Flue diameter - can I get away with an inch less than reccommended?

[jonperry64]

Hi there
I have a Jotul3 CB which requires a 6 inch flue. I also have several meters of (very expensive) five inch twin wall flue. If I were to use this flue what would happen? Would it be dangerous? I will be installing the stove in an out building where there is no chimney - hence the need for twin wall. Many thanks.

 

[precaud]

My guess is, with a 3CB you'd probably be fine with a 5 incher. Just make sure it's tall enough. I'll soon be installing my F602 in the basement, coupled to a 5" rigid liner. But... the 602 has a 5 inch flue connector and comes with an adapter for 6" pipe...

 

[jonperry64]

Many thanks. Anyone else have a view on this?

 

[webbie]

Where are you located? 5 inch is not available generally in the USA.

I would concur with the opinion that a chimney of that size of adequate height - say at least 16 feet - and straight up if possible, would work well for that particular stove. As mentioned, many of the European Jotul, Lange, Morso and other models originally came with metric flues that were about 4.9 equiv.

 

[jonperry64]

Thanks Craig - this is reassuring and means that hopefully I won't have to buy another load of twin wall flue. Presumably adapters are available to link the 6 inch stove outlet with the 5 inch flue? I'm based in the UK by the way. Very informative site. Cheers

 

[webbie]

Yes, adapters are available. In fact, it used to be that even Jotuls in the USA came with the smaller flue (4.9) and had a cast or sheet metal adapter included. Way back when, they didn't even have the adapter! (we had to do a super-crimp on 5" pipe or adapter to make 'em fit).

BTW, the same size flue was on even large Surdiac and Efel coal stoves.

Actually, truth be told, certain stoves like the 602 would have (and maybe still would) work BETTER with the smaller flue. But since pipe is usually only available in certain sizes (6 and 8, for instance, in the USA), most stove companies choose one or the other.

 

[precaud]

Agreed. Over the years, I've used 602's (old and new) on both 5" and 6" flues and I prefer the fiver, the main difference being better control (i.e. a more consistent draw) at lower burn rates.

 

[struggle]

I have a Hearthstone Mansfield and it runs on a 5.5" stainless flex liner and it actually seems to overdraft it. Chimney length is 24' long.

It works very well so far for a large stove.

 

[Todd]

22 ft 5.5" liner drafts great for me to.

 

[BrotherBart]

I burn an F3CB into a 30+ foot 5.5 liner and it drafts like a vacuum cleaner was attached to the top of the chimney. In fact I am preparing to replace the six inch smoothwall liner in my other flue with a 5.5.

 

[jonperry64]

Thanks all for your replies. I think my question has been answered 'good and proper'.

 

[begreen]

jon, will you be taking the flue from the top or the rear of the stove? With top exit, and say 6 meters of straight flue (no elbows), the stove should work well. However, if rear exit into 2-3 elbows on a 4 meter flue, I would not be surprised to get some smoke when opening the door on milder days, especially if there is low pressure weather.

 

[elkimmeg]

Jon nobody here can answer you question all they can do is guess The person you should be direction this question to is your inspector it is his signature that you will be required to c for compliance. If your manual does not list being tested for that pipe diameter then how would you expect your inspector to acccept a 30% area reduction.

30% is quite a difference, not just a few decimals, but a considerablee difference.. How would you like for your stove to under preform 30% from the get go. There is a good chance this could happen Nobody here can say for sure even the manufacturer can't once the stove is tested and approved. As an inspector I would have a real hard time without proof of testing accepting any setup reduced 30+ % How effecient can it be when its exhaust path is reduced that much? Testing by the manufacturer can establish that but nobody here is an expert and can tell you your answer

 

[begreen]

Agreed we are not expert on the level of the manufacturer, but the manufacturer is unlikely to have this data or offer it. I burned this stove a year in a similar climate and our stove had a rear exit, one elbow, going to a 16 ft stack. Once hot, we ran it with the draft damper mostly closed. Much less than a 30% reduction and it was fine. Stack stayed very clean and stove drafted well. I think it's safe to say that with a straight up stack of sufficient height, top exit, the stove will work ok. It may be a little balky under that conditions mentioned, but once going, it should be fine.

