wood stove chimney basics

[dug]

I am in the process of figuring out how to install my wood stove and would appreciate some advice on pipe and chimney components.

As I understand it you need a triple wall stainless pipe to pass through the roof. How far below, and above the roof should this extend? Is this a single piece that goes from the stove pipe to chimney cap? My roof pitch is 12/12 and I plan on running the chimney through a foot or so  from the peak of the roof.

My ceiling is a cathedral and I have seen through the roof kits specifically made for those that are box shaped. Is this necessary? Will other systems work?

I plan on using single wall pipe because of price and better heat radiation, though I hear it doesn't last as long. Bad idea?

Cost is a major factor for us but safety is the most important thing.

[MountainDon]

When it comes to the chimney above the roof, a picture is worth a thousand words...



so if your chimney is close to the peak you want 2 feet above the peak. Or more.

more coming...

[MountainDon]

From the ceiling up you want Class A pipe. This can be triple wall with air chambers or double wall filled with mineral wool. There are many brands. As long as they are Class A they pass the same tests. The metal inside and outside should be stainless steel for longest life. Stick with one brand, same series as they do not interconnect properly if at all.


With a cathedral chimney you have two choices.

Use a cathedral ceiling specific chimney mount. These attach to the insulated pipe and to the rafters. They adjust for angle.

Frame in a box similar to what I did with our gazebo. That permits using a standard flat ceiling mount.

I used the box method as that allowed me to use a standard kit off the shelf from Lowe's. At $160 or so it included the mount, ceiling trim, attic insulation shield, roof flashing and chimney hat. A bargain.

Single wall black pipe should be kept 18 inches or more from any combustibles. That's why you will see a short length of insulated pipe dropping from the ceiling mount, before transitioning to black pipe.


True, the longer the run of black single wall pipe the more heat that will be radiated to the living space. With the chimney running cooler there may be more condensate leading to more creosote in the chimney pipe. So I see it as a trade off. More insulated pipe dropping from the ceiling down costs more though. Another trade off. In our case any extra heat from the black pipe is not usually needed as the stove can radiate more than enough heat itself.

I chose Selkirk brand, double wall mineral wool insulated, as that was what Lowe's had with their good price. They make 12, 18, 24, 36 and 72 inch lengths, IIRC.

If trying to save money, do not use galvanized pipe even if it is free. At high temperatures zinc may be gassed off and that is very bad to breath.


I used a telescoping pipe to connect the stove to the ceiling. It is welded pipe and heavier wall than most snap seam pipe. Looks better too. It makes it very easy to make the connection to the stove; no tilting the stove trying to slip the pipe in place. It also makes cleaning easy. I remove the screws that secure the pipe to the stove and slide the pipe up, the lower section telescoping up over the upper section. hen I attach a heavy bag to the pipe, go up on the roof and run the brush down the pipe. All the crud collects in the bag.


Cost is important, but safety is number 1. I don't know if you saw the notes on low temperature charring of wood and the fire danger it presents. It was in another thread recently. The Kentucky A-frame thread. There are also older threads on that but I haven't searched very hard for them.

[dug]

Great info Don- many thanks.

The only thing I am still unsure of is the class A pipe through the roof.

If I go through the roof a foot from the peak, the chimney would need to be at least 3 ft. off the roof. Does the class A pipe go the top, or just need to go 18 in. below, and above the roof. I am guessing you run it all the way but since it seems to be one of the more expensive parts I thought I'd ask.

Thanks!

[MountainDon]

Class A all the way from below the ceiling, through the ceiling (and attic where there is one) and out through the roof all the way to the chimney cap. The chimney parts should all come with instructions but I believe it is normal to keep the class A pipe a minimum of 2" from any combustibles. As well any insulation material in the ceiling or attic is also kept 2" away from the class A pipe.

When I was shopping I downloaded instructions from the manufacturer's website and read up on what was required before buying anything.

