Newmac CL 115C, Installation, Operating And Service Manual

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formation. The National Fire Prevention Association states that dilution air increases chimney deposits. In any 

case, the cooling effect of dilution air does decrease the heat transfer through the stovepipe and chimney, thus 

decreasing the system’s energy efficiency.

Creosote formation may also depend on the type of wood burned and on its moisture content. Dry hardwoods 

have a reputation for generating the least creosote, but the quantity can still be very large. No kind of wood 

eliminates creosote formation.

For a given smoke density near a surface, the cooler the surface, the more creosote will condense on it. The 

phenomenon is very similar to water vapor condensing on the outside of a glass of ice water on a humid day, 

except for an inversion – condensation occurs on the inside of a chimney, especially when cold air outside makes 

the inner chimney surface relatively cool. A stovepipe chimney outside a house on a cold day will be wet on the 

inside with creosote (including a lot of water) virtually all the time. A well insulated, prefabricated metal chimney 

has the least serious creosote problems; its insulation helps maintain higher temperatures on its inner surface, 

and its low heat capacity allows it to warm up very quickly after a fire is started. Masonry chimneys frequently 

accumulate deposits at the beginnings of fires and their interior surfaces take a longer time to warm because 

the construction is so massive. Nay type of chimney which runs up the outside of a house is more susceptible to 

creosote problems than the same type of chimney rising in the houses’ interior, due to the cooling effect of the 

colder outdoor air on the exterior chimney.

Average flue gas temperatures can be increased by minimizing the length of stovepipe connecting the stove to 

the chimney.

This, of course, will also decrease the energy efficiency of the system, and it is often true that measures which 

decrease  creosote  formation  also  decrease  heating  efficiency.  For  instance,  stoves  which  have  energy 

efficiencies due to their relatively good heat transfer (e.g. the Sevca, lange 6303 and double barrel stoves) are 

more likely to have chimney creosote problems precisely because they do such a good job extracting heat from 

the flue gases.

Generally creosote is inevitable and must be lived with. Any kind of chimney deposit decreases the system’s 

heating efficiency. Soot and dried creosote accumulations have a significant insulating effect; less of the heat in 

the flue gases transferred into a house through dirty stovepipes and chimneys. The most annoying problem can 

be creosote dripping from a stovepipe or chimney, and the most dangerous problem is chimney fires, during 

which the creosote, or its pyrolyzed residue, burns.

Creosote dripping can usually be eliminated. Joints in vertical segments of stovepipe will not leak if, at the joints, 

the smaller, crimped ends always stick down into the receiving end. (Smoke will not leak out of the joints due 

to this direction of overlay.) Since this is not the usual orientation for stovepipe, a double male fitting may be 

necessary at some point to connect the stovepipe to the stove, a prefabricated chimney, or a rain cap. Special 

drip proof adapters are available for connecting some sizes of stovepipe to Metalbestos brand prefabricated 

chimneys. Common types of stovepipe elbows can leak creosote due to their swivel joints; rigid and accordion 

type leak proof elbows are available. Horizontal or gently sloping joints between horizontal pipes and/or fillings 

are the most difficult to seal against dripping. A good high temperature sealant can sometimes help, but is no 

guarantee. The joint must also be snug, and well secured with sheet metal screws. If all joints are made leak proof, 

then the creosote will generally drip into the stove, where, when the fire is hot, it will be burned.

Chimney  fires  occur  when  the  combustible  deposits  on  the  inside  of  a  chimney  burn.  The  deposits  may  be 

‘raw’ creosote, pyrolyzed creosote, or soot. Ignition requires adequate oxygen, which is usually available, and 

sufficiently high temperatures - the same conditions as for the ignition and combustion of any fuel. Chimney fires 

are most likely to occur during a very hot fire, as when cardboard or Christmas tree branches are burned, or even 

when a stove burns normal wood, but at a higher than normal rate. A crackling sound can often be heard at the 

beginning of a chimney fire. As the intensity of the fire rises, the stovepipe will sometimes shake violently, air will be 

very forcefully drawn in through the stove, and the stovepipe may glow red hot. A tall plume of flame and sparks 

can be seen rising from the top of uncapped chimneys.

The most effective way to suppress a chimney fire is to limit its air supply although both water and salt are sometimes 

suggested if a relatively airtight stove is the connected appliance. This is easily done by closing the stove’s air-

inlet dampers, if all the stovepipe and/or chimney joints are tight, and if no other appliance is connected to the 

same flue.

In a properly designed and maintained chimney, the only potential hazard related to chimney fires is ignition 

of the building’s roof or surroundings due to sparks and burning embers coming out of the top of the chimney. 

A spark arresting screen can decrease, but not eliminate this possibility, but spark screens themselves are often 

not suitable for use with wood fuel because they can become clogged. The chimney itself and the stovepipe, 

when properly installed, are intended to withstand an occasional chimney fire without danger of ignition of their 

surroundings. During a chimney fire, one ought to check the roof and surroundings, and possibly wet down critical 

areas. If the chimney may not be up to safety standards, one should also keep a close watch on all surfaces near 

the chimney.