 

[jonperry64]

Interesting to get another perspective - and I take your point. Fortunately I can choose whether to use the top or rear exit. On the basis of the advice I have received here I will take the flue out of the top and straight up with no angles or bends. I will only be able to use 4 meters comfortably - as two of these would protrude above the roof and I don't think you are supposed to have more than 2 meters 'unsupported' flue above the roofline. I'll let you know how it goes.

 

[precaud]

Jon nobody here can answer you question all they can do is guess

Yes, but it's not an uninformed guess.

The person you should be direction this question to is your inspector it is his signature that you will be required to c for compliance.

Or - do the installation well and don't bother showing it to him...

30% is quite a difference, not just a few decimals, but a considerablee difference.. How would you like for your stove to under preform 30% from the get go. There is a good chance this could happen

Oh Elk, there you go again... No, there's almost NO chance that could happen - this is typical Elk scare tactics, resorting to the part of his brain that parrots code instead of using reason and intuition. From the same stove, compared to a 6", gasses in a 5" flue will run hotter and faster, both of which are a good thing for draft... which I'd say would be beneficial for a 4-meter chimney, which is borderline.

 

[webbie]

RE: Just a guess

Of course it is a guess. An informed guess. If every single situation was covered by code or owners manuals, no common sense or experience would be required. In fact, we would not need to have this site or forum. I knew a very successful inspector who used to swap links with our site - his site was called "Code Check" and his job was simply to check codes on anything. He ended up writing some successful books on the subject...
http://www.codecheck.com/

FYI, even the larger Jotul 118 , with a 24" log and vastly larger firebox, used a flue size of 4.9".

Here is a typical spec sheet on Lange stoves....another stove with a vastly larger firebox (26 inch log):

https://www.hearth.com/econtent/index.php/wiki/File:langspecs.JPG/

I also sold other brands of stoves with a 5", including Ulefos (Made by Dovre).....

In fact, the only European stoves which had larger flues were those that had vastly oversized door opening, like the Jotul Fireplaces. In that case, the flue size was needed to make certain that smoke did not leak out the door when loading.

Obviously, an opinion from afar is just that. If you want to make 100% certain, ask a local stove shop or installer, or your code official (if you have the same type there, and if he is versed in solid fuel). It may be that the sweep or another tradesman in the UK is more experienced.

Here is a bit more guesses just to clarify:

The first concern of chimney sizing is the capacity of the chimney. I sold HS TARM boilers which had a 6" flue (actually a bit smaller) with the total BTU input being as much as 250,000 BTU per hour. Chimney capacity is large a function of chimney diameter AND height. That is why you need a decent chimney - 16-20 feet or more above the stove and straight up would be best.

A stove like the Jotul 3CB operates at a max. of 42,000 BTU.....and mostly operates in the range of 15 to 30K BTU per hour. This is well within the capacity of that chimney.

The second concern is whether the stove will tend to smoke when the loading door is opened. As a for instance, a large American Stove - the Defiant Encore - was sold with only an 8" flue for many years. But then the manufacturers started offering a 6". with the caveat that it could not be used with the (giant) double front doors open. In other words, it was enough draw to vent that medium-large firebox and all the heat, but not to sweep smoke out the smoke when the front doors were open.

The Jotul #3 had a rather small door opening, because even though the door is of medium size, when you open it there is an ash retainer along the bottom and air input channel across the top. It will be the chimney height (and lack of turns) that determines whether or not any smoke leaks when loading....the taller the better.

As far as stove performance, I see no effect at all when the unit is closed. Basically, if the unit draws and keeps the smoke from rolling out when loading, it should work as good or better than as with a 6,7, or 8

That's my story and I am sticking to it....