[Shawn B]

Dug,  Never convert back to single wall pipe once you have started running class A (or class B for gas fired appliances). I wanted to add that for those needing
class A pipe, but where the pipe is inside an attic, or chase, some manufactures make class a pipe with the outer cover in gray galvanized, the inner liner is stainless steel, so no need to worry about off-gasing. This will help reduce cost some. Also I have seen black class A pipe.

[considerations]

Like Don I used Selkirk brand Class A, double wall mineral wool insulated, and used a telescoping pipe to connect the stove to the ceiling of welded pipe. The Class A goes all the way from below the ceiling, through the cathedral ceiling and out through the roof all the way to the chimney cap which is 3 feet higher than the ridge. That telescoping pipe is going to come in handy, as Mountain Don noted because I talked a chimney sweep into cleaning it the same way Don described. He didn't want to get up on the roof.   I'm considering some sort of permanent ship's ladder type arrangement at a future date.

Also, I used a big orange (nasty color) silicon boot on the roof for the chimney to come through. The boot had a flexible, (maybe lead) edge around it that allowed it to conform to the ridges in the metal roof.  There is a lot of sealant involved and a storm collar above the boot as well.  So far so good, no leaks, but I've see nicer jobs.

I could not find a pre-fabbed box for inside the ceiling that matched the 12/12 pitch so I had to build one out of galv sheet metal, and stuffed rock wool insulation around the part of the chimney that went through the box.

[MountainDon]

Also, I used a big orange (nasty color) silicon boot on the roof for the chimney to come through. The boot had a flexible, (maybe lead) edge around it that allowed it to conform to the ridges in the metal roof.  There is a lot of sealant involved and a storm collar above the boot as well.  So far so good, no leaks, but I've see nicer jobs.

I was lucky I guess, as I was able to get a gray colored boot, the brand name escapes me right now. Likely very much the same as yours, considerations. The lip that goes down on the roofing has the silicone molded over an aluminum alloy, "dead soft aluminum". We formed the lip to the contours of the roof ribbing as best as we could, then used 100% silicone caulk to seal the joint to the roof. Tighten the screws just enough. The boot never leaked at all. It sort of goes against all the roof flashing rules we've heard in that there is no overlap of the metal and boot. But done carefully it works. The roofer that did out house roof said he prefers to use these on metal roofs but on a modern house with plenty of vent stacks they can add up to a lot of $$ in a short time.

I like it because it is very easy to add after the metal roof is done. Available in many sizes.

If/when the name pops up I'll post it.  It's in my topic someplace....  

[dug]

Still trying to figure out my chimney install. I have a few unanswered questions and thought I'd "vent"  some of my frustrations as well.

I am the type who would rather shop local if possible. I don't mind paying a bit more as the expert one on one advice is worth it to me, and I like to support the local economy. So yesterday I visited the local wood stove store to inquire about chimney pipe. The owner pointed me to the chimney section and started walking away. I informed him I had some questions and so he grudgingly turned around.

After explaining the circumstances of my install he showed me some of the components I would need, including the ceiling support box. I told him what the roof pitch and rafter depth was and asked him if I would need the 24 in. or 36 in. box. "The 24 in. would probably work, but you might need the 36 in."   ? Never did find out which one.

I asked for a price of all the components necessary and he began rattling off the numbers of each individual part, I had to interrupt to say I wanted the total cost. Audible sigh from owner  . I'm thinking "you got something better to do?" (I was the only person in the store)  He then got out his price book and wrote down prices of the individual parts and handed it to me. "Uh, how much am I looking at" I asked him. "About $700" was his reply. I told him I was looking for a number that was a little more concrete and asked to borrow his calculator. After adding up the parts I came up with $897 including tax. "Does that sound about right?" I asked. "I guess" he replied.

Hope he goes out of business real soon.

So my question is this- Does the top part of the square ceiling support box get cut to match the roof line? Or installed as is and left square? I would think it would be cut so the box encloses the chimney entirely, but have not been able to find an answer.

