'Ideal' Draft ?

[Peter B.]

I've been burning wood quite awhile, but have never owned or used a manometer to check my 'everyday' draft conditions.

I wonder if anyone can a) recommend a good, inexpensive manometer and/or b) based on either science or experience, suggest a 'favorable' (or average) range of acceptable values (for a wood stove installation) based on manometer readings?

Other than a manual or barometric flue damper, are there any other remedies for an overdraft situation?

Thanks Very Much.

Peter B.

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[ScottF]

Peter , I dont know how pertinent this is to wood burning stoves but here is an exerpt from the coal burning Website. NEPA Crossroads. they say .05 on the water column for an average stove. (see below)

Also here is a website where a person made a simple homemade manometer to test his exhaust. I dont know how you would calibrate it to a standard. He just used it as a comparison.

http://www.ws6.com/mano2.htm

Scott


manometer
From NEPA Crossroads Knowledge Base

A manometer is a gauge to measure the draft present in a stove / chimney installation. The manometer components consist of the indicator box, a fitting installed usually on the flue pipe and tubing connecting them. A fitting for the manometer tube is usually placed through the flue pipe after the exhaust port of the stove and before a barometric damper if present. A tube is installed between this fitting and the manometer device. The tube used at the flue pipe must be able to handle the temperatures present at this location, copper tubing is an example. This high temperature tubing is usually transitioned to the flexible plastic tubing used to connect to the port on the manometer. It can be used to measure the draft and to calibrate / set the counter balance weight on a barometric damper. The draft measurement scale is usually in inches of water. Different stoves recommend different ranges, but generally they are around .05" H2O.

 

[ScottF]

Peter, Here is one that they state is for a multifuel wood furnace for $58.






http://www.yukon-eagle.com/SearchResults/Manometer/tabid/190/Default.aspx

 

[Peter B.]

Maybe a manometer is overkill, I don't know.

Do chimneysweeps / stove installers have other rule of thumb methods for rapidly determining 'Not Enough', 'About Right', 'Too Much' with respect to existing draft given an existing stove / chimney setup?

Thanks.

Peter B.

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[Peter B.]

To put the question yet another way...

If, with a given chimney and stove setup, it is determined that a nominal value of '1' exists for the typical draft conditions, what sort of stove behavior and performance issues might arise if the draft were *twice* the nominal in a setup with otherwise identical conditions?

The point being roughly this... on (professional) installation of a stove, some determination is presumably made whether the chimney (and draft) are actually adequate for the needs of the stove.

Or is this always left to luck?

'Cause of death... curiosity.'

Peter B.

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[oconnor]

Peter, I've wondered the same. My installer ran a 5 inch liner on my Jotul Kennebec, and while it does work, I wonder how well, and if a manometer would allow me to measure how well when compared to the basic setup (the proverbial 15 feet of straight flue of the diameter of the collar on the stove that most manuals describe as a minimum requirement).

I'm sure that the numbers are determined somewhere in the design of the stove. How to get them is another issue.

 

[Peter B.]

Even though I can't claim any knowledge on the subject myself, it doesn't strike me that this would be some sort of 'black art'.

I would think stove manufacturers (nowadays) pretty much *must* have some sort of target draft (manometer) value in mind as a safe average range around which to design a stove's internal flow characteristics.

Hope someone who actually has half a handle on this might chime in.

Thanks.

Peter B.

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[EddyKilowatt]

Nothing magic about a manometer, you just need some metal tubing to connect to your flue, some clear tubing with uniform I.D. in a U shape, and some water. They are on of those fundamental instruments that are kind of self-calibrating... inches of water are inches of water after all. (For our tiny draft levels you might want to incline the U-tube to spread out the readings a bit for legibility).

EPA tests stove according to "Method 28" which specifies a 15-foot flue pipe (half singlewall). My link to the official Method 28 has expired (I looked it up a few years ago), but here's a summary (if the link works):

Method 28

Makes for pretty interesting reading... they test our stoves using air-dry 2x4s and 4x4s!



