Which chimney to choose: we understand the types and their features

Think­ing about build­ing a chim­ney in your home? Before get­ting down to busi­ness, let’s fig­ure out how to cor­rect­ly design and mount it.

All about chimneys

Chim­ney Require­ments

Kinds:

  • Brick chim­ney
  • Steel chim­ney
  • Pipes-“sandwiches”
  • Ceram­ic chim­neys

Chim­neys and fire­places

Is it pos­si­ble to con­nect two pipes to the chim­ney

How to improve trac­tion

In which pipes does con­den­sate form?

General requirements for chimneys

Fire­place inserts can be con­nect­ed to an exist­ing chim­ney, but in this case the choice of fire­box pow­er is dic­tat­ed by the cross-sec­tion­al area of ​​the smoke chan­nel. Gen­er­al require­ments for chim­neys are con­tained in SNiP 41–01-2003 “Heat­ing, ven­ti­la­tion and air con­di­tion­ing”. This reg­u­la­to­ry doc­u­ment allows the use of chim­neys made of dou­ble-walled steel pipes with ther­mal insu­la­tion made of non-com­bustible mate­r­i­al (at a flue gas tem­per­a­ture of not more than 500 ° C) and the instal­la­tion of umbrel­las, deflec­tors and oth­er noz­zles on chim­neys, if these devices do not pre­vent the free exit of smoke (in this its dif­fer­ence from SNiP 2.04.05–91).

The height of the chim­neys from the mouth to the grate must be at least 5 m. The height of the parts of the pipes ris­ing above the roof is at least 0.5 m above the flat roof, as well as above the ridge or para­pet at a dis­tance of no more than 1.5 m; not low­er than the ridge or para­pet at a dis­tance of 1.5–3 m to them; not low­er than a line drawn from the ridge down at an angle of 10 to the hori­zon, with a dis­tance of more than 3 m between the pipe and the ridge.

Pipe bends are allowed at an angle of up to 30 to the ver­ti­cal at a dis­tance of no more than 1 m. Pipes on build­ings with roofs made of com­bustible mate­ri­als should be equipped with spark arresters made of met­al mesh with holes no larg­er than 5 g 5 mm. The dis­tance from the out­er sur­faces of brick or con­crete chim­neys to rafters, bat­tens and oth­er roof parts made of com­bustible mate­ri­als must be at least 130 mm; from ceram­ic pipes with­out insu­la­tion — 250 mm, with insu­la­tion — 130 mm. As for walls and floor ele­ments made of com­bustible mate­ri­als, the dis­tance from the inner wall of the smoke chan­nel is nor­mal­ized here: 500 mm to unpro­tect­ed struc­tures and 380 mm to pro­tect­ed ones.

How­ev­er, the appen­dix to SNiP oper­ates with the term “cut­ting”, that is, we are talk­ing about a brick pipe. There are no clear rules for mod­ern mod­u­lar sys­tems, and devel­op­ers usu­al­ly fol­low the man­u­fac­tur­er’s instruc­tions.

Types of chimneys

Brick chimney

Until recent­ly, brick chim­neys, both in urban and rur­al con­struc­tion, were prac­ti­cal­ly uncon­test­ed. Being a uni­ver­sal struc­tur­al mate­r­i­al, brick allows you to vary the num­ber of chim­ney chan­nels and wall thick­ness (you can make the nec­es­sary thick­en­ings in the places where floors, roofs pass, as well as dur­ing the con­struc­tion of the out­door part of the chim­ney).

With the obser­vance of build­ing tech­nolo­gies, a brick chim­ney is very durable. How­ev­er, it also has dis­ad­van­tages. Due to the sig­nif­i­cant mass (a pipe with a cross sec­tion of 260 130 mm and a height of 5 m, laid out in half a brick, weighs about 1.5 tons), it is nec­es­sary to arrange a foun­da­tion. And for the con­struc­tion of all this struc­ture will require a lot of time and effort. The cross sec­tion of the chan­nel (rec­tan­gu­lar or square) is not opti­mal for trac­tion. In addi­tion, with peri­od­ic use in the cold sea­son, the ser­vice life of a brick pipe is great­ly reduced due to the aggres­sive effects of con­den­sate.

