fiesta ain't gonna' cut it... neither is a sports car... you need a truck.
*

 

[Marshy]

Let's take the Blaze King in question... with a efficiency rating of 88% LHV/82% HHV. Now let's say under real world conditions/operation the operator actually gets 85% (I believe I'm being generous). We load the stove with 50 pounds of wood and use the value of 7000 BTU's per pound (just picking numbers for comparison... it doesn't change the result).
7000 x 50 x .85 = 297,500 BTUs.
Blaze King says the stove will run for 12 hours on the high setting. (Are you gonna' run it on high??)
297,500 / 12 = 24,791 BTUs per hour (averaged).
Now lets throttle it back so it runs 16 hours...
297,500 / 16 = 18,593 BTUs per hour (averaged).

Now let's take an older style stove and say we can get 60% efficiency from it.
7000 x 50 x .60 = 210,000 BTUs.
Most any older style stove will run 6 hours without any problem (my DAKA furnace will easily).
210,000 / 6 = 35,000 BTUs per hour (averaged)
And let's throttle it back to run 9 hours...
210,000 / 9 = 23,333 BTUs per hour (averaged).

Notice the older style stove produced 10,000 more BTUs per hour of run time... but ran a shorter time.
Another issue with the newer style is the heat output is not as consistent over the entire burn cycle... the output drops way off late in the cycle (however, I don't have experience with cat stoves in that respect).
It is not possible to do both... burn less wood, over a longer period, and get the same per-hour rate of heat generated.
Even at 50% efficiency the older stove makes more heat per hour.
7000 x 50 x .50 / 6 = 29,166 BTUs per hour.
7000 x 50 x .50 / 9 = 19,444 BTUs per hour.

And that's just figuring the burn cycle time... when you start saying your loading less wood and burning it over a longer time... the numbers look a whole lot worse.

If the newer, higher efficiency stoves will produce the amount of heat per hour that you require... the efficiency is wonderful and great.
If they cannot produce the amount of heat per hour that you require... all the efficiency in the world is worthless.
Just as you'll get great fuel efficiency in a Ford Fiesta... but it won't pull your trailer.

There ain't no magic... never has been.
*

Your argument is flawed Spidy and here is why...

Assume the newer high efficiency stove heat output per hour satisfies your highest heating demands. Anything more (BTU/hr) by the older stove is not needed and will go unused.
Do you agree this is a real world assumption. People don't run their OWB WFO to heat 3000 sqft when it is sized to 4-5000 sqft, right?

Okay, let's look at the math now. I like numbers.


In my math I assumed the old stove is 50% efficient and I believe that might be generous. Regardless of the exact efficiencies of the stoves, the higher efficiency stove will burn less wood in the same time frame at the same heat output. The difference is 50lb vs 85lbs.

 

[Marshy]

But if it isn't producing the amount of heat per hour that you require... what good is the efficiency??
...
Let's go back to your original post in this thread...
*

You are exactly right, the appliance needs to meet the heating demand otherwise what good is it? I wouldn't keep the stove if it wasn't meeting my demand. With any new appliance there is a learning curve. I found the stove perfor.Ed better once I sealed up my cleanout door and a big leak at one of my spare thimbles. Having the proper draft helped the stoves combustion and was no longer get sluggish. I also found out that a fan on the stove is necessary to get the heat off the surfaces in order for it to heat the space. The stove doesn't radiate the heat like my old stove. Once I get the fan kit I believe I will be even more satisfied with the stove.

That is exactly what my math showed... the same amount of wood over a longer period.
Both were loaded with 50 pounds of wood... the Blaze King running on the high setting (max output for the time period Blaze King says it will run).
I said it even gets worse when both less wood and longer time period is claimed... which is often the claim made.*

We agree, I even said the older stoves have a higher BTU/hr than the newer stoves however, we have to assume the high efficiency stove is sized properly to the demand or none of this is worth discussing. In a sense, the math you did is pointless because if a person is willing to live with an undersized appliance then they are willing to live in the cold. I'm not. That is why my example is a valid real world scinero.

