Designing a chimney without mistakes

Today, brick pipes have been replaced by sand­wich-mod­ule struc­tures (steel + insu­la­tion). With obser­vance of pro­duc­tion and assem­bly tech­nolo­gies, they pro­vide fire safe­ty and excel­lent trac­tion. How­ev­er, some­times the chim­ney refus­es to work prop­er­ly. On the forum of the site and spe­cial­ized Inter­net resources on heat­ing, we chose descrip­tions of the symp­toms of the most com­mon “dis­eases” of chim­neys. Engi­neers of man­u­fac­tur­ing com­pa­nies and build­ing prac­ti­tion­ers helped us in mak­ing “diag­noses” and search­ing for “med­i­cines”.

The fire­place does not melt well, the fire­wood does not burn, but smol­ders, the glass of the fur­nace door is quick­ly cov­ered with soot, wisps of smoke break through the air holes.

Signs of poor trac­tion are list­ed. The most com­mon rea­son is severe con­t­a­m­i­na­tion of the chim­ney. If a new­ly built fire­place smokes, then a chim­ney of insuf­fi­cient length (less than 5 m), too many bends, nar­row­ings and extend­ed hor­i­zon­tal sec­tions can be a source of prob­lems. With insuf­fi­cient trac­tion, it often helps to increase the height of the pipe by 1–2 m, and it is nec­es­sary to use only well-insu­lat­ed mod­ules and attach the exten­sion to the build­ing struc­tures with cable braces or studs so that it is not blown away by the wind. If after this the draft does not return to nor­mal, the chim­ney needs a com­plete recon­struc­tion — an increase in diam­e­ter and a straight­en­ing of the “main”. Anoth­er way is to install an elec­tric smoke exhauster, but it has draw­backs (we will talk about devices to improve trac­tion sep­a­rate­ly).

The reason for the poor performance of the chimney is most often the mistakes of designers and installers, and only sometimes — manufacturers

As a rule, the fire­place heats up nor­mal­ly, but occa­sion­al­ly large clouds of smoke break through the air holes.

This phe­nom­e­non is called pull-back. It is pos­si­ble that the chim­ney is not prop­er­ly aligned rel­a­tive to the ridge, and down­ward swirls of air flow peri­od­i­cal­ly occur in the area of ​​​​the head. The prob­a­bil­i­ty of draft over­turn­ing by the wind increas­es with insuf­fi­cient insu­la­tion of the upper part of the pipe: the smoke has time to cool, its speed decreas­es sharply, and gusts of wind eas­i­ly dis­rupt the oper­a­tion of the fire­place. The cause of the trou­ble may be an unsuc­cess­ful umbrel­la design that cre­ates aero­dy­nam­ic resis­tance.

Chim­ney insu­la­tion helps to solve the prob­lem. If it is not pos­si­ble to replace the upper mod­ules, you should order a shell (out­er cas­ing), the diam­e­ter of which will allow you to install an addi­tion­al lay­er of ther­mal insu­la­tion with a thick­ness of 30–50 mm. It is bet­ter to use spe­cial basalt wool insu­la­tion, such as Rock­wool Fire Batts (non-foiled). Wind vane deflec­tor can become an addi­tion­al pro­tec­tion against over­turn­ing thrust by the wind.

The fire­place con­sumes a lot of fuel and gives lit­tle heat.

A straight-through chim­ney of cir­cu­lar cross sec­tion with a height of more than 6 m often draws too much, and it is not pos­si­ble to slow down com­bus­tion, even by com­plete­ly clos­ing the dampers of the air inlets (after all, a resid­ual gap is always pro­vid­ed). In this case, the effi­cien­cy of the device is very low.

To reg­u­late the draft, it is nec­es­sary to install a gate at the out­let of the fur­nace (alas, you have to dis­as­sem­ble the entire pipe). In addi­tion, heat-remov­ing or heat-stor­ing mod­ules in the low­er part of the chim­ney will be use­ful. The for­mer are equipped with met­al ribs and oper­ate on the prin­ci­ple of a radi­a­tor, the lat­ter are dou­ble-walled, but the insu­la­tion in them is replaced by stone chips or per­lite sand.

Some sec­tions of the chim­ney are very hot, some­times their tem­per­a­ture exceeds 100 ° C.

Most like­ly, this prob­lem is caused by local ther­mal degra­da­tion or shrink­age of low-qual­i­ty insu­la­tion. The prob­a­bil­i­ty of leak­age of the inner tube is small, but still it can­not be ruled out. Over­heat­ing of the shell is dan­ger­ous, espe­cial­ly if com­bustible struc­tures are locat­ed near­by (clos­er than 0.5 m), because over­dried wood can ignite spon­ta­neous­ly at a rel­a­tive­ly low tem­per­a­ture. In addi­tion, the dete­ri­o­ra­tion of ther­mal insu­la­tion leads to an increase in the amount of smoke con­den­sate: the con­tain­er for it will quick­ly over­flow, and if equip­ment is installed that allows the con­den­sate to be drained into the sew­er (neu­tral­iz­er), the con­sump­tion of an expen­sive reagent will increase.

