Chimney height on roof

[David P. OKeefe]

I always thought a chimney needs to be at least 3 feet above a roof. But in looking closer at the Inspection Graphics it states a minimum of 2 feet for gas vent or type L vent. The chimney in the pixs is from the oil furnace and is 2 feet high. Is this OK or should it be three feet?

[David P. OKeefe]

I measured it from the low side, but on the ridge side it is probably only a foot and a half tall. Should it be 2 feet at the ridge side?

[Jeffrey R. Pope]

Strictly speaking of the projection of the chimney. . .

3 ft. tall min - measured from the tallest side.
2 ft. higher than any wall/ridge within 10 ft.

[Larry D. Kage]

Originally Posted by dokeefe

Should it be 2 feet at the ridge side?

Yes, minimum...

[David P. OKeefe]

Originally Posted by jpope

Strictly speaking of the projection of the chimney. . .

3 ft. tall min - measured from the tallest side.
2 ft. higher than any wall/ridge within 10 ft.

So, it's too short on both sides. No difference from gas, oil, wood chimneys?

[Jeffrey R. Pope]

If it's a "chimney," those are the requirements. If it's a "vent" (gas-fired, oil-fired), these requirements do not apply.

[Bob Elliott]

Originally Posted by jpope

If it's a "chimney," those are the requirements. If it's a "vent" (gas-fired, oil-fired), these requirements do not apply.

This is a metal chase surrounding a vent.
What say you?

[Jeffrey R. Pope]

Depends on the slope of the roof and the appliance it serves, but generally speaking for what is pictured. . .

2 ft. minimum projection from the roof and 2 ft. above a wall or similar obstruction within 10 ft. of the termination.

[Bob Elliott]

Originally Posted by jpope

Depends on the slope of the roof and the appliance it serves, but generally speaking for what is pictured. . .

2 ft. minimum projection from the roof and 2 ft. above a wall or similar obstruction within 10 ft. of the termination.

OK ,from the earlier response I thought you were viewing it as a wood burning fireplace chimney.

I think many are not clear on the difference and bet seeing the fake brick(metal) chase would put them in 10/3/2 mode.

[David P. OKeefe]

Originally Posted by belliott

This is a metal chase surrounding a vent.
What say you?

Here is another pix. It is a vent from an oil fired furnace made to look like a brick chimney. So the 2/10/3 rule doesn't apply? But it still needs to be at least 2 feet above the ridge.

[Bob Elliott]

Originally Posted by dokeefe

Here is another pix. It is a vent from an oil fired furnace made to look like a brick chimney. So the 2/10/3 rule doesn't apply? But it still needs to be at least 2 feet above the ridge.

That is pretty much what I was saying.

[David P. OKeefe]

OK, anyone., what is the difference between these two. A block chimney with a tile flue from a gas furnace and this metal flue from an oil furnace. Why are the requirements not the same? One is required to be three feet high but the other one only 2 feet high? Am I missing something?

[ROBERT V. YOUNG]

for O'Keeffe about false chimney.
Its a chase enclosure and there are plenty of them in western part of Montreal Quebec Canada.They can be for wood,an oil furnaces.Cheaper then doing a brick double width and single width Terra cotta lined chimneys.
You see them mostly on double cladded facade exterior homes.Lower part brick about first 8 to 10 feet and upper part siding.I rarely see this on fully brick clad homes but I have seen a few and far between.Maybe after thought.
For O'Keeffe on brick and block chimney.
Even the ridge vent is so close to the spark arrester from the chimney ,no crown to control rain dripping , and drafting ,stop spillage and if there is back drafting all that startup and shut down smoke goes right into the home along with Co's from burning..
From the pictures I see its a real hazard.
Just my opinion.
Now to answer you question its fire hazard that is caused from wood burning fireboxes and fire places and the sparks on the roof from chimneys built to close to the roof that is why they have a hight restriction and should have spark arresters on top of the crown or cap as some people call it.The hight regulation is for smoke and spark that has to draft properly over a roof and not drift into windows and roof vents.As for oil stoves the heat is not as hazards and no sparks but there is Co's that have to be carried away by drafting so hight requirements are in place.
If you google chimney hight requirements you should be OK and InterNACH has in depth building code on this.
Hight restrictions for oil and wood burning fireplaces.
1 : brick chimneys must be higher because of outlet is larger '' FLUE'' for spark and fire concerns
2 : oil chases lower because outlet is smaller ''flue'', no chance of spark fires.
I hope this helped you.
I am a mason and build chimneys and if you need more help email me and if I have the time I would be glad to answer you question but everything is on internachi .
Sorry if my explanation is all over the place .I am tired.

[David P. OKeefe]

I am asking why are the height requirements different, or am I misinterpreting/misunderstanding something?

[ROBERT V. YOUNG]

Both of these would be breaking code in Montreal Canada.Read hight and clearance regulations for chimneys.No more block chimneys in Montreal thats for most of the areas I have looked into anyway and the clearance is off spec that for sure.