Critique my chimney design (brutal honesty please)

[Badfish740]

Now that fall is creeping in I need to get my chimney installed ASAP. I called for the permit application this morning and I'll be ordering parts soon. Some of you may have seen my post a while back regarding dodging a first floor window on the way up the side of the house-I measured it out and it's not as big a deal as I had thought. It should be easily taken care of with two 15 degree elbows, which from what I've read, should have a negligible effect on draft. The stove that I'm venting is an Englander 28-3500 Add-on furnace. Please refer to the rough drawing (it's a crude scale, 1 mm = 1") when reading the description-starting from the bottom:

- The thimble will be installed in what was a basement window. The wooden frame will be removed and the area not occupied by the thimble will be sealed with non-combustible materials (bricks and mortar)-the top edge of the window is actually the sill plate of the house, but since Class A pipe will be used to transition from inside to outside, the thimble will ensure proper clearance.

- The support bracket will be attached to the block foundation wall via Tapcon concrete anchors. A Class A tee will transition the pipe 90 degrees up the side of the house.

- The first vertical section of pipe will be 36" and then an offset will be used to direct the chimney around the 1st floor window using two 15 degree elbows. A band will be used to reinforce the pipe just below the first elbow.

- From the 15 degree elbow five lengths of 36" pipe (the bottom of the first pipe will be reinforced with another band) will continue up the side of the house.

- One band will be used in the middle of the five length run, and one band will be used just before the run clears the roofline. I also considered using an adjustable roof support (looks like a band clamp with submarine bow planes attached to the sides) at this point I needed to add a length of pipe or ever wanted to in the future. Hart and Cooley states that an offset can support a maximum of fifteen feet of pipe, which will bring the top of the chimney well past the peak of the roof, but I'm wondering if I should add one more 36" section (which would necessitate the adjustable roof support) so as to negate any possible wind turbulence that might result from the masonry chimney for the oil burner being located nearby. Also, it probably couldn't hurt for draft reasons either since I will have two 90 degree bends and two 15 degree bends in the system.

- The top will be guyed of course due to the height of the chimney above the roofline.

I'm sure this seems like a pretty anal post, but in pricing this stuff out I'm looking at laying out a lot of money and I want to make sure that I do it right the first time. Please let me know what looks good, what doesn't look good, and where there is room for improvement.

 

[Sleepy]

Why so high? You only need to be 2' higher than anything within a 10' radius.

Do you have trees nearby or something else not shown in the picture?

 

[MountainStoveGuy]

it looks great to me, he needs to be higher then that chimney if its within 10. It looks like it might be. replace the guy wires with conduit supports. Rigid is way better then wire. Flatten the ends, make a support band to go around the pipe with 1" holey iron, bolt the conduit to the iron, and screw it to the roof.

 

[MountainStoveGuy]

All that said, from a design standpoint it looks great. From a functional standpoint who knows. Thats alot of exposed chimney, and lets hope that basement is not a negative pressure zone. If it is, the chimney will help neutralize the basement and destroy draft. I would not put that design on my house, but the design looks safe and by the book.

 

[Brian VT]

Very similar to mine, except mine is on the side of the house.
I get a decent draft. I've had it suck a ball of lit newspaper up the chimney.
I mostly burn 24/7. If I do let it go out, I sometimes have to induce a draft. I always check for draft, with cigarette smoke, before lighting.
My only concern of your system is the wall thimble. You mentioned the sill being at the top of the opening.
You'll need a 12"x12" hole for the thimble. You'll also need to maintain clearance to the interior ceiling above the horiz. pipe.
Are you using double-walled pipe inside ? I've got about 10" above mine (I think 8" is legal?) and the ceiling still gets pretty warm.
Pics of my install are here, if you care to look.: http://s388.photobucket.com/albums/oo329/BrianVT16/Chimney/
On the 2nd page you'll see the roof supports I bought (as opposed to the guy wires you mentioned).
I spent about $1300 for this Dura-Tech chimney. My only complaint is the transition from dbl. wall to class A.
There's not a good seal and I do find a bit of creosote near there in an otherwise clean chimney.