Here's one of the EPA pages pertaining to wood heat, including a link to the applicable regulation... though all it does is reference "Method 28", which is a lot harder to find!

Wood Heater Regulations

I think John Gulland speaks in terms of draft measurements, perhaps you could contact him to find out 'typical' levels.

Eddy

 

[Peter B.]

Thanks to all who have replied, but...

Actually, though all my questions might be poorly stated or phrased, I'm not (so much) interested in theory as in immediate practical application.

If presented with a 'suspected' overdraft situation, how might it be diagnosed as such... and how might it be corrected?

Isn't there any specific x value or rule of thumb as a starting point that indicates nominally adequate, inadequate or definitely over draft conditions?

*Even knowing* that same conditions can be variable under different circumstances?

Still trying to get a handle...

Peter B.

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[EddyKilowatt]

Florida Bungalow Syndrome (though Californians cause it too.)

 

[ScottF]

Eddy, Good article. I find the maual flue damper works well for me in my situation. I have an old stove that would easily overdraft without one. My flue damper is easily accessible from inside the stove (short flue pipe) so it is easy to keep clean. An old leaky stove makes it the only control of the draft and the fire. Thanks for the article.

 

[CrappieKeith]

Even though I can't claim any knowledge on the subject myself, it doesn't strike me that this would be some sort of 'black art'.

I would think stove manufacturers (nowadays) pretty much *must* have some sort of target draft (manometer) value in mind as a safe average range around which to design a stove's internal flow characteristics.

Hope someone who actually has half a handle on this might chime in.

Thanks.

Peter B.

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Draft speeds in most chimneys might normally be in the .08" range. Wood does not need to burn that fast to make all of the btu's available.
Flue gas temps need to be over 300 degrees to stay away from condensing.
So if you set it at .04"WC the flue gas temps should run right around 400 degrees which is a great target number to hit.
I've seen some manufactures say .04-.06 is the range.
Oh....get a manometer.

 

[Peter B.]

Keith:

Thanks for 'the numbers'... now maybe I have reason to buy a manometer.

(I'd almost forgotten this thread... I should go and reread the linked articles above too.)

Peter B.

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[CrappieKeith]

I see people with stack thermometers taking flue temps.This means nothing since all of the heat travels up the center of the flue.
A manometer is the only real way of measureing and setting draft speeds ie...stack temps.

 

[kgrant]

In my Blaze King manual it says:

CHIMNEY DRAFTS
If you suspect a draft problem in an existing chimney, determine the draft by using a water manometer (draft gauge).
The draft should be measured with the stove at medium burn. After the measurement is completed, fill any holes that
were made in the chimney connector by using a sheet metal screw of proper size. The draft should measure .02" or
above. Drafts below .02" will cause excessive smoke spillage, incomplete combustion and fire start-up problems.



I couldn't find anywhere in the manual where they talk about how to diagnose/solve an overdraft problem.

 

[Peter B.]

kgrant:

Thanks... even better... the numbers are now getting bracketed.

From a possibly problematic low of .02" to a nominal high of .08"... with .04-.06" perhaps in an 'ideal' range.

I'm surprised there's not more attention paid to this here with the wood burning crowd. Coal burners are pretty careful about the actual chimney draft... and correct for it by various means.

There are a lot of posts here on both sides of the 'fence' - fairly obvious underdraft or overdraft problems - but they tend to be by description only (e.g. my stove smokes, my stove won't hold a fire longer than 2-3 hours)... anecdotal, rather than scienterrific.

Maybe it's too often overlooked.

--

CrappieKeith:

I maintain that flue temps definitely have a <relative> utility, even if not <absolutely> accurate.

Anyways...

Peter B.

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[RonB]

Peter,
I would be hesitant to generalize that last .02" reference number and apply it to your situation. Likely, Blaze King determined that number through tests on a specific model stove/design and with a given flue size and height. Do you have a particular problem with your stove related to draft? Retrofitting a display window in your stove would give you all the info you needed (by reading the flame/combustion visually) to set the correct draft for your stove on any given day.