What size support box should I get? Roof is 12/12 and rafters are 10 in. I understand that single wall stove pipe should have 18 in. clearance from combustibles but have never seen one of these boxes that appear to hang that low below the ceiling. If this is true that would mean the high side would extend 30 in. below the ceiling. Grumpy store owner said a few inches is good.

Any special accommodations I should make to allow for easier cleaning of the chimney? I have a Vermont Castings Aspen stove.

[davidj]

So my question is this- Does the top part of the square ceiling support box get cut to match the roof line? Or installed as is and left square? I would think it would be cut so the box encloses the chimney entirely, but have not been able to find an answer.

My support boxis left square, leaving a bunch of space above the box that's basically open.  Both the roofing contractor and the insulation contractor managed to end up with combustible material touching the chimney in that section (it's insulated, but I think it still needs 2" clearance to combustibles).  I think I'm gonna box it off with plywood before putting the insulation back in.

What size support box should I get? Roof is 12/12 and rafters are 10 in. I understand that single wall stove pipe should have 18 in. clearance from combustibles but have never seen one of these boxes that appear to hang that low below the ceiling. If this is true that would mean the high side would extend 30 in. below the ceiling. Grumpy store owner said a few inches is good.

Isn't the normal way to do a length of triple wall/insulated chimney under the support box?

[Jeff922]

Dug, my chimney installation on a 12:12 roof required two sections (3'?) abore the roofline.  I've installed two chimeys.  Both time I've used Simpson products (DuraPlus Triple-wall chimney with Duravent DVL double wall stovepipe).  I really like telescoping stovepipe.  When I sweep the chimney, I just undo a couple of screws and slide the chimney up above the stove a little.  Then I can tape a plastic bag to the bottom and sweep the debris right into the bag.  But I was a little less than satisfied with the Simpson stuff last time.  Instructions were terrible, missing some screws, and the newer style chimney cap doesn't appear to just twist off easy like my old one.  Next time I'll try a different brand.

[dug]

Isn't the normal way to do a length of triple wall/insulated chimney under the support box?

Every source I have researched says standard single or double wall stove pipe connects to the bottom of the box, then class A chimney goes from the bottom of the box to top of exterior chimney, but I am still not really convinced.

My support boxis left square, leaving a bunch of space above the box that's basically open.  Both the roofing contractor and the insulation contractor managed to end up with combustible material touching the chimney in that section (it's insulated, but I think it still needs 2" clearance to combustibles).  I think I'm gonna box it off with plywood before putting the insulation back in.

I could do that, but I wonder if you could, or should cut the metal support box to fit the roof slope?

I really like telescoping stovepipe.  When I sweep the chimney, I just undo a couple of screws and slide the chimney up above the stove a little.

Thanks for the tip, for some reason I was thinking of connecting the telescoping part to the to the ceiling  connection but that makes a lot more sense.

[MountainDon]

I've never used a store bought box for a sloped ceiling. I have built a couple of 2x4 framed boxes for sloped/cathedral ceilings and used a regular flat ceiling mount kit.  Therefore I have no idea on that, other than to download the manufacturers installation guide.

I've used nothing but Selkirk since my first chimney installation  in 1979. (Partly because back then they were made in the city where we lived.) Selkirk has an online chimney planner. http://www.selkirkcorp.com/installation-planners/supervent-2100.aspx  Maybe that will help. They also have complete online catalogs available. The planner is not perfect; it does not list things like the clamp bands to use where one section of insulated pipe interfaces with another insulated section.

They also have all their installation manuals online.


A section of insulated pipe can be readily attached under the ceiling mount/trim instead of placing the insulated to black pipe adapter right there. The most important thing is to measure and add whatever insulated pipe length is needed to keep the black pipe 18" or more from any combustibles. The adapter is then mounted to the bottom end of the insulated pipe.


The telescoping pipe should attach at the lower end of the inside black pipe and then to the stove.

[Shawn B]

Every source I have researched says standard single or double wall stove pipe connects to the bottom of the box, then class A chimney goes from the bottom of the box to top of exterior chimney, but I am still not really convinced.