 

[Brian VT]

i wouldnt poke into my roof ! chimni dont look like its going anywhere to me

Nice post ! Tell us more !

 

[Badfish740]

All that said, from a design standpoint it looks great. From a functional standpoint who knows. Thats alot of exposed chimney, and lets hope that basement is not a negative pressure zone. If it is, the chimney will help neutralize the basement and destroy draft. I would not put that design on my house, but the design looks safe and by the book.

Can someone elaborate on this a bit? I should have mentioned that I will be routing outside air into the basement, I'm just not sure how yet. What I could do is instead of bricking up the remaining window space simply installing some sort of perforated metal or grating so the furnace has plenty of air. Would this help with a negative pressure situation in the basement? As for the proximity of the oil furnace chimney I think I'll simply add another length to put it well beyond the limit.

Very similar to mine, except mine is on the side of the house.
I get a decent draft. I've had it suck a ball of lit newspaper up the chimney.I mostly burn 24/7. If I do let it go out, I sometimes have to induce a draft. I always check for draft, with cigarette smoke, before lighting.

I most likely won't be able to burn 24/7 yet (at least until my wife becomes comfortable tending the stove until I get home), so I'm sure I'll have to induce draft at times, I just want to be sure that if the barometric pressure is high and I don't have the stove running at full tilt that I'm not going to smoke out my basement.

My only concern of your system is the wall thimble. You mentioned the sill being at the top of the opening.
You'll need a 12"x12" hole for the thimble. You'll also need to maintain clearance to the interior ceiling above the horiz. pipe.
Are you using double-walled pipe inside ?

I should have been more clear on that-clearance is so tight inside that I have no choice but to use Class A-I have maybe 3" inside so I'm actually going to take the additional step of covering the joists with Hardi-Board. The Class A will come in through the thimble where it will attach to a tee. The other (vertical) end of the tee will have a stove pipe adapter to transition to stove pipe into the furnace. Anyway, back to the main topic-I'm going into this whole thing that given the fact that I have direction changes in the system that height certainly can't hurt. Will I be ok so long as I provide enough outside air?

 

[Brian VT]

I think you need a UL thimble (12"x12") to meet code. Maybe you don't have to get inspected and you'll just use your best judgement.
We don't have any codes, but I went by the book.
I wanted my outside tee/cleanout higher off the ground. I didn't, because I would have had to face the same dilema as you with the interior ceiling.
How long is the horizontal run inside ? This will greatly affect your draft. You'll want to slope the horiz. up at least 1/4" per foot of length.
That interior tee will add a bit more drag than a 90 deg. bend, too, I think. I don't have outside air but my house isn't very "tight".
Also, the Hardi-Board will transmit heat. One tends to think that if "fire" can't get at wood then it won't burn. Not true.
I've seen wood-framed hearths, covered with 1/2" cement board and tile, taken apart. The wood joists were black and could have
"spontaneously" combusted the next time the stove was run....or the one after that...
My interior dbl. wall pipe gets hot and class A gets hotter than you might think, especially if you happen to over-fire.
You have to plan not just for everyday heating but for the time everything goes wrong.
At the least, I would put insulators between the joists and the Hardi-Board. I think you're too close for comfort, though, i.m.o.

 

[Brian VT]

Thats alot of exposed chimney, and lets hope that basement is not a negative pressure zone. If it is, the chimney will help neutralize the basement and destroy draft.

Can someone elaborate on this a bit?

Ideally your chimney would be in the center of the house, where it's warmest. A cold chimney doesn't tend to draft
and a cold chimney can cool dirty smoke and produce creosote.
An exterior chimney, especially a metal one, cools easily. It's a good idea to, at least, enclose them with
3 exterior walls and open the (4th) inside wall to the house where it will draw warmth from.
Negative pressure has been discussed at great length here. A quick search will give you tons of info and most
of the Class A manufacturers' sites explain it well also.