 

[begreen]

Agreed, for the record 6" -> 5" is a <17% reduction.

Let us know how it works out Jon. The 3CB is a nice little stove. I think you'll like it.

 

[elkimmeg]

Agreed, for the record 6" -> 5" is a <17% reduction.

Let us know how it works out Jon. The 3CB is a nice little stove. I think you'll like it.

Your math is ok but you forgot to multiply the area by pie r squared. The diffencce in a crossectional are is app 19.5" for 5" pipe and 28.25" for 6" pipe. When I do the math that eequates to about 30%

I read the manual and cut and pasted the pertinent info concerning this situation Just wondering how else one interpets the question at hand without tested results.

My suggestion is to purchase a stove that will work with the currrent chimney. If the poster were not concerned he would not have asked the question The manual he has outlines the proper installation chimney needed. I think he asked the question to justify not being listing or code compliant. Fact insalling that stove in a 5" chimney does to things that are true it will not be code compliant and it will not be listing compliant. Anyone else that makes compromise suggestions please use acepted testing data or refference code language to support your arguement.

Tell someone that you scoffed the code and made it work is not scientific or really the intellegent aproach on a public forum. Telling me about a stove from way back yesteryear ,Lang that is noway indicitive of EPA phase II moderns stoves, again does not apply and is bad science, We all know how draft sensitive EPA stoves are and there is no comparison to 30 year old stoves and modern technology


Direct cut and past from the manual

Safety notice: If this solid fuel room heater is not properly installed, a house fire may result. For your
safety, follow the installation directions. Contact local building or fire officials about restrictions and installation inspection requirements in your area. Save these instructions for future reference. Page 2

,
Check Building Codes
When installing, operating and maintaining your Jøtul
F 3 woodstove, follow the guidelines presented in these
instructions, and make them available to anyone using or
servicing the stove.
Your city, town, county or province may require a building
permit to install a solid fuel burning appliance.

In the U.S., the National Fire Protection Association’s Code,
NFPA 211, Standards for Chimneys, Fireplaces, Vents and
Solid Fuel Burning Appliances, or similar regulations, may
apply to the installation of a solid fuel burning appliance in your area. Page 3

Stove pipe - chimney connector
The chimney connector is a single walled pipe used
to connect the stove to the chimney. For use with the
Jøtul F3 the chimney connector must be 6” in diameter,
with a minimum thickness of 24 gauge black steel. Page 4

The chimney size should not be less than the cross-
sectional area of the flue collar, and not more than three
times greater than the cross-sectional area of the flue
collar.

Page 6

Is there another set of standards that have exceptions that I am unaware of? Seems pretty clear cut what is required.

Even bettter who here has done the testing and can certify a 30% reduction reconized by UL I know I can't

I thought The Hearth was about getting it right,correct installation practices. It pains me to be sourounded by so many experts yahoos that have not one shread of documentation to back them up

And when I back it Up they are telling you I'm wrong?

The only correct answer is in your manual

 

[begreen]

I stand corrected on the sq in.. But still think that the stove with 13' straight up pipe of 5" will work at least as well as a stove with 13' of 6" pipe with 2 elbows. Will it smoke a bit when the door is opened under the conditions mentioned? Yes. Will it draft poorly when starting up from cold under said conditions? Very possibly. Am I recommending this install no, just answering the question. Will it work, yes with stated caveats. Would I do it this way? No, given the short length of stack.

Elk, have you ever used a non-standard adapter on a woodstove? Was it in violation of the stove mfg recommendations?

 

[elkimmeg]

Elk, have you ever used a non-standard adapter on a woodstove? Was it in violation of the stove mfg recommendations?