Dug. your confusing yourself on the pipe I believe.  Double wall pipe (uninsulated) is known as Class B venting or commonly referred to as B Vent. It is not rated for wood burning (solid fuel, or oil) because of the temperatures involved. If your talking double wall insulated pipe that is Class A pipe.

As Mountain Don said you can run single wall black pipe up to the ceiling box or stub some Class A pipe bellow. The choice is mainly decorative. The 18" clearance for single wall pipe is measured straight out from the sides around the pipe.  Remember the ceiling box will act as a heat shield somewhat.

Last winter I helped install a ceiling box on a 10/12 pitch roof. We set the low side of the box at 4"-6". Because the box was taller than we needed it was cut to match the roof angle. This also allows more fasteners to be used to secure the box. Remember the ceiling box will be holding 99% of the chimney weight from the box up. Hope this helps.

[JRR]

I've always thought these folks were a good resource; however, now the website is under a bit of "reconstruction":
http://www.elmerspipe.com/

[dug]

I've never used a store bought box for a sloped ceiling. I have built a couple of 2x4 framed boxes for sloped/cathedral ceilings and used a regular flat ceiling mount kit.  Therefore I have no idea on that, other than to download the manufacturers installation guide.

I was under the false impression that the metal box should enclose the class A pipe through the ceiling. After reading your post I thought about building the support box but it would have only saved me about $60 and I kind of prefer the look of the metal.

Dug. your confusing yourself on the pipe I believe.

Wouldn't be the first time.     I do understand the difference between the class A chimney and class B vent pipe but may have failed to properly convey that in this post.

I ordered everything I needed for my chimney yesterday. I went with Northline express, they were very helpful and friendly and the total came out to $665, over 30% less than the exact same  product available locally (Simpson Dura-Vent). Sad to me that an online company would offer better, more knowledgeable service than the local mom & pop store.

As with every phase of building so far I have learned a lot and appreciate everyone helping me walk through this process.

[considerations]

"I went with Northline express, they were very helpful and friendly"

I agree, plus they always seemed to have the odd part I thought I needed.   Very professional.

[smoked out]

MtnDon, my pipe is the other way. the top slides down over the bottom. It was installed by professionals but I I think they screwed up. It started smoking at the ceiling. Since the top pipe is the larger one it doesn't go INTO the ceiling support and is about 1/8" from it. They put a strap over it there. They are now telling me that smoke always leaks out of the stovepipe but if it's real bad it must be the fault of the chimney sweep. In light of the fact that there are screw holes, a chimney sweep can't possibly put it back together wrong. Was sick for months & then saw the smoke & had the chimney cleaned. 3 months of burning at med to hot temps & there was so much creosote there was only about an inch of airspace. This has to be because of a leak. So my question is, should the pipe go into the ceiling support? Also the top of the top pipe is the crimped end. Is this right? Not for nothing but I think if the fatter pipe is on the bottom, like yours, wouldn't smoke leak out at the connection Thanks Laura   PS DUG - my small town is the same. I've decided that shopping local is my last resort.

[Dave Sparks]

I would add the importance of having a nice long chimney to the list of smart things to do to have an excellent woodstove. Good draft keeps the smoke out during firestarts and also keeps the creosote down. One of the advantages of a steep high pitch roof is it forces a long stovepipe. I have direct experience with quite a few and if hardwood is burned exclusively, the chimney inspection just verifies that the system is clean and nothing is required.

[Squirl]

Laura,

Smoke should not be leaking out.  From my reading there are sealing cements that can be used.
A good article to read is the diy wood stove safety guide at mother earth news.  It is from 1980, but many of the same rules apply.
http://www.motherearthnews.com/Do-It-Yourself/1980-01-01/Wood-Stove-Safety.aspx?page=2
According to the article it was mildly debated at the time which end should be the male and which end the female connection.  I still find articles back and forth over which end is up and which is down.  Most though state that the male end (the end inserted in the other) should be down. So from the chimney each section fits into the section underneath it.