First of all, I didn't make that argument... however, the Blaze King box is smaller than my DAKA box, but the math assumed the same amount of wood loaded into them. If I pack my DAKA plumb full I can get anywhere from 12 to 20 hours depending on heat demand.
Second, at the same stove setting a firebox loaded half full will burn just as long a a fire box loaded full (at least, close enough for this argument)... it just produces less heat during that time. A stick of wood burns at a certain rate (controlled by the stove setting)... it don't matter if there's 5 more sticks in the box with it, or 15 more sticks in the box with it.
Typically a stove is loaded with more wood so the stove setting can be throttled back to achieve a slower burn rate, at the same heat rate from less wood at a higher burn rate. That doesn't change in any stove... old or new. Stove setting determines how long the fuel load burns... not the size of the fuel load itself.
*

There is some influence on the size of the splits and the burn time IMO. That seemed way more obvious to me with my old stove than my new stove. When you have a thermostatic crolled stove it tried to levelize the heat output by controlling the combustion air. I usually leave my stoves thermostat in one position and load the stove accordingly to the weather. If it's 34F out then 4 splits might last 8 hours. If it's 20F then ever 4 hrs. If your stove is not automatically controlling combustion air it's hard to compare they two. How many cuft is your stoves firebox? A furnace stove is generally larger than a free standing stove as they typically have a higher heat output also. Burn times and comparisons between the two become fuzzy at best but we can compare them on paper quite easily.

 

[Whitespider]

Your argument is flawed Spidy and here is why...

No it is not... you are not arguing the same thing.

Assume the newer high efficiency stove heat output per hour satisfies your highest heating demands. Anything more (BTU/hr) by the older stove is not needed and will go unused.
Do you agree this is a real world assumption.
...the higher efficiency stove will burn less wood in the same time frame at the same heat output.

No, I don't agree with any of that... because you're arguing something different than I am...

1. My argument assumes the newer high efficiency stove heat output per hour does not satisfy your highest heating demands... that is the whole damn point. I've already stated that if the newer style stove does satisfy your highest heating demands, the efficiency is wonderful and great.
2. My argument assumes the potentially higher rate of heat output of the older stove is needed... that is the whole damn point. I've already stated that if the newer style stove does satisfy your highest heating demands, the efficiency is wonderful and great.
3. My argument ain't about the same rate of heat output, it is about a higher rate of heat output when required... that is the whole damn point. I've already stated that if the newer style stove does satisfy your highest heating demands, the efficiency is wonderful and great.

We agree, I even said the older stoves have a higher BTU/hr than the newer stoves however, we have to assume the high efficiency stove is sized properly to the demand or none of this is worth discussing.

But that was the whole damn point.
The Blaze King is one of the very best for heat rate output... is it not?? Well, you're the one that posted in the original post of this thread...

My new King is a little sluggish and I want to measure it and make sure that is the problem. So far I'm not impressed with the heat output unless I bypass the cat, open the door and get the fire roaring and close the door and engage the cat. It seems to slowly dwindle.

That's what I'm addressing...
I can flat tell you by the math that the Blaze King would not satisfy my heat output requirements when it's -15°, at night, with a 45 MPH wind blowing... it flat ain't gonna' keep my house (the entire house) at 70° over night, it don't have the required rate of heat output... the house would slowly cool and I'd wake up freezing. And the "dwindling" heat output would make things even worse... I need a continuous and constant rate of heat output when the conditions are like that. Can you point me to a newer style firebox that significantly outperforms the Blaze King, "King"?? When I need the heat... I need the heat... anything less than what I need is not what I call efficient. When I don't need maximum heat, I load the firebox with less wood... when I need more heat I load the firebox with more wood... and when I need maximum heat I load the box with even more wood... and my (so-called) smoke dragon makes a ton of friggin' heat when required (however, I don't believe I've ever ran it at "max" output except to bring the house up to temperature after being away for a couple days).
*

 

[Del_]

My argument assumes the newer high efficiency stove heat output per hour does not satisfy your highest heating demands... that is the whole damn point. I've already stated that if the newer style stove does satisfy your highest heating demands, the efficiency is wonderful and great.

An argument based on a wrong assumption is what we have here.

 

[CaseyForrest]

You're completely missing my point...
I agree, that efficiency is wonderful and great if you're warm enough.
But if you're friggin' cold what good is the efficiency?? If you need a higher rate of heat output, then you need a higher rate of heat output... period. At that point the most efficient fuel consumption that will provide the required rate of heat output is the most efficient heater for your needs.

