Long Burn vs Efficiently

[firebrick43]

First I used the word "may" because there are older designs that do have refinements that may of put them in the same league as modern stove. Very small differences have huge effects.

For example, efi cars actually came out in the mid fifties but was not ready. By the mid/late 80's it had been reintroduced and had a small advancement over the carbureted predecessors but still under 200 hp for a v8. Fast forward 25 years, we have 300 hp v6 engines. The engine uses the same quality of fuel and has the same basic mechanical design. There was no special leap forward in the mechanical side of things, it was very small tweaks invisible to the end user and more computing power available both in the design phase with computer modeling of air and fuel flow and in the ecu to more finely control the engine

Look at fire places. Count rumford developed an efficient fire place in the 1700's. Yet I have never seen one in a modern house.(doesn't mean there are not some out there, just none in the houses I have been in. The differences in many items are small , maybe imperceivable but makes a huge difference in performance.

This applies to to EPA stoves because the EPA regulations demanded that the design was sound and forced the companies to tweak the stove to meet emissions. This does not mean that old stoves didn't happen to be designed to be the most efficient possible, it just means it was somewhat unlikely as the was no need to actually test the results, but now there is. One example I have noticed in EPA stoves is the cleanliness of the glass. Not to say that there were not stove that kept the glass clean, I just can't recall seeing one. Most of the better EPA stove no don't blacken the glass. My jotul will blacken the glass if a piece of wood is against it but will actually self clean(burn it off) once the piece is push away.

 

[Chris-PA]

I make a post arguing that just because a firebox manages to burn 30% more of the fuel available in a stick of wood doesn't necessarily mean you'll get 30% more heat in your home (which I still stand by).

Heat is energy. The energy is in the stick of wood. If the 30% more energy doesn't go into your home, where does it go? Your initial hypothesis was that it went up the flue, but you've denied this now so you 'll have to come up with something else.

EDIT: The 30% number is once again a confusion between an amount of energy and a rate of transfer. I don't really believe the secondary combustion stove extracts 30% more energy from the wood, that would be impressive. Rather, that 30% number that gets talked about is the increase in the rate of heat transfer during secondary combustion. Nevertheless, the question stands: more total energy is being extracted, and at a higher rate during secondary burn - where does it go if it doesn't go into the living space?

 

[1project2many]

I don't believe it's fair to lump all EPA stoves together because, well, they're not the same. Non-cat EPA stoves may be similar in how they achieve clean combustion but there are enough differences so that all should not be judged by the performance of a few.

I've got a small Englander in the house that I bought in '07 or '08. Model 13NC I think? It was cheap and since the installation I've gone from 4-5 cord per year to about 3-3.5 which is great. It keeps the house plenty warm as well with temps in the front room about 74 right now. But there are plenty of downsides.

This stove uses a ceramic shelf to trap heat necessary to support secondary burn. But unless the stove's really hot, you almost have to have flame from your wood touching the shelf for combustion to happen. I've learned how to set up the wood when lighting the stove so secondary combustion happens fairly quickly but the manufacturer didn't provide those tips. Sometimes tossing a small split or two on the coals may not result in secondary combustion, too. And I usually have to get up once between 10:00 and 4:30 to refill the stove or it will stop effectively heating the house. When I do that I need to spend 20 minutes with the stove to get it up to temp before heading back to bed. At this time of year sleep can be hard to come by. I fell asleep tonight at about 9:00 then woke up at 10:20. I've overfilled the stove so I'll let it burn for a bit then damp it down before heading back to bed. That's not optimum timing but it's not too cold out so the timing might work out so I can get more sleep tonight. Worst that will happen is it will be high '60s in the house tomorrow am and I'll need to spend a couple of minutes drawing up some coals from the ashes and restarting the fire.

