Is your chimney the right height?

Prompted by a question from a CSIA Certified Chimney Sweep, Ashley Eldridge, in his 21st year as the Chimney Safety Institute Director of Education, talks about rooftops and codes in this latest helpful video courtesy of csia.org. Ashley is interviewed by Tom Spalding, CSIA's Director of Marketing and Communications.
The 36-inch-above-the-peak of the roof requirement for a chimney is generally accepted because it has been proven to be important both from a functional and safety standard. How can your chimney operate to the best of its ability?
Even if your codes don't require that height, it's something to consider.

[@kyleboland6400]

This guy is the man! He politely says "most builders are stupid".

[@Martinko_Pcik]

Well, I didn't learn much from this. It just says call us, experts because the chimney is a rocket science.

[@anthonyaaron4332]

I am looking to install a larger covered patio which would result int he roof line increasing slightly more than it was. I would be within 18 inches of the flue and 6 inches from the crown. Do you know if a flue extension whether it be a clay tile or stainless flue extender/stretcher would be code compliant to get the flue >2 feet from the roof?

[@Brovioli]

Id reccomend a stainless steel flue extender with a built in cap over using terracotta, as terracotta will degrade from weathering over time and stainless steel will last much much longer.

[@leticiasilerio2239]

Do I need a chimney liner even though the exoast doesn't come through the chimney?

[@jod16]

curious about the recommended height of the chimney from the appliance, say a wood stove for minimum good draft?

[@D231991]

The core goal is to create convection; an upward pulling of the air going outward. Convection is based on pressure and pressure differences. So we know hot air rises. It doesnt sink, and it doesn't go left, right, forward or backward. The reason I mention that is because there are times a xhimney will be angled, or take a couple of right angle turns where it travels horizontally for a short distance. These turns, and the distance between them only provide resistance to what is trying to be achieved. The only way the exhaust can travel through those parts is to have enough vertical travel in the system to pull it through; and have the convection pressure be greater than the resistance given by these turns. Not only horizontal travel is not in the purview of convection, but every time the exhaust has to change directions is adds resistance as well. Straight up is the most optimal condition in oder for most efficient exhausting. As far as the distance is concerned, if you have an open fire, the exhaust rises, with zero length of chimney. A fireplace has some properties of a mild vacuum. Because air rises it must suck air from below. scenarios that would cause backdraft are, if the pressure at the top of the chimney became greater than the vacuum (low pressure system) created at the Woodstove, if there is too much resistance created by horizontal travel and turns in the exaust, if the breathing element of the woodstove becomes obstructed (system will only exhaust 100% of its capacity- so if its capacity is blocked but fire continues, the difference will be leaked into house), or if there is an opening in the pipe somewhere relieving pressure in the chimneys negative pressure system. Its not about what a minimum height is, but rather what is minimum height in the case that I have a roof, or in relation to the roof. Think about an outdoor kitchen; a Woodfield oven only needs to be above your head so you don't get smoked out all the time. But barbecue grills don't always have them. Smoke goes hand in hand with hot air, and hot air will rise as long as nothing gets in its way. 🏠👈🌬 in this picture, If a wind was to blow right to left- the upward angle of the roof would increase the pressure of the air as it approaches the peak. Then as it goes down the other side it curls down like an unfurling rug and positive pressure pushes down on the chimney, overcoming the amount of positive pressure coming out of the chimney, because it wasnt high enough over the peak.

[@markfairbanks3533]

@@D231991 if i have a chimney that is 2 feet above the peak and three feet above the roof, is there any benefit to increasing the height sai another 4 ft? Would the wood burning stove be more efficient? Would i lose less hot air during a hot burn? Or alternatively would i create more creosote? If 4ft is beneficial what about 100ft? Is there an optimal height, given say an 8in pipe?

[@D231991]

@@markfairbanks3533 you want to be 4 feet above anything within 10 feet. 2 feet means the wind pressure interacting with the ridge or roof can cause backdraft. The flu is the adjustable knob in the chimney, above the stove, and it controls how much air can freely flow "out". The draft is the + or - control on the stove which controls how much air is allowed "in" within a certain range of course. So the firebox is pressure regulated when the door is closed. When the door is open pressure still affects it. For example if smoke is dribbling out into the house, there's not enough convection, meaning the chimney isn't hot enough, but you'll notice when you get a hot fire going that problem will not be present. You can kick start the convection by lighting paper on top of you pile of tinder as close as you can get to the chimney, before lighting the tinder. So if your door is open and your chimney is maybe too close to your roof and a wind blows a certain way, it'll push the smoke back down the chimney. You can make it more than 4 feet but you won't find any 6 feet over anything within 10 feet , because 4 feet is good. Its not more efficient the longer the chimney is above the roof, but there's that 4 feet thats most efficient. So thats convection. As for the creosote- cold burning wood creates creosote. Wood that may not be seasoned, wood thats burned with as little air flow in and out as possible so that it burns longer (all night), and when hot smoke meets a cool surface it causes creosote to form on the surface. Cold air doesn't rise, so thats why outside chimney sections are insulated, in order to maintain convection. But suppose your fire was really hot, your exhausting was working well, but you didn't have insulated pipe outside- you'll build up creosote there very quickly and high risk of chimney fire. You have to lose hot air for the chimney to work properly. Those things that go in your chimney and blow hot air into the room, are cooling down the exhaust fumes, therefore collecting creosote, and also therefore reducing convection.

[@claytonroberts344]

Ok what if you have it higher then the code said but the smoke is blowing down into the neighbor's house

[@rolandhawken6628]

Bloody heck 3ft I build 2=3 meters yrds