Questions about my new chimney install...

[Hoozie]

Finally looking to replace our chimney with something that's correct, and I had some questions before I ordered everything.

1. Does this look like a decent plan? The attic hatch is in the way, so I had to avoid it. Can't go straight up without the same issue, and I don't feel like going through the roof and moving the hatch at the moment.

2. I presume going with 15° offsets is better than 30°?

3. I think I'll need to add another 4' (and a roof support) to what the picture shows to get to 15' outside. From through the wall to the peak is 9.5', and I lose some draft with the 90s, so more outside is probably better? I'm also at 4200' elevation.

4. Inside, is there a minimum vertical I need before going horizontal? I was thinking about rebuilding the hearth to be a foot taller, which would reduce my vertical to ~6" before going into the 90° piece.

5. If I get galvalume for the horizontal piece, I can paint it black to match the interior DVL, right?

6. It looks like my existing horizontal and Tee are triple wall. They are painted so I can't see any part numbers/brands. Probably better to just get a new Tee? Although if I can strip the paint and make them shiny again, I might be able to reuse them?

7. DuraTech or DuraPlus? Prices seem similar. Would one or the other be better for this install?

Anything I'm missing? Thanks!

 

[webby3650]

Use dura-tech. Dura-plus is a much cheaper pipe, and is air cooled. I would not use dura-plus unless I had no other option.
Do as much vertical pipe as possible before turning horizontal. 2'-3' is best. There is no need to get the galvi pipe. You can paint SS pipe just as easily, get some satin black stove bright paint, it's the same paint dura vent uses. 30 degree offsets are readily available, these will do the job just fine.

 

[begreen]

He might want to use DuraPlus if the hole is already sized for the larger dimension of triple wall. Other than that I concur and would prefer DuraTech.

 

[Hoozie]

Looking at the dimensions of my thimble, it appears to be Duratech, so I'm thinking I can reuse my Tee and the 36" piece, and the DVL adapter.

Do as much vertical pipe as possible before turning horizontal. 2'-3' is best.

eek. I currently only have 18". If I build a taller hearth that would of course be shortened. I could extend that by moving the thimble up the wall, but looking at the weather, I really don't want to that if I can avoid it.

I'm looking at woodstovepro.com, and they appear to have the 15* offsets. Although overall cost comes out about $100 more going with the more expensive 30* offsets.

 

[Hoozie]

And now for a complete change in plans...

It works out to be $3-400 cheaper if I go straight up, use 45° DVL offsets (to avoid the peak), through the ceiling, then straight up through the roof. Then I can eventually raise the hearth and not run into the horizontal through-wall section.

A few more questions:
1. Can the 45° DVL section go right into the ceiling support box, or do I need 18" clearance from the ceiling to the 45°?
2. I like the look of this ICC flashing (http://www.stoves-pipes.com/ICC-EXCEL-FLASHING-METAL-ROOF-8-12-12-12-6-I-D-p/icxf6emfb.htm). Should I get a vented or non-vented one?
3. 6DVL-12ADJ is a 12" adjustable length of DVL. It says it adds 2"-10" of length, so does that make its overall length vary from 14"-22"? I would need it for the diagonal section to get the offset width correct.
4. When do I need to consider adding bracing to the chimney above the roof? Currently the plan is to have ~2.5' above the peak, but that puts me right at 15-16' to the floor (the 30NC manual says 15' from floor to cap? I'm at 4200' elevation)

 

[webby3650]

The DVL elbows can go right up at the box, they only need a 6" clearance to combustibles.
You are correct about the slip, it will add 2"-10" to what ever piece you add it to.
That flashing is great, I don't see any reason to have a ventilated flashing. I can help you out with any installation questions you might have on this.
You need to add bracing if the chimney is more than 5' above the flashing. Screw the pipe to the flashing with 1/2" screws for added support.

 

[Hoozie]

Ohh, so the slip piece goes over another existing pipe. I was thinking it came with two halves that extended into/out of each other. Good to know.
So I probably won't need another brace inside just below the flashing, if I use 1/2" screws from the flashing to the pipe? The attic is only 6.5' tall, so I'll only have 2 pieces of pipe above the ceiling support.

Thanks

 

[Hoozie]

Quick question; Single story house, going through the ceiling into the attic, then through the roof.

I have a round support box. Do I need a Firestop Radiation Shield? The book says they're needed for multi-story installs, but doesn't explicitly say they're not needed for single story installs. "Needed at the 2nd/3rd floor ceiling, and where the chimney penetrates the attic"

Also, the book says not to attach the roof flashing to the stove pipe?

 

[begreen]

The support box is the first firestop. Sounds like you just need an attic insulation shield on it.

 

[webby3650]

I would definitely shoot some short screws through the flashing into the pipe. They just say that to prevent people from using long screws the that penetrate the inner wall.
It does several things. The screws keep it from moving around, it also prevents the pipe from being pulled up out of the support box when it's cleaned.

 

[bholler]

I was told to never put screws through the flashing because it then does not allow for expansion.

 

[webby3650]

I've never heard that before. I can't see that being an issue at all. Its so much more secure with screws in it.
My first super vent system would actually move in heavy winds. The flashing was sloppy enough to allow a lot of movement. And you have to hold the pipe down while you broom it.

 

[bholler]

i know they can moce if the flashing is loose but how would the pipe expand with it attached at the top?