Regulating temp in the house once its warm involves mixing splits of different species and size. The trick is to maintain enough coals to get the wood to ignite fairly quickly and get to secondary burn without requiring several trips to check the flame and adjust the draft. It's nice when it's really cold because I can get the stove hot then keep running on secondary burn where it burns best. On warmer days the fire often ends up smoldering and that's no fun.
I end up cleaning creosote off the spark arrestor screen a couple of times a year due to this problem although I suspect that reducing the height of the chimney or changing to a different cap might help that. On the plus side, the old stove actually plugged the pipe and this one has never left more than a light coating of creosote in the chimney.

I'm not going to pretend I know the specifics about anyone's home here but as a general rule, if you can heat your basement and make the floors above feel warm, the living space feels warmer. I might be inclined to insulate a basement and warm it as well as heat the air upstairs. It worked in the house I grew up in. Well, it did when we had enough wood to make heat. I also know that I've built a heat exchanger around a wood stove to heat air without drawing heat directly from the wood burner. I used an alternating series of baffles in a duct that surrounded a stove because ultimately, heating by forced air is just a means of moving radiant energy to another location.

I do believe I've read about one type of EPA stove which has a somewhat unique approach to burning wood. Instead of using the wood burner to create heat, the burner is used to gasify and the catalyst provides heat. The owner of one started a couple of threads to brag and claimed ridiculous burn times from this stove which I still don't believe. But the stove does appear to be somewhat unique in its approach. The comment which said the most to me was when a stove manufacturer (or maybe a dealer) said they couldn't compete with this brand of stove in AK where Birch and softwood are all that's available and of course, temps stay low for very long periods. When the stove guy endorses another brand of stove on a public forum it's wise to pay attention.

This winter I ended up with more lighter species than dense wood so I tried using the damper in the flue to extend burn time with the deep cold. What I found is the bed of coals dies out much sooner with the draft reduced to near zero. Maybe I'll play around a bit more but right now I'm back to leaving it open. We close the stove air control almost completely before leaving at 6:30 and 11 1/2 hrs later the house is usually above 60 when my wife gets home. She reports there are usually coals in the firebox so I guess that's not too bad. On weekends when we go into town we usually figure 4-5 hrs max for a trip so there's still plenty of heat in the box when we get back. I do miss the longer burn times of the old stove. But using less wood and having a cleaner exhaust are very good marks on the plus side of the list. If I choose to replace this stove I'll be looking to find a design that gives the same results with more time between refills. I don't anticipate buying a smoke dragon.

Well, 12:00 so I'll toss another small split or two on top of the fire then head to bed.

 

[Whitespider]

If the 30% more energy doesn't go into your home, where does it go? Your initial hypothesis was that it went up the flue, but you've denied this now so you 'll have to come up with something else.

No, it was not my initial (as you say) "hypothesis" that burning 30% more of the available fuel resulted in all of it exiting the flue. I simply posted if all else remains equal, a hotter firebox temperature results in hotter flue gasses... and hotter flue gasses equal more heat exiting the flue. No matter how you twist it, that's all I posted... and I ain't denied it. The only thing I've denied is what you've attempted to twist it into.

You claim flue temperature runs cooler with your EPA box, I claim mine ran hotter... I ain't callin' you a liar, I actually addressed that in my post. That still doesn't change the simple fact that, if all else remains equal, increasing firebox temperature also increases flue gas temperature... and, if all else remains equal, increasing combustion air volume also increases flue gas volume. And another simple fact is, increasing either one, or both, results in more heat exiting the flue. If your wonder-stove achieves secondary burn running on near zero combustion air (primary and secondary), and at the same time pumps out massive BTU's while running ultra-low flue temperatures... well... I guess we're back to magic.

In hindsight... I should have just stuck with my original "magic" post on page one.
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[cmsmoke]

You should have been a sports caster or a scratched record.

 

[Chris-PA]

No, it was not my initial (as you say) "hypothesis" that burning 30% more of the available fuel resulted in all of it exiting the flue. I simply posted if all else remains equal, a hotter firebox temperature results in hotter flue gasses... and hotter flue gasses equal more heat exiting the flue. No matter how you twist it, that's all I posted... and I ain't denied it. The only thing I've denied is what you've attempted to twist it into.