Yes I used an off set box you are right it was non standard made of 12 ga steel not like those chincy homesavor ones of 24 gage

In code there is equilvqancy the cross secctiona; area of the offfset was far greater than required plus 5/8 of inlet and outlet holes over lapped ant to deflecct the smoke path I installed angle baflet in side the conversion box There are none in the homesaver setup. I custom made the box long before Homesaver offered an ofset box.

There is no code in connector pipe that says 12 gage material in not accepted there was no language concerning offset boxes in the installational manual the only language that remotely applied was not to reduce the cross- sectional area which I did not do. I did post a picture of if before I got rid of it. New stove did not need the offfset box it was higher and with adjustiable leg screws a perfic match with greater than 1/4 pitch.


In masonry chimney code there is a parbolic curb graft part of the premise is the relationship of the fue diameter is connected to height meaning a taller chimney may get by using a smaller clay flue liner Example the 8/12 clay flue may not meet the draft requirements of the fire place opening at a 24' height but using the curb graft it might become accceptiable at 30'

I wish language would require a draft test first prior to installations. Boy would that solve a lot of installation problems. As it is, we are all installing appliances/wood/coal stoves in unknown conditions If the manufacturer gave draft requirement in terms of WC and the flues were tested in WC ( water collum WC) situations like this could get resolved.'
Thinking outside the box a bit here A chimney run of required verticle height is effected by offsets elbows They are allowed providing Verticle length is 5' more for eash 90 degreee offset.

Think in terms of lenght what if the lack of diameter was made up with 30% higher verticle length Equvalancy?

I can't believe I going back to work man is it hot Mixed .. 12 bags of concrete this morning the last of the footings are poured. I should post what I accomplished yesterday first day doing actuall carpentry work and I completed the 12/16 deck for the 3 season room I building IT was a lot cooler yesterday..

 

[webbie]

Elk, once again you are NOT thinking outside the box and simply pointing to Black/White Yes/NO.

I always have said that if you ask the government, the answer is always NO (it's easier), and you prove the point.

There is no problem for you to make your usual post concerning your concerns or advice. But I certainly don't want every thread becoming a teat for tat calling your fellow board members Yahoos or calling them out.

What if you find out all the Hardie board installations you suggested were wrong (in violation)? Are you going to go rip it all out and inform the customers?

Large numbers of people here and in the field have 5.5" flex kits, which as you know are corrugated - meaning that they are the equiv of 5". Get a small layer of soot in them and they are even worse.

Let's stop all the "chest beating" and "name calling" and since the UK is not in your jurisdiction or mine, give your opinion and leave it at that. If you really think that your experience and opinion are that much more valuable than everyone else here, I will help you (no kidding) start a board or blog in which the questions are asked to...and answered by you. But this place is not that. Please - the season is starting and I do not want to have to babysit the board. Give your opinion, and let everyone else give theirs. We ALL know what the manual says (actually, I have no idea what the UK manual says). We also have no idea of UK guidelines nor practices.

We do not publish this board as an "information service" such as the Dictionary or NFPA. We publish it specifically because most situations DO vary from one to another. If that makes us Yahoos...well, YAHOO!

 

[elkimmeg]

Since I have acetylene torches here I exposed hardi backer board to extreme heat enough to melt and cut steel If I go to the gathering I can bring a sample and the torches so that all ccan witness what extreme conditions Hardibacker boadr can withstand I don't give a ---- if anyone buys the product. For that matter cement board is not listed by the manufacturer for hearth extentions either It is basically listed for tile backer it does not even give tinsel strenght.

I was unable to ignite the hardi backer board thought it did blacken it a bit..

I don't get it ,provided the supporting information that backs my point and you are calling that wrong?
I did noting more than produce manufactures specs, that have been tested and approved, anyone here could have looked up and produced
You would rather use hearesay and unsubstiantiated guesses? I can't believe you are trying to win that arguement when there is insurmountable evidence to support my point and you are using heresay? Am I in the wrong forum I thought stoves were to be installed to listing standards and not made up to suit ones needs Or is it convient I like this requirement but I don't like that one, My first response was to ask the code official in his jusisdiction we here cannot advise of less than manufactures spect of the listing I can't you can't but that does not stop many from making non compliant suggestions.