For the device of a brick chim­ney, a very high qual­i­fi­ca­tion of builders is nec­es­sary.

Common building mistakes

  • The choice of low-qual­i­ty or unsuit­able bricks (weak­ly burned par­ti­tion or wall).
  • The thick­ness of mason­ry joints is more than 5 mm.
  • Lay­ing on edge; the use of stepped (“toothed”) mason­ry on inclined sec­tions.
  • Incor­rect prepa­ra­tion of the solu­tion (for exam­ple, if the ratio of parts of clay and sand is cho­sen with­out tak­ing into account the fat con­tent of clay), inac­cu­rate split­ting or cut­ting of bricks.
  • Inat­ten­tive fill­ing and dress­ing of mason­ry joints (the pres­ence of voids and dou­ble ver­ti­cal joints).

Lay­ing pipes close to struc­tures made of com­bustible mate­ri­als. The con­di­tion of the brick pipe requires con­stant mon­i­tor­ing. Pre­vi­ous­ly, it was cer­tain­ly white­washed, since it is eas­i­er to notice soot on a white sur­face, indi­cat­ing the pres­ence of cracks.

Steel chimney

Stain­less steel pipes can be safe­ly attrib­uted to the most wide­ly used type of chim­ney today. Steel mod­u­lar sys­tems have a num­ber of unde­ni­able advan­tages. The main ones are low weight, ease of instal­la­tion, a wide selec­tion of pipes of dif­fer­ent diam­e­ters and lengths, as well as shaped ele­ments. Steel chim­neys are made in two ver­sions — sin­gle- and dou­ble-cir­cuit (the lat­ter is in the form of a “sand­wich” of two coax­i­al pipes with a lay­er of non-com­bustible ther­mal insu­la­tion).

The first ones are designed for instal­la­tion in heat­ed rooms, con­nect­ing a fire­place to an exist­ing chim­ney, as well as san­i­tiz­ing old brick pipes. The lat­ter are a ready-made design solu­tion that is equal­ly suit­able for installing a chim­ney both inside the build­ing and out­side. A spe­cial type of smoke chan­nels made of stain­less steel are flex­i­ble sin­gle- and dou­ble-walled (with­out ther­mal insu­la­tion) cor­ru­gat­ed sleeves.

For the pro­duc­tion of sin­gle-cir­cuit chim­neys and inner pipes of “sand­wich” type chim­neys, alloyed heat- and acid-resis­tant sheet steel (usu­al­ly 0.5–0.6 mm thick) is used. Sin­gle-cir­cuit chim­neys made of car­bon steel, coat­ed on the out­side and inside with a spe­cial black enam­el, even sur­pass stain­less steel pipes in heat resis­tance; they are also not afraid of con­den­sate, but only if the coat­ing is intact, which is easy to dam­age (say, when clean­ing the chim­ney). The ser­vice life of uncoat­ed pipes made of “black” steel with a thick­ness of 1 mm does not exceed 5 years.

Pipes-“sandwiches”

The cas­ing (shell) of “sand­wich” pipes, as a rule, is made of ordi­nary (non-heat-resis­tant) stain­less steel, which is elec­tro­chem­i­cal­ly pol­ished to a mir­ror fin­ish, and some man­u­fac­tur­ers offer enam­el paint­ing in any col­or accord­ing to the RAL scale. The use of a gal­va­nized steel cas­ing is jus­ti­fied only when installing a chim­ney inside the build­ing. Out­side, such a pipe, if the chim­ney is active­ly used, will not last long: due to peri­od­ic heat­ing, cor­ro­sion inten­si­fies.

The lay­er of ther­mal insu­la­tion in “sand­wich” pipes solves three prob­lems at once: it pre­vents over­cool­ing of flue gas­es that neg­a­tive­ly affects draft, does not allow the tem­per­a­ture of the inner walls of the chim­ney to drop to the dew point, and, final­ly, pro­vides a fire­proof tem­per­a­ture of the out­er walls.

The choice of insu­lat­ing mate­ri­als is small: usu­al­ly it is wool — basalt (or organosil­i­con, per­lite sand (but it can only be cov­ered dur­ing the instal­la­tion of the chim­ney).