 

[webby3650]

i know they can moce if the flashing is loose but how would the pipe expand with it attached at the top?

How much does it expand?

 

[bholler]

I dont know that would vary greatly depending upon how tall it was what temp it was to start with ect.

 

[Hoozie]

I was wondering about the expansion as well. In my case, I think I'll end up with a 3' and 5' section of duratech, with the 5' piece going through the flashing. I guess if the chimney did get slightly taller when hot, it would just bow the flashing up a tiny bit.

My other idea was to put a wall brace on a 2x4 between the rafters inside, giving a second point to hold the pipe steady.

 

[webby3650]

It does not expand enough to make any difference. Our store has been screwing them to flashings for 40 years, and this is the first time I've even heard it mentioned.
If it did, a lot of the accessories would cause problems. Wall bands, roof supports, intermittent tee supports, all these would experience issues if this was a real problem. We service and inspect everything we install, I've never seen or heard of any issues in regards to expansion.

 

[BCC_Burner]

It does not expand enough to make any difference. Our store has been screwing them to flashings for 40 years, and this is the first time I've even heard it mentioned.
If it did, a lot of the accessories would cause problems. Wall bands, roof supports, intermittent tee supports, all these would experience issues if this was a real problem. We service and inspect everything we install, I've never seen or heard of any issues in regards to expansion.

Agreed, how much do you think high temperature steel really expands and contracts with a couple hundred degree change in temperature. I can tell you from our production work involving bonding steel to UHMW and carbon fiber under heat and pressure, that there is very little expansion and contraction.

 

[fire_man]

Agreed, how much do you think high temperature steel really expands and contracts with a couple hundred degree change in temperature. I can tell you from our production work involving bonding steel to UHMW and carbon fiber under heat and pressure, that there is very little expansion and contraction.

I found this at http://www.engineeringtoolbox.com/thermal-expansion-pipes-d_283.html
For stainless steel, they list the expansion coefficient = 12 10e-6 in/inF, so for 100 feet of pipe it would expand even more than in this example. Bottom line, 100 feet of alloy steel expanded 1.728", so stainless should expand 50% more to about 2.5". This is only for a 180 degree temperature change. Seems like way more than I would expect.

The temperature expansion of pipes depends on the start and final temperature of the pipe and the expansion coefficient of the piping material at the actual temperature. The general expansion formula can be expressed as:

dl = α Lo dt (1)

where

dl = expansion (m, inches)

Lo = length of pipe (m, inches)

dt = temperature difference (oC, oF)

α = linear expansion coefficient (m/moK, in/inoF)

Mean expansion coefficient may vary with temperature as:

Mean Expansion Coefficient - α - (10-6 in/in oF)

Example - Thermal Expansion of Heated Alloy Steel
100 feet of alloy steel pipe is heated from 32 to 212oF. The expansion coefficient is 8 10-6 (in/inoF).

The expansion of the pipe can be calculated as:

dl = (8 10-6 in/inoF) (100 feet) (12 in/ft) ((212 oF) - (32 oF))

= 1.728 inches
​

 

[bholler]

I dont know if it expands enough to make a difference but if you really look at most of the supports they really only stabilize the chimney laterally. That and the fact that the instructions dont say to do it is enough to tel me not to do it. I really dont know that it will make a difference but i really don't see a reason to do it. And have they been making class a chimneys for 40 years now i didnt think it was anywhere near that long.

 

[Hoozie]

Another silly question: Due to terrible construction, the drywall in my ceiling has a 1/12 drop between the joists where I'm installing the chimney. As such, I'll probably need to drill another hole or two in the round support box to get three screws on the one side. I know you're not supposed to modify anything, but does adding another hole really count?

If I had realized this before buying everything, I probably would have gotten a square support box and just dropped it down the requisite amount.

 

[webby3650]

That's we just use the square boxes, unless the customer requests a round support. Adding screws won't hurt anything, go for it.

 

[Hoozie]

Ok, another question: I have the 6DVL-AD stovetop adapter. Is that what I need to go from the stove to DVL? The adapter sits really loose in the flange on the stove.

More importantly, it sits low enough that I don't have access to the bolt holes in the flange, unless I don't drop it down all the way. That is making it difficult to keep it level while driving the 4 screws in.

Or is there a different adapter I need?

Edit: It looks like I may need the 1677 adapter, but I haven't seen anything that explicitly says it connects to DVL. Any idea if it does?

 

[webby3650]

That adaptor is for single wall pipe. The DVL adaptor doesn't always work out, some flue collars just won't accept it. You can measure out the holes on your flue collar and transfer them to the adaptor. You can then drill out the outer wall big enough to get a screw through the flue collar and into the inner wall of the adaptor.

 

[Hoozie]

I was wondering if I could do that; drill holes in the outer wall of the adapter to get access to put screws in. I will probably try to do that next week sometime when I get a brief warm spell. With some cold weather coming next week I needed to get it together.

In the meantime, I did this:

Took the 6DVL-ADC adapter and crimped the smaller diameter side. This fits very snug into the stove collar, with three screws to keep it in place. The other end fits pretty snug into my DVL, though it doesn't have anything but gravity holding it down. The flanges are all correct to keep any creosote (hah!) going down into the stove.

With it being 65° this afternoon, the new chimney drafted better than the old one did when it was cold

Now to decide if I want to run the OAK through the old thimble

Now, some pictures:



Thanks for all the help! I really do appreciate it