You claim flue temperature runs cooler with your EPA box, I claim mine ran hotter... I ain't callin' you a liar, I actually addressed that in my post. That still doesn't change the simple fact that, if all else remains equal, increasing firebox temperature also increases flue gas temperature... and, if all else remains equal, increasing combustion air volume also increases flue gas volume. And another simple fact is, increasing either one, or both, results in more heat exiting the flue. If your wonder-stove achieves secondary burn running on near zero combustion air (primary and secondary), and at the same time pumps out massive BTU's while running ultra-low flue temperatures... well... I guess we're back to magic.

In hindsight... I should have just stuck with my original "magic" post on page one.
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All else does not remain equal, this is an irrelevant distraction having nothing to do with the issue. A secondary combustion stove works by greatly restricting the primary air. The hot coals cook off the volatile gasses from the wood, which hit the hot air coming down from the manifold above and ignite. So by reducing the primary air the fire gets hotter. Apparently to you this is magic.

If you want to know how much heat (energy) goes up the flue you'd need to look at both the temperature and the volume of gases (actually the mass). You could have a low volume of very hot gas.

On my stove there is one inlet for both primary and secondary air. This is the opening wide open:

And this is it during a secondary burn (lousy photo angle, sorry):

 

[Whitespider]

So by reducing the primary air the fire gets hotter. Apparently to you this is magic.

Well yeah... magic.
If I'm understanding this...
If reducing primary air makes the fire hotter, then increasing it must make the fire cooler... so you should be able to run your stove with with a full fuel load and the primary wide-azz-friggin'-open without over-firing it ‼ Yup, I'll call that magic... every time ‼

I don't have a magic EPA stove.
Mine has two separate inlets, one for primary, one for secondary, controlled in tandem by a single operating lever. Every time I increase combustion air via the lever (open both inlets) the fire gets hotter, and every time I decrease combustion air via the lever (close both inlets) the fire gets cooler... every time ‼ I tried running them separately, by disconnecting the linkage; it didn't matter squat which inlet I opened, the fire got hotter, and it didn't matter squat which inlet I closed, the fire got cooler... every time ‼ But I did gain a slightly longer burn (heating) time, with less coaling issues, by reducing the secondary slightly in relationship to the primary.

I guess Pacific Energy hasn't hired a magician yet... they really should check into that.
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[Chris-PA]

Well yeah... magic.
If I'm understanding this...
If reducing primary air makes the fire hotter, then increasing it must make the fire cooler... so you should be able to run your stove with with a full fuel load and the primary wide-azz-friggin'-open without over-firing it ‼ Yup, I'll call that magic... every time ‼

I don't have a magic EPA stove.
Mine has two separate inlets, one for primary, one for secondary, controlled in tandem by a single operating lever. Every time I increase combustion air via the lever (open both inlets) the fire gets hotter, and every time I decrease combustion air via the lever (close both inlets) the fire gets cooler... every time ‼ I tried running them separately, by disconnecting the linkage; it didn't matter squat which inlet I opened, the fire got hotter, and it didn't matter squat which inlet I closed, the fire got cooler... every time ‼ But I did gain a slightly longer burn (heating) time, with less coaling issues, by reducing the secondary slightly in relationship to the primary.

I guess Pacific Energy hasn't hired a magician yet... they really should check into that.
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True, without an IR thermometer I don't actually know if the fire gets hotter or not, but I do know the stove gets hotter (and transfers heat energy into the room at a greater rate) and the flue gets cooler. Sorry for the sloppy terminology. If I opened the intake wide during secondary burn, there might indeed be localized spots that were hotter, and the flue would get really hot.

But again, the real issue is not what happens when a stove is misoperated/overfired, as that is not how either type of stove is used. Rather it's whether these stoves heat a room better than a smoke dragon, which you maintain they don't. Except you recognize that they extract more energy from the wood (based on reduced unburned particulate emissions tests), and we know that during secondary combustion the rate of energy transfer is higher. I'm still waiting to hear where the increased energy extracted from the wood goes if it doesn't go into the home and it doesn't go up the flue?