 

[Yagminas Masonry and Wood-heat]

Why so high? You only need to be 2' higher than anything within a 10' radius.

Do you have trees nearby or something else not shown in the picture?

Our code here in Ontario is at least 3' out of the roof AND 2' above anything cumbustible within 10'. So when I do an inspection I always look at the 3' rule first and then the 10'/2' rule.

 

[Yagminas Masonry and Wood-heat]

it looks great to me, he needs to be higher then that chimney if its within 10. It looks like it might be. replace the guy wires with conduit supports. Rigid is way better then wire. Flatten the ends, make a support band to go around the pipe with 1" holey iron, bolt the conduit to the iron, and screw it to the roof.

Why would it have to be higher than the other chimney? It's non-combustible and theoretically you would then be putting the other chimney not-to-code.

 

[Brian VT]

...and theoretically you would then be putting the other chimney not-to-code.

LOL ! I wouldn't have thought of that. Funny, but true.

 

[MountainStoveGuy]

it looks great to me, he needs to be higher then that chimney if its within 10. It looks like it might be. replace the guy wires with conduit supports. Rigid is way better then wire. Flatten the ends, make a support band to go around the pipe with 1" holey iron, bolt the conduit to the iron, and screw it to the roof.

Why would it have to be higher than the other chimney? It's non-combustible and theoretically you would then be putting the other chimney not-to-code.

yep, kind of a catch 22 eh? when the closest thing within 10 is the other chimney, then what? I guess in real life one is going to be affected by the other depending on the wind direction. But when you have two flues close to one another one has to be taller then the other or they can bring back smoke down the other chimney, no real good solution here, but i would like to see the class A chimney taller then the brick. The appliance on the class A chimney is more likely to be more draft sensitive then the appliance hooked to the big masonry one. Also, the big masonry one is going to create more of a air pocket then the small class A one. Personally, i would advise the smaller chimney be taller then the one with a lot of mass.

 

[Badfish740]

I think you need a UL thimble (12"x12") to meet code. Maybe you don't have to get inspected and you'll just use your best judgement.
We don't have any codes, but I went by the book.

We definitely have inspection here-I was mistaken on the measurement by the way. The thimble I'm using (Hart and Cooley) is 16 x 16 with an 8 and 1/8" centered opening, so if I mount it resting on the bottom of the window frame (on the bare block of course) I will have 7 and 1/4" to the wood sill. I would think that would be sufficient for Class A no?

How long is the horizontal run inside ?

Only three feet which I'll try to slope 1/2" per foot.

The only thing that's worrying me now is the "dueling chimneys" which I guess I'll just have to hash out with the inspector.

 

[Brian VT]

The thimble I'm using (Hart and Cooley) is 16 x 16 with an 8 and 1/8" centered opening, so if I mount it resting on the bottom of the window frame (on the bare block of course) I will have 7 and 1/4" to the wood sill. I would think that would be sufficient for Class A no?

If you have a 16x16 hole for a proper thimble, even if it was all framed with wood, you are okay.
Does this still place your interior pipe 3" from the ceiling ?

I think you'll be fine on the roof, assuming the other chimney is all non-combustible material.
If he wants you to go taller, then you may get the benefit of a better draft. The only bummer is having
to take it down for cleaning.

 

[crazy_dan]

dueling chimneys ????? is their not houses with 2 or more flues under the same cap? with differing heights? maybe just an inch or two. but I believe that it reads COMBUSTIBLE last time I check brick and mortar is not combustible neither is steel.

I think as far as the run of the chimney pipe itself I think is fine and the extra height will not hurt a thing in fact will probably be better since there is a small horizontal run and at least 4 direction changes.
outside influences will not be known till after it is in and running, which is unfortunate.

 

[MountainStoveGuy]

the 10/2/3 rule is not about combustibles, its about airflow and turbulence. Well the 3 part of that rule is about combustibles, but that doesn't apply here.