Such a very impor­tant char­ac­ter­is­tic of the chim­ney as gas tight­ness depends on the design of the pipe joints, so each man­u­fac­tur­er strives to bring it to per­fec­tion. Thus, the seal­ing of some chim­neys is pro­vid­ed by cen­ter­ing cou­plings; a dou­ble annu­lar pro­tru­sion formed at the junc­tion is crimped by the clamps includ­ed in the deliv­ery of each mod­ule. In oth­er chim­neys, a cone-shaped con­nec­tion is pro­vid­ed in com­bi­na­tion with an annu­lar ledge.

The vast major­i­ty of stain­less steel chim­neys are mount­ed in the tra­di­tion­al way, and much depends on the qual­i­ty of the parts. Usu­al­ly, the upper mod­ule is put on the low­er one, how­ev­er, sin­gle-cir­cuit ones, and for exter­nal lay­ing, the dou­ble-cir­cuit mod­ules should be joined, insert­ing the upper one into the low­er one, which will avoid con­den­sate leak­age through the joints.

Ceramic chimneys

Ceram­ic chim­neys are the same “sand­wich­es”, but “cooked” accord­ing to a com­plete­ly dif­fer­ent recipe. The inner tube is a pot­tery made of fire­clay mass, the mid­dle lay­er is unchanged basalt wool, the out­er one is sec­tions of light­weight con­crete or mir­ror stain­less steel.

Ceram­ic chim­neys are resis­tant to high tem­per­a­tures (up to 1000 °C), con­den­sate and at the same time have the main advan­tage of mod­u­lar sys­tems — they can be quick­ly and eas­i­ly assem­bled.

There are ceram­ic sys­tems and their dis­ad­van­tages. Chim­neys with a cas­ing made of con­crete have a sig­nif­i­cant mass (1 lin­ear meter weighs from 80 kg), can only be used as indige­nous (free-stand­ing), do not allow to bypass obsta­cles. The “weak link” of such chim­neys is the con­nec­tion node. Man­u­fac­tur­ers pro­vide for the use of a met­al mod­ule (mod­ules), which has a short­er ser­vice life and there­fore will require replace­ment in the future, which must be tak­en into account when build­ing a fire­place.

And final­ly, the met­al does not go well with ceram­ics, since it has a high coef­fi­cient of ther­mal expan­sion: along the perime­ter of the steel pipe, where it enters the ceram­ic, it is nec­es­sary to leave a rather large (about 10 mm) gap, which is filled with asbestos cord or heat-resis­tant sealant.

How­ev­er, the high reli­a­bil­i­ty and dura­bil­i­ty of ceram­ic chim­neys (the fac­to­ry war­ran­ty is 30 years, and the actu­al ser­vice life, accord­ing to man­u­fac­tur­ers, is more than 100 years) make it pos­si­ble to turn a blind eye to the list­ed short­com­ings.

What pipes are suitable for fireplaces

The degree of reli­a­bil­i­ty and effi­cien­cy of chim­neys large­ly depends on the heat­ing devices con­nect­ed to them, and vice ver­sa. There­fore, for each type of fire­places, there is an opti­mal chim­ney option.

The use of ther­mal­ly insu­lat­ed mod­ules along the entire length of the chim­ney (start­ing from the fire­box) is jus­ti­fied in those rooms where the fire­place per­forms main­ly dec­o­ra­tive func­tions. Usu­al­ly, in order to use the heat of the exhaust gas­es, the first 1.5–2 m of the chim­ney is col­lect­ed from sin­gle-wall pipes in com­pli­ance with the nec­es­sary fire safe­ty mea­sures.

The fol­low­ing require­ments are imposed on the chim­ney of a clas­sic mason­ry fire­place with an open fire­box: its chan­nel can only be straight-through, with a cross sec­tion of at least 1/10 of the cross sec­tion of the fur­nace open­ing. “Island” fire­place), they are equipped with a smoke hood that pass­es into the chim­ney. The lat­ter should have an increased cross sec­tion, and quite often it is also equipped with an exhaust device (smoke exhauster).