 

[CrappieKeith]

Sure enough Peter....I just see too many folks trying to eyeball or guess which normally results in operations that they do not like ie....excessive creosote or short burn times with too much heat in the home.

 

[kgrant]

When I first installed my blaze king, I was having trouble with smoke spillage during loading/startup. I went down the the store to get some more stove pipe to extend my chimney. I asked the gentleman I bought my stove from about draft and manometer readings, he didn't have a clue what I was talking about. I didn't push the issue though. I'm sure someone at the store (an installer) would have known more, but I thought the salesman should have known something about it.

I would say the ideal draft would be just enough to not allow smoke spillage, which would be different for different style stoves. Would there be any advantage to having more draft than that?

 

[Peter B.]

I think (for me) the question first came up last year when I tried to burn coal. My draft has always been adequate for wood, but I couldn't seem to keep a coal fire burning... and the draft became a question mark (though there were other unanswered questions with respect as well, including grate configuration and square area... and operator (in)competence.)

I had just never seen (even) a range of acceptable manometer readings for wood stove operation before... and curiosity often gets the best of me.

Next year, I hope to better equip myself... with a manometer or draft gauge, an IR thermometer and some additional cheapie probes...

I'm not making it a full time 'study', but I sure do enjoy observing and speculating.

Thanks to all who've replied.

Peter B.

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[kgrant]

When I first installed my blaze king, I was having trouble with smoke spillage during loading/startup. I went down the the store to get some more stove pipe to extend my chimney. I asked the gentleman I bought my stove from about draft and manometer readings, he didn't have a clue what I was talking about. I didn't push the issue though. I'm sure someone at the store (an installer) would have known more, but I thought the salesman should have known something about it.

I would say the ideal draft would be just enough to not allow smoke spillage, which would be different for different style stoves. Would there be any advantage to having more draft than that?

yes! butt 4 coal get a co detector & i bet u wont need it

Won't need what?

 

[snowtime]

I have a different take on draft. I think it advantageous to have a strong draft with a damper. I say this because if you ever have any serious wind a weak or just sufficient draft will backdraft [smoke you out] way before a strong draft will. You just leave the damper all the way open when its blowing hard. Also starting from a cold start is a breeze as is shoulder season which can be a pain with a weak or "just enough" draft. A damper also adds the ability to control those supper high draft times like when its -40 out. I have had marginal drafts in the past and will not ever do that again.

 

[Peter B.]

Readily agreed as to preference for a stronger draft... opposed to smoke spillage.

Same balance tends to be a tightrope here too, but I've had no wind induced backdrafts with my current setup for... ever. My luck.

(I do, however, have memories of such... and the aggravation involved. Added insulated chimney length and/or a draft inducing / wind defeating chimney cap might be in order.)

I have a manual flue damper and rely on it for 'control'... and wouldn't be without it. I just sometimes wish there was a more elegant way to provide (semi-auto) overdraft control. From what I understand, barometric dampers are NOT a good idea for a wood burning application because of the 'uncontrolled-added-air-to-chimney-fire' syndrome... but I'd like to imagine a decently implemented bimetal spring flue damper control might be possible... either 'close-coupled' with the stove outlet flange... or further up the flue.

Just thinkin' out loud...

Peter B.

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[CrappieKeith]

When I first installed my blaze king, I was having trouble with smoke spillage during loading/startup. I went down the the store to get some more stove pipe to extend my chimney. I asked the gentleman I bought my stove from about draft and manometer readings, he didn't have a clue what I was talking about. I didn't push the issue though. I'm sure someone at the store (an installer) would have known more, but I thought the salesman should have known something about it.

I would say the ideal draft would be just enough to not allow smoke spillage, which would be different for different style stoves. Would there be any advantage to having more draft than that?

Having a good draft is key to a clean flue and no smoke in the house.
Besides lengthening a flue make up air needs to be available.You can make a vacuum in the home without it.