 

[cmsmoke]

I'm with Chris all the way.
On my stove the secondary air tube is always open. It is 2" square tubing that runs up the back corner of the stove, once it reaches the top, it makes a 90 degree turn and runs along the top rear of the stove. There are three holes in it which accept the round burner tubes. The air is heated as it travels to the burn tubes. There is vermiculite lining the ceiling of the stove, which keeps the heat from being absorbed by the stove and keeps it concentrated in the burn tube area. Once the thermostatic spring gets warm enough to close the primary air most of the way, secondary combustion takes place and will self support itself until the volatiles are used up. This can last several hours, depending on the fuel load. The secondary air pulled in is dictated by flue draft...too much draft will draw in excessive air and cause a cool down, which will cause a short lived secondary burn. Lack of draft will cause a weak secondary burn, which won't keep the heat level high enough to support itself. Either way the longevity of efficiency will suffer.
The only magic around here is the claim of a secondary burn in a stove or furnace that has no provision to supply oxygen to the so called area that secondary burn would take place. Three things are needed for combustion. Fuel (volatiles), Ignition (enough heat held in place by insulation) and oxygen (supplied by secondary air). There is no way to prove this happens without a glass door. Just because there is a lack of smoke, it doesn't mean you are achieving secondary burn. You can make a campfire look to burn clean, once it is hot enough.

 

[flotek]

My old furnace had a baffle and above this shelf was the flue exit. . My new EPA furnace has far more involved above the stainless burn tubes than a simple baffle plate and some burn tubes it has a thick high temperature ceramic baffle then an above that is an advanced heat exchanger separate area. Made of steel ( a special drop down door allows access for quick cleaning of this area) with several large round steel pipes to route the gasses and extract all the heat . Before it exits the main pipe out the rear. .. By the time it goes out to the flue pipe the temperature is only 150-200 degrees in fact you can literally put your hand on it with a full on fire in the box . That is a good indication your getting all the heat available out of the wood and not heating the great outdoors by sending btus up out your flue

 

[Whitespider]

The only magic around here is the claim of a secondary burn in a stove or furnace that has no provision to supply oxygen to the so called area that secondary burn would take place. Three things are needed for combustion. Fuel (volatiles), Ignition (enough heat held in place by insulation) and oxygen (supplied by secondary air). There is no way to prove this happens without a glass door. Just because there is a lack of smoke, it doesn't mean you are achieving secondary burn. You can make a campfire look to burn clean, once it is hot enough.

LOL... Spoken like a true believer.

First of all, the "fuel" secondary combustion is intended to burn is not the "volatiles", secondary combustion is intended to burn particulate matter the primary burn leaves unconsumed during combustion of the "volatiles".

You believe (or assume) that the only way to make a fire burn "clean" is with some sort of secondary combustion activated by some sort of secondary air supply... when your campfire example shows just the opposite. The reason a campfire will look to be burning clean (without smoke) is simply because it is. A campfire pretty much has an unlimited supply of air (oxygen), and when it gets hot enough... well... no magic, it achieves closer to complete combustion.
So, does that mean the campfire is burning as clean as your stove?? The answer ain't a simple yes or no. When both are at the "no smoke" stage I would bet the difference ain't all that great... but the secondary combustion stove is designed to get there faster, meaning it would certainly be "cleaner" over the complete fuel load combustion process.

A "clean", smoke-free burn does not require secondary combustion activated by a secondary air supply... given enough heat and oxygen primary combustion is more than capable. The issue was never that an older, well designed stove couldn't achieve "clean" burn, the issue was people ran them poorly causing "dirty" burn... and yes, there was also cheap, poorly designed stoves (and there still is). I'm not saying the older, well designed stoves burned as super clean as the newer secondary burn stoves are capable of when run perfectly... but much like the campfire, when both are at the "no smoke" stage I would bet the difference ain't all that great. The newer stoves are designed to get there faster and make a "dirty" burn less likely... they make it less likely an idiot can screw-it-up. And don't forget, the current EPA test procedures allow a stove to fail the low burn test... your fancy, new-fangled stove may not be as clean as you believe when it's stopped down to low setting.
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[Whitespider]

Oh yeah... and don't forget...
Combustion efficiency does not automatically equal heating efficiency.