Craig you might as well permantely ban me. I will not stop promoting safe installation code compliant practices. That way there you do not have to babysit factual substiantiated post.

No one else provided tested proof that reduction of 30% is acceptable NFPA 211 has language forbidding reductions The International Mechanical code has the same language and the manufactur's listing has the same language. Then my math was questioned but later confirmed. I proved and backed up every statement something no one else did and I'm wrong?

what a twisted way of looking at things you are right I don't belong here. I might say something factual that someone does noty want to hear and chase them away I statrting to get it forgrt what is right and factual just tell them what they want to hear Too bad its not part of my makeup IT is better to bs them and have them stay arounfd who cares if the information is wrong and could compromise their safety. Come to think of it you just provided the very reason for my profession. I never expected this post to provoke an arguement I was hoping once the evidence was presented it would be over I asked for the sourses where exceptions were listed but nobody provided any.

Craig you are right to voice concerns about corrigated liner friction, NFPA 211 says the shall be oversized 20% to make up for increased friction. Glad you pointed it out and brought to the attention of viewers and other members

So some heartth member has a mayonaise jar stored on funken wagnel's porch from noon today and has the answer. Are all other hearth members almighty Carnac and the information in the mayonaise jar is all knowing and proves all codes and manufacture listing wrong?

 

[webbie]

OK, we will use the Elk Mapp torch test from now on for before we Yahoos spout our opinions!

Conversation overheard:

"Is it UL tested?"
"No, but it is Elk Mapp Approved".

or
"Can I close off 1" of my flue"
"Craig says it should be OK, and he slept at a Holiday Inn Express last night".

As far as pontification, if you (ELK) can prove to me that you know UK codes, manuals and practices any more than we do, I will stand corrected. Nothing wrong with giving your opinion (I repeat), but it is simply that - your opinion. Your badge does not cross the atlantic, and possibly not even state lines...and, even if it did, you feel free using your own "mapp gas" tests, well...just the same, we Yahoos feel free using "we did it 100 times and it works fine" tests.

Listen, any more Krap from you and I'm putting a Volgelzang link in my signature....just imagine that!
:coolgrin:

 

[elkimmeg]

Non-Combustibility
HardieBacker™ cement board is recognized for use in non-combustible construction in NER-405.

Surface Burning Characteristics
When tested in accordance with ASTM test method E-84:
Flame Spread
Fuel Contributed
Smoke Developed 0
0
5

Thermal Resistance
(Approximate value) 1/4'' thick: R:0.13

Again yo asked for supporting information and facts.. I Challange you to prove where one can Refute all known code bases and manufacture tested listings I want proof you asked me to provide so I'm asking you to support your point with proof

BTW I am Nationally Certified that means since all states adopted the international code I can be hired in all 50 states The mass qualifications are that I pass the national battery of testing which I will find and scan proof of passage in 1997

British Standards and Codes of Practice, particularly BS6461,
CP403 and BS5449, relating to the installation of solid fuel appliances.


http://www.jotuluk.com/content/products/ProductArticle____3619.aspx

Installation of a fireplace must be according to local codes and
regulations in each country.
All local regulations, including those which refer to national
and European standards, must be observed when installing the
product.
Both an installation manual with technical data and a manual
on general use and maintenance are enclosed with the product.
The installation can only be used after it has been inspected by a qualified inspector.

3.4 Chimneys and flue pipes
A chimney can be linked to the fireplace and flue approved
for solid fuel-fired fireplaces with a flue gas temperature as
specified in «2.0 Technical data».
The cross-section of the chimney must be at least equal to
the cross-section of the flue. Please use «2.0 Technical data» •

I may not have jusisdiction in UK but I still can read their installation manual to see the correct way to do it