This ain't complicated... I'm talking about matching the per hour rate of heat output to your requirements... that is the first concern, after that you look for the most efficient that can provide that rate of heat output.
Just as shopping for a vehicle to pull your loaded 16 ft trailer... power on demand is the first concern, once you narrowed it down to those with the required power you can start looking at fuel efficiency among those only. A Ford Fiesta ain't gonna' cut it... neither is a sports car... you need a truck.
*

You're talking about something no one else is.

sent from a field

 

[CaseyForrest]

And what the hell does the efficiency or heat output of a blaze king stove have to do with draft?

Seems someone, or 2, found a soapbox to get on.

sent from a field

 

[Marshy]

No it is not... you are not arguing the same thing.

No, I don't agree with any of that... because you're arguing something different than I am...

1. My argument assumes the newer high efficiency stove heat output per hour does not satisfy your highest heating demands... that is the whole damn point.
2. My argument assumes the potentially higher rate of heat output of the older stove is needed... that is the whole damn point.
3. My argument ain't about the same rate of heat output, it is about a higher rate of heat output when required... that is the whole damn point.

Yes your argument is flawed, I just showed you in one case why. My previous example is how things really work when the appliance is properly sized and why efficiency allows you to get a longer burn time for the given amount of wood. The end result is more BTU's make it into the living area per load of fuel and if the appliances can perform at the same rate (btu/hr) then the higher efficiency stove will produce heat for a longer time per load of fuel. Those are thermodynamic laws.

I recognize we are arguing a different point but what I am trying to tell you is that I don't believe your argument is valid or applicable to my situation. You are assuming that the stove cannot meet my demand but what I am saying is that I believe it can meet my demand to keep me comfortably warm. I wasn't sure it could put out enough at first and created this thread to help me rule out potential issues like poor chimney draft. Like I previously said, I found some leaks in my chimney that hurt draft. I also don't believe the chimney mass was up to temperature which was hurting draft and it was warmer out (40's). I also wasn't using any fans to more the heat off the stoves surface and was expecting it to be able to radiate the heat like my old stove. They wont radiate like the old Shenandoah.

But that was the whole damn point.
The Blaze King is one of the very best for heat rate output... is it not?? Well, you're the one that posted in the original post of this thread...*

Who said it "is one of the very best for heat output"? I certainly did not say that and I did not buy it because it had the highest amount of BTU's in a given hour.

If you haven't looked at several stove companies specs and noticed yet, it becomes very hard to tell how the stoves really perform in the real world. BK stoves do not list a peak output in BTU/hr of the stove like all other manufacture do. They only list an average BTU/hr for a 12 hr burn time which is a lot less than the peak output claimed by everyone else (obviously). That alone makes it hard to understand peak performance but what does the peak performance mean and why is it useful in choosing a stove? I'm not sure it is. A stove wont operate at peak for much longer than one or two hours so whats the value in knowing that? Why don't the other manufactures list an average BTU/hr for a 12hr cycle (or 4, or 6!) so people can understand how they perform? Its only a guess for me why someone might think peak output is helpful in determine a stoves size. In an ideal world you could look at a performance graph of the stoves output at 100, 75, 50, 25, and 0% operating settings and see what the performance is. Knowing your houses heat loss would allow you to compare it to the stoves performance and shed more light on how often you can expect to refuel the stove. Here's what it might look like.


You can see by the graph that if your heating demand it 90K BTU/hr then the stove will only by able to meet of exceed your demand for a few hours. If your demand is 100K BTU/hr then this stove is undersized for your application. If its 52K then you have a lot of operating margin on the stove and it will have plenty of horsepower (like a duramax) to keep you warm.

That's what I'm addressing...
I can flat tell you by the math that the Blaze King would not satisfy my heat output requirements when it's -15°, at night, with a 45 MPH wind blowing... it flat ain't gonna' keep my house (the entire house) at 70° over night, it don't have the required rate of heat output... the house would slowly cool and I'd wake up freezing. And the "dwindling" heat output would make things even worse... I need a continuous and constant rate of heat output when the conditions are like that. Can you point me to a newer style firebox that significantly outperforms the Blaze King, "King"?? When I need the heat... I need the heat... anything less than what I need is not what I call efficient. When I don't need maximum heat, I load the firebox with less wood... when I need more heat I load the firebox with more wood... and when I need maximum heat I load the box with even more wood... and my (so-called) smoke dragon makes a ton of friggin' heat when required (however, I don't believe I've ever ran it at "max" output except to bring the house up to temperature after being away for a couple days).
*

We get it, it's not your cup of tea. Its undersized for your application and therefore you don't care about its efficiency. Thanks for your input.