And because I've taken so much heat for that statement, here's a direct quote from chimneysweeponline.com...

"Thus, even a model with an unusually low Emissions rating doesn't necessarily score a high Heating Efficiency rating."
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[naturelover]

A campfire or stove can not burn as clean as an EPA stove.

Part of its design is to keep particulates in the stove. The trick is to get enough uncontrolled draft to burn the wood cleanly, but not have any ashes and such escape through the flue, along with keeping the gases they need to burn off inside the stove.

Part of the EPA test procedure is to filter the flue gases for particulates.

(Info from one of the reps for a stove manufacturer)


Sent from my iPhone 5 using Tapatalk

 

[flyboy553]

There needs to be separate forums for EPA stoves and NON-EPA stoves! And if a disciple of one goes in the other, they can get charged with bullying!

Ted

 

[Chris-PA]

Oh yeah... and don't forget...
Combustion efficiency does not automatically equal heating efficiency.

And because I've taken so much heat for that statement, here's a direct quote from chimneysweeponline.com...

"Thus, even a model with an unusually low Emissions rating doesn't necessarily score a high Heating Efficiency rating."
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"Heating Efficiency" is a term applied primarily to heat pumps, and is a measure of long term (seasonal) energy out vs energy input. It has nothing to do with output capacity, rather just how much of the energy it consumes is transferred into the living space over a long invterval.

The EPA particulate tests capture the particulate mass over the entire burn and compare that to the mass of the firebox load - how much of the wood went up the stack as particulates. The alternative to going up the stack as unburned particulates is being burned and releasing the energy, so the measure of the percentage of particulates going up the stack is directly related to the percentage of the energy that went up the stack. It would be quite difficult to reduce the unburned particulates without increasing the efficiency of the conversion of the wood energy into heat.

Therefore, the statement you quoted is gibberish. A lower particulate emission rating is directly related to a higher "Heating Efficiency".

None of these measures are rates of heat (energy) transfer, so they tell you nothing about how warm your house will get.

 

[Whitespider]

"Thus, even a model with an unusually low Emissions rating doesn't necessarily score a high Heating Efficiency rating."

How could that possibly be any friggin' clearer??
Oh yeah... I forgot... magic.
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[Chris-PA]

There needs to be separate forums for EPA stoves and NON-EPA stoves! And if a disciple of one goes in the other, they can get charged with bullying!

Ted

I decided I am going to simply correct (hopefully with patience) the constant stream of gibberish and erroneous pseudo-science being pumped out this topic. This continual mixing of unrelated measurements to calculate nonsense and throwing about terminology that sounds important but means nothing is an attempt to support a predetermined (erroneous) conclusion. People read this junk and think it means something, and then make misinformed decisions. I think it is wrong to misinform people either intentionally or through ignorance.

There is a lot of confusion out there on these topics, and the EPA emissions tests actually make it worse (they measure a quantity and a time, convert it into a rate, and set the limits as a rate - but they don't even care about the rate, they care about the amount!). The rate of energy transfer is what determines if you are warm - if your stove is transferring energy into your living space at rate greater than the house is losing it to the outside then you will be warm. The efficiency and emissions ratings don't tell you anything about this.

 

[Chris-PA]

"Thus, even a model with an unusually low Emissions rating doesn't necessarily score a high Heating Efficiency rating."

How could that possibly be any friggin' clearer??
Oh yeah... I forgot... magic.
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You posted that already, with no definition of terms. I defined the terms and explained that it is obviously incorrect. Rather than post it again, why don't you explain what you think it means, and how that would work?

Once again, where does the additional energy from burning more of the original fuel load go if it does not go into the living space?

 

[Whitespider]

I think it is wrong to misinform people either intentionally or through ignorance.

At least we agree on something...
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[Chris-PA]

At least we agree on something...
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Where does the energy go?