I'm not totally sure how your pipe is connected from your description.  Normally the Triple wall pipe that is running through the support box connects to the black wall pipe through a chimney adapter.



The leak may have had an effect by letting in too much air and cooling the gases too much.  That much build up is more likely factors of burn temperature, type of wood, and draft.

[Alan Gage]

Where are you measuring your temperature? Stove top or pipe above the stove. If pipe above the stove is it a magnetic (external) or internal probe? If on the pipe how high up? And maybe I missed it, but what's your stove?

So what are your temps once the stove is cruising along? Any visible smoke from the chimney?

I've always heard male end of pipe goes down. Reason being so that anything running down the chimney internally stays internal.

I agree there should be no gaps where the pipes connect but even then I'm a bit surprised you're getting much smoke leaking out. If the chimney has good draft it should be pulling air in through any gaps.

I have a Selkirk chimney. All their install instructions are on the website.

Alan

[John Raabe]

The crimped end of single wall black pipe should be installed downward so that moisture stays inside as it drains and will not leak to the outside of the pipe.

While you might have a small amount of smoke when first starting a fire in a cold chimney, you should not have smoking once the pipe is warmed up and the draft is working.

Here is info on how to post images in a thread: http://countryplans.com/smf/index.php?topic=3512.0

IS YOUR POST GONE? In cleaning up this thread I may have deleted a post on this page. If it was yours, I have I apologize - it was not a problem with the post - only my mis-clicked delete button. Please repost.

[smoked out]

Finally found the PDF instructions for my ICC pipe. It's in right. I have a Kuma Tamarack. I keep the thermometer on the vertical (ish) surface. Called Kuma & he said to put it there, to load up, bring it to 700 or 800 & then shut down completely. I hadn't been getting it that hot.
The smoke was due to a clogged chimney. Kuma says that's what will happen if I don't burn the way they say. What I'm trying to determine is why it clogged in 2 1/2 months this year when I'm burning hotter with dry wood finally.
Last year was wet wood, low burn. Cruising temp around 350 & when it got colder, 400... if I could get it that hot. Wood ran low in mid March & I only burned once a week or so. One day, cold stove, wet wood, couldn't get it to stay lit unless the door was cracked. Got it going & the chimney sounded weird. Looked outside & the creosote on the chimney was orange & snap, crackle, popping... so I shut down. Could the reason the chimney was cleaner this summer, after burning wet wood from Oct to March, was that it self cleaned that night???
The only other difference between last year & this year is that many pieces of the Doug Fir this year were covered with lots of pitch. Some looked like one side was painted with wax. Could that make such a huge difference in creosote
We're talking 6 months of wet wood/low burn vs. 2 1/2 months this year of dry wood higher temps (cruising at 425) ... resulting in the chimney clogged to within an inch of it's life. Thanks for any input.

[Alan Gage]

I guess I don't quite know what you mean by placing the thermometer on the "verticalish" surface. I looked at a picture of your stove and I see the top isn't flat. Do you mean the thermometer is on the sloped portion of the stove top.

If so 800 degrees is VERY high for a stove top, I'm surprised you could even get it that hot.

What does the fire look like after you shut down the air? Good secondary burn? Are you seeing smoke from the chimney (outside)?

How long has the wood been split and stacked?

Alan

[Squirl]

It sounds like the wood is different between this year and last.  The hot burn is good, but when you "shut it down" do you close all air off completely?  With an air tight stove and lots of fuel this will cool the fire and gas to create lots of creosote.  The longer the burn after you close off the air the more the creosote.  This chemical reaction is known as pyrolysis. There are always tradeoffs in wood burning of energy efficiency vs. convenience.

Creosote is the name given to many different types of tars and volatile organic compounds that are given off when burning wood.  Softwood species usually have a higher content of these tars than hardwoods.  The pitch you described is high in tar compounds.  In the old days people used to create stills and heat wood without oxygen (pyrolysis) to get products like tar, pitch, and methanol.