 

[Marshy]

And what the hell does the efficiency or heat output of a blaze king stove have to do with draft?

Seems someone, or 2, found a soapbox to get on.

sent from a field

LOL actually, the only tie is too little of a draft will cause low performance of the appliance and too much draft will cause short burn cycles. That's it.

 

[Whitespider]

You're talking about something no one else is.

Good lord man...
I came back to this thread because quotedraven quoted my post (from page 3)... I addressed his post... and then you quoted that one.
If quotedraven wasn't addressing my argument... what the hell was he addressing??
This is how it went...

There ain't no magic... never has been.
I hate to sound like a broken record... but... you flat cannot burn less fuel, over a longer time period, and get the same per-hour rate of heat generated... it ain't possible.
Marshy, I'm seriously sorry you're having troubles, but you're attempting to use what amounts to a space (room) heater to heat more space than it can... the more space you heat, the higher per-hour rate of heat output needed, something that cannot be accomplished in an appliance designed to both burn less fuel, and burn it over a longer time period.
Been there... tried that... failed.

Efficiency efficiency efficiency

A Ford Fiesta is fuel efficient... but you ain't gonna hook your loaded 16 ft trailer to it.
Efficiency is worthless if it cannot provide the power required to do the job.
You flat cannot burn less fuel, over a longer time period, and get the same per-hour rate of heat generated... it ain't possible.
There ain't no magic... never has been.

Lord knows I could be wrong...
I believe the shtick with catalytic stoves isn't that they are burning less fuel, its that they are burning all (or most of) the fuel.
You can see it even with a non catalytic stove that has secondaries over one that doesn't, or compared to an open fireplace. Less smoke out of the end of the chimney equals more fuel being burnt in the firebox.

My argument has not changed since page 3... after which I dropped it... until quotedraven , you , and Marshy argued with my argument... by arguing something different than mine.

I ain't arguing the newer stoves extract more heat from a given quantity of fuel... I know they do... but they do it over a longer burn cycle which reduces the per hour rate of heat output... it-is-what-it-is.
So I'll say it again, and then I'll drop it again...
You flat cannot burn less fuel, over a longer time period, and get the same per-hour rate of heat generated... it ain't possible.
There ain't no magic... never has been.
*

 

[Whitespider]

You can see by the graph...

Your graph is not the same thing I was arguing.
I was not arguing how much heat output there actually is... I was arguing which appliance is capable of producing more heat per hour when required to do so. I can change the per hour rate in my calculations by simply changing the quantity of fuel... the exact output number ain't needed to make my point, only the comparison.

I used a specific amount of fuel (50 pounds) in each appliance to make a comparison... I even stated, "just picking numbers for comparison... it doesn't change the result" (the resulting being a higher rate of heat output per hour of run time for a given quantity of fuel loaded in each). That's also why I used the "high" setting on the Blaze King (which is said to run 12 hours) verses the 6-8 hours for the smoke dragon running at a "high" setting. I'm not concerned with run time, I'm concerned with the rate of heat output while it's running (that was the comparison I was making). And in my furnace, output rate does not drop off during the cycle like your graph illustrates, it stays relatively constant and even between loadings... the air forced under the coal bed keeps it screamin' hot. I control the heat output of my furnace by the amount of fuel loaded, I make no changes to my furnace other than the quantity of fuel loaded. If I expect a higher heat demand I load a little more, if I expect less demand I load less... if the circulation blower cycles on-'n'-off 3-4 times an hour, and the draft blower kicks on every 1½-2 hours or so for a couple minutes... I've got it running just about perfect. Around 95% of the time I load it twice a day, morning and evening... and never look at between those loadings.

Tell me how many pounds of fuel is used to produce your graph, and I'll run the numbers against a (so-called) smoke dragon again. But if you don't know the quantity of fuel used, the graph cannot be used to make a like comparison... it's just arbitrary numbers.

And by-the-way, a smoke dragon run correctly is more than capable of 60% efficiency... if run incorrectly not so much.
If you load them up and choke them down, your efficiency goes to crap... that ain't how I run mine... and it don't make smoke, or creosote.