A chim­ney with a sim­i­lar defect must be replaced. As a tem­po­rary mea­sure, you can lim­it your­self to installing an addi­tion­al ther­mal­ly insu­lat­ing cas­ing (for exam­ple, from GVL, filled with stone wool), but first you need to check the con­di­tion of the walls of the smoke chan­nel — this ser­vice is pro­vid­ed by ser­vice com­pa­nies.

An incorrectly selected deflector nozzle can cause sudden draft disturbances and carbon monoxide penetration into living rooms.

Once the pipe was very hot all over, crack­ling was heard in it, the smell of hot met­al appeared in the rooms. Then every­thing returned to nor­mal, only the gal­va­nized umbrel­la dark­ened and began to rust.

The clas­sic symp­toms of a soot fire in a pipe are described. A chim­ney made of qual­i­ty mate­ri­als (work­ing chan­nel — stain­less steel grade 321, 430 or 439 accord­ing to AISI clas­si­fi­ca­tion, insu­la­tion — basalt or ceram­ic wool) must with­stand such a test. After the inci­dent, it is nec­es­sary to mon­i­tor the tem­per­a­ture of the shell for some time, and in addi­tion, it is advis­able to take pho­tographs of the smoke chan­nel. In gen­er­al, it is bet­ter to pre­vent a fire in the chim­ney, for which it is enough to clean the chim­ney once a year (when using long-burn­ing stoves — 2 times).

After sev­er­al years of oper­a­tion, con­den­sate began to seep through the joints, espe­cial­ly in the upper part of the chim­ney, in the attic.

Obvi­ous­ly, the chim­ney is poor­ly insu­lat­ed, which caus­es intense for­ma­tion of con­den­sate, and at the same time it is incor­rect­ly man­u­fac­tured and assem­bled: its ele­ments are ori­ent­ed down­wards with sock­ets. (It is nec­es­sary that the sock­ets of the smoke chan­nel parts face upwards.) Try­ing to seal the joints with oven sealant is use­less in this case. The chim­ney can be oper­at­ed for some more time, but after wait­ing for the warm sea­son, it should be recon­struct­ed.

In the spring, brown streaks began to be seen on the roof, near the chim­ney.

Most like­ly, an umbrel­la of con­sid­er­able size is to blame, on the cold sur­faces of which con­den­sa­tion fell out. Even more caus­tic liq­uid can form on the walls of a met­al box with a roof, arranged for sev­er­al pipes (flue and exhaust). Such a box must be filled with expand­ed clay almost to the pipe cuts, and the area of ​​u200bu200bthe umbrel­la should be reduced. A lit­tle rain and snow is harm­less to the chim­ney and heat­ing equip­ment, but it is almost impos­si­ble to remove traces of con­den­sate from the roof and walls.

More traction

Quite often, to cor­rect errors made in the design of the chim­ney, spe­cial noz­zles are used on the pipe.

Vane deflec­tor clos­es the mouth of the chim­ney from hor­i­zon­tal and vor­tex air flows. It con­sists of an inclined shield mov­ably fixed on a ver­ti­cal axis, equipped with a “feath­er­ing”, due to which the shield is locat­ed on the wind­ward side of the pipe head. In mod­er­ate winds, the deflec­tor sta­bi­lizes and enhances trac­tion, great­ly reduc­ing the like­li­hood of it tip­ping over.

Rotat­ing deflec­tor is a spher­i­cal tur­bine. Under the influ­ence of wind (regard­less of direc­tion), its blades rotate and cre­ate a vac­u­um in the pipe. Such devices have proven their effec­tive­ness as ele­ments of roof ven­ti­la­tion sys­tems. How­ev­er, they are almost unsuit­able for chim­neys, since they wors­en draft in calm weath­er, and in win­ter they can freeze, com­plete­ly block­ing the path to flue gas­es, which is extreme­ly dan­ger­ous.

Elec­tric smoke exhauster The sim­plest design is a noz­zle on a pipe with a fan, the blades of which rotate direct­ly in the smoke chan­nel. It is desir­able that the per­for­mance of the device can be adjust­ed — in this way, it will be pos­si­ble to pro­vide quick kin­dling, and then mod­er­ate the crav­ings.

The smoke exhauster is reli­able, since its mov­ing parts are pro­tect­ed from mois­ture and ice (as well as from the effects of caus­tic sub­stances and high tem­per­a­tures), eco­nom­i­cal (pow­er con­sump­tion 40–100 W / h) and almost silent. Its main dis­ad­van­tages are the need for peri­od­ic clean­ing of tar and soot and depen­dence on pow­er sup­ply. How­ev­er, the sec­ond dis­ad­van­tage is eas­i­ly over­come by installing a back­up pow­er source. A smoke exhauster is some­times used as a “cure” for poor draft, but it is main­ly intend­ed for the con­ve­nience of using open-hearth fire­places and island hearths.

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