Closed hearth fire­places are the most com­mon today. Their fun­da­men­tal dif­fer­ence from the clas­si­cal ones is that the air nec­es­sary for com­bus­tion does not enter through the fur­nace open­ing, but through the blow­er, and by manip­u­lat­ing the dampers, you reg­u­late the inten­si­ty of com­bus­tion. The vast major­i­ty of fire­place inserts can be equipped with a stain­less steel mod­u­lar chim­ney.

And final­ly, the last type is the fire­place stove. The main dis­tin­guish­ing fea­ture of such devices, which makes them look like a real stove, is the pres­ence of a built-in smoke chan­nel, pass­ing through which the flue gas­es are cooled to a fair­ly low tem­per­a­ture. In this regard, there is a need for a mas­sive mason­ry or well-insu­lat­ed mod­u­lar chim­ney.

Chim­neys for fire­places and their char­ac­ter­is­tics

fire­place type

com­bus­tion fea­ture

Effi­cien­cy, %

Exhaust gas tem­per­a­ture, °C

Chim­ney type

With open hearth

Air access is not lim­it­ed

15–20

Up to 600*

Brick, heat-resis­tant con­crete

With closed fire­box

Air access may be lim­it­ed

70–80

400–500

Brick, from heat-resis­tant con­crete, mod­u­lar insu­lat­ed from stain­less steel or ceram­ic, with­in the heat­ed premis­es — sin­gle-cir­cuit steel enam­eled

Fire­place stoves

Air access is lim­it­ed, gas­es are cooled pass­ing through inte­grat­ed chan­nels

Up to 85

160–230**

In addi­tion to those list­ed above: from tal­co­mag­ne­site or tal­cochlo­rite — mas­sive or with an inner pipe (steel, ceram­ic)

* — when using hard­wood, coal as fuel, as well as with exces­sive trac­tion, the tem­per­a­ture may exceed the spec­i­fied val­ue;
** — for fire­place stoves made of tal­co­mag­ne­site; for met­al — up to 400 °C

Is it possible to connect two pipes to the chimney

The ques­tion of the pos­si­bil­i­ty of con­nect­ing two fire­places to one chim­ney is debat­able. Accord­ing to the require­ments of SNiP 41–01-2003, “as a rule, a sep­a­rate chim­ney or chan­nel should be pro­vid­ed for each fur­nace. It is allowed to con­nect two stoves locat­ed in the same apart­ment on the same floor to one chim­ney. When con­nect­ing chim­neys, cuts should be pro­vid­ed in them (mid­dle walls divid­ing the chim­ney into two chan­nels. — Ed.) At least 1 m high from the bot­tom of the pipe con­nec­tion.

As for the cut, it can only be done in a brick chim­ney. If the chim­ney is mod­u­lar, it is enough to con­nect the pipe of the sec­ond fur­nace to the pipe of the first one using a tee (if the smoke chan­nels have dif­fer­ent diam­e­ters, then the small­er one is cut into the larg­er one), after which it is nec­es­sary to increase the cross sec­tion of the chan­nel. How much? Some experts believe that if the simul­ta­ne­ous oper­a­tion of fur­naces is planned, then the cross-sec­tion­al area is deter­mined by sim­ple sum­ma­tion. Oth­ers believe that it is enough to “throw” 30–50%, since two fire­box­es will warm up the com­mon pipe bet­ter and the draft will increase, but this only applies to chim­neys more than 6 m high.

When con­nect­ing two stoves locat­ed on dif­fer­ent floors to the same chim­ney, every­thing is much more com­pli­cat­ed. Prac­tice shows that such sys­tems work, but only with care­ful cal­cu­la­tion and numer­ous addi­tion­al con­di­tions (increas­ing the height of the chim­ney, installing gates after the low­er fur­nace and on the inlet pipe of the upper one, observ­ing the kin­dling sequence or com­plete­ly elim­i­nat­ing simul­ta­ne­ous oper­a­tion, etc.).

We draw your atten­tion to the fact that every­thing said in this sec­tion applies only to fire­places with a closed fire­box. An open fire­box is more fire haz­ardous and demand­ing on draft, there­fore it does not allow any “lib­er­ties” and requires the con­struc­tion of a sep­a­rate chim­ney.