And one more by-the-way...
Your graph shows an average of 51,582 BTU's per hour, for 12 hours?? At 88% efficiency??
Do you realize that works out to something well over 100 pounds of air-dried firewood?? Well over 100 pounds.
Can you get something well over 100 pounds of cut and split firewood in your Blaze King?? (For reference, I could in my furnace fairly easily, but I never have.)
*

 

[Whitespider]

You know what @Marshy ... if we figure 7000 BTU per pound of wood, at 88% efficiency, for 12 hours (highest setting) it works out almost exactly 100 pounds of wood to average your 51,582 BTUs per hour.

So let's run the numbers in my smoke dragon figuring 60% efficiency (hey, your graph is pretty optimistic at 88% for real world)...
100 pounds x 7000 x .60 / 6 hours (high setting) = 70,000 BTUs per hour... a greater rate of 18,418 more BTUs per hour at the cost of twice the wood over 12 hours (but that's at max output, where the cost is significantly the highest... throttle them both back and the BTU gain to cost ratio changes).
And don't forget... the heat stays pretty steady, constant, and even in the smoke dragon, it don't start out way above the average and ends up well below as the cycle completes. If it did, my house would not stay a constant 70°-71°, day in and day out, no matter what the heat demand is.

And even at 50% efficiency (but to be fair we'd need to drop the Blaze King down to a more real world 80% or a bit more, say 82%??)...
Blaze King - 100 x 7000 x .82 / 12 = 47,833 BTUs per hour
Smoke Dragon - 100 x 7000 x .50 / 6 = 58,333 BTUs per hour... still a greater rate of 10,500 more BTUs per hour at the cost of twice the wood over 12 hours (but that's at max output, where the cost is significantly the highest... throttle them both back and the BTU gain to cost ratio changes).

 

[quotedraven]

The efficiency changes when you throttle down the smoke dragon hence the name. If all the wood just smoldered then most of your fuel would go wasted up the chimney as smoke.

 

[Marshy]

FFS @Whitespider, let's start a new thread on stove efficiency so we can continue this. We both agree you are arguing a completely different set of assumptions and we both agree that the older stove out out more peak BTU/hr. Why are we continuing this conversation then?

The graph I made is to illustrate that the BK stove might actually put out the same peak BTU/hr as an older stove. We just arnt sure because the manufacturer only gives us a spec for average BTU/hr in a 12 hr cycle, not peak output. The real operating profile of the BK stove could resemble the curve on the graph where is peaks to 125k BTU and tapers off over 12 hrs. The point I was making with the graph is once the operating output of the stove drops below the heat demand of your living space (orange, green or blue lines) then demand is greater than supply for your living environment and more fuel will be required shortly thereafter.

 

[Whitespider]

The efficiency changes when you throttle down the smoke dragon hence the name. If all the wood just smoldered then most of your fuel would go wasted up the chimney as smoke.

Agreed... smoldering is a poor way to run any firebox, and that ain't how I've ever run any of mine.
The only thing I would disagree with (and it's splitting hairs) is that you can "throttle down" and increase efficiency, as long as you don't throttle down so much that you're choking them.
There's a "sweet spot" (or range) where they run the best; once you find it, the only adjustment you need to make is the quantity of wood you load into it... a larger load will create more heat per hour, a smaller load makes less heat per hour, but burn rate remains the same regardless of the load.

And if truth be told... the poor efficiency attributed to them ain't about the firebox itself, it's more about operator error.

Why are we continuing this conversation then?

LOL
We're not
*

 

[Marshy]

I think its an interesting topic and Im willing to continue it, just not in this thread.

Here, http://www.arboristsite.com/community/threads/woodstove-efficiency-debate.304587/

 

[Motorsen]

So Marshy, have you measured your draft after bettering all issues and cleaning the screen on your chimney???

 

[Marshy]

So Marshy, have you measured your draft after bettering all issues and cleaning the screen on your chimney???

The draft was measured with a tight chimney and up to operating temperature and was found to be 0.045" wc. The cap was on but the screen was clean at the time because it had only ran for a couple weeks.

I haven't checked it since the first time but believe with the colder weather its draft is reaching the 0.05" wc. Im going to crawl in my attic and shoot the IR gun on the masonry chimney and see how much heat it is radiating. The chimney passes from the basement all the way through the attic. It has its own chaseway through the main floor that is open to the attic (ranch home on basement). Im interested to see how much of a thermal difference is between the bottom and top, and what the temp is at the very top before the cap (while remaining in the attic). I suppose I could climb on the roof, take the cap off and check the clay liner inside surface temp. I don't want to be that close to the chimney with the stove running full open though, I'd get a face full of smoke.