How to improve chimney draft

Poor draft is usu­al­ly due to errors in the design of the chim­ney. The desire to explain it by adverse weath­er con­di­tions (changes in atmos­pher­ic pres­sure and air tem­per­a­ture) is unrea­son­able, since these fac­tors are also tak­en into account with a com­pe­tent deci­sion.

Causes of poor traction

  • Insuf­fi­cient height of the chim­ney as a whole or that part of it that ris­es above the roof.
  • Incor­rect­ly select­ed chan­nel sec­tion: too nar­row a pipe can­not ensure the exit of the entire mass of gas­es formed; too wide warms up worse, swirls of gas flow are pos­si­ble in it, and cold street air can form reverse flows.
  • Poor pipe insu­la­tion.
  • Too long non-ver­ti­cal sec­tions, espe­cial­ly at the top of the chim­ney.
  • Lack of com­bus­tion air in the room (it was nec­es­sary to pro­vide an addi­tion­al sup­ply chan­nel in the design of the chim­ney).

The over­turn­ing of the draft by the wind occurs due to the insuf­fi­cient height of the pipe above the roof. Roof ridges cre­ate air­flow tur­bu­lences; on the lee slope, it is direct­ed down­ward and is able to blow the flue gas­es back into the stack.

It is much more dif­fi­cult to deter­mine the cause in each spe­cif­ic case, since sev­er­al fac­tors often act at once, none of which plays an inde­pen­dent role. To improve draft, it is nec­es­sary to change the design of the chim­ney, some­times not too sig­nif­i­cant­ly (for exam­ple, increase the thick­ness of the ther­mal insu­la­tion on the last one and a half to two meters of the pipe). There is also such a prob­lem as exces­sive trac­tion. You can deal with it with the help of a gate. It is only nec­es­sary to pro­vide for its instal­la­tion before start­ing the instal­la­tion of the chim­ney.

In which pipes does condensate form?

The main gaseous com­bus­tion prod­ucts of car­bona­ceous fuels are car­bon diox­ide and water vapour. In addi­tion, dur­ing com­bus­tion, the mois­ture present in the fuel itself (wood) evap­o­rates. As a result of the inter­ac­tion of water vapor with sul­fur and nitro­gen oxides, acid vapors of low con­cen­tra­tion are formed, which con­dense on the inner sur­face of the chim­ney when they are cooled to a tem­per­a­ture below the crit­i­cal one (when wood is burned — about 50 ° C).

The amount of con­den­sate is direct­ly depen­dent on the area of ​​this sur­face and inverse­ly on its tem­per­a­ture. If you heat a fire­place with an exter­nal non-insu­lat­ed met­al chim­ney in the cold sea­son, the amount of con­den­sate can be mea­sured in liters per day.

A brick pipe is able to accu­mu­late heat, there­fore it behaves dif­fer­ent­ly: con­den­sate forms only at the stage of heat­ing the pipe (although this is a rather long peri­od of time). In addi­tion, the mate­r­i­al par­tial­ly absorbs con­den­sate, so the lat­ter is not too notice­able, which, how­ev­er, does not pre­vent it from exert­ing a destruc­tive effect on the mason­ry. If the inten­si­ty of com­bus­tion is low and the ambi­ent tem­per­a­ture is low, the brick may cool down and con­den­sa­tion will begin to form again.

With an insuf­fi­cient thick­ness of the insu­la­tion and a low tem­per­a­ture of the exhaust gas­es (the fur­nace is adjust­ed for long-term com­bus­tion), con­den­sate can also appear in the sand­wich-type mod­u­lar chim­ney. One way or anoth­er, it is impos­si­ble to com­plete­ly get rid of con­den­sate, it is only nec­es­sary to reduce its amount to a min­i­mum (the main means for this is the use of more effec­tive ther­mal insu­la­tion) and pre­vent leaks.

We have touched on only a small part of the prob­lems asso­ci­at­ed with the coex­is­tence of a pipe and smoke. Try­ing to answer all the ques­tions that the own­ers of fire­places have in one arti­cle is an impos­si­ble task. Often an indi­vid­ual approach is required, and, as experts note, some­times only expe­ri­ence and pro­fes­sion­al intu­ition can sug­gest the right deci­sion.

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