Stovepipe/Chimney for a masonry heater in a yurt

[hierony]

I live in a 20 ft diameter traditional-style yurt. Given that I don't have terribly much insulation plus yurts are relatively light structures with little mass & on the draftier side, I'm making a masonry heater to keep things warm (esp. overnight & while away at work). A professional stove mason draw up the plans so I can do the work myself--total cost is likely $1-2k. For heater pictures, see my yurtforum album.

The firebrick core is done & I'm starting on the facing, but I'd like input/review for the stovepipe/chimney setup. I've a technical/science background, but I lack in the wood-burning experience department--there are a number of practical details I don't know/may have overlooked. Being a traditional yurt, everything is 'temporary' & most building codes don't apply--but I want to be safe & reasonable. Reading this forum has been great!

Anyhow, the details/ideas:

The heater is in the center of yurt--stovepipe center is offset by ~7.5" from yurt center. The stove mason recommended 6" stovepipe; a small section will be embedded in the top of the heater (with a damper to prevent heat loss after fire is out). The crown ring where the stovepipe will exit is 4-4.5 ft above the heater--the ring itself is about 5 ft in diameter, with wood lathe to form a dome. There is a square piece of canvas that covers the crown ring (it will be shifted away from the portion with the stovepipe).

So my idea/current plan: single-wall 6" stovepipe all the way up & out (~7.5 ft total to get 3 ft above roof exit). Use a high-temp silicone pipe flashing on a sheet of metal glued to a separate 'chimney' canvas section to hold the stovepipe, with the section of stovepipe near the crown ring/silicone within a 7 or 8" stovepipe section to make it double walled. I will have to modify/cut the crown ring lathe to make clearance for the stovepipe. See attached pictures.

My questions:

Will cheap farm/hardware store snapping 24 gauge stovepipe work well, or is welded stovepipe better? Will the snapping stuff leak or require the seam to be sealed?
Black stovepipe or galvanized (inside &/or outside)--aesthetics or other differences?
Best way to make 'double-walled' pipe-- 7" or 8" outer pipe? perlite w/ cement binder, use leftover 2012 F-rated Superwool blanket, or just air gap?
Can I tee in a tiny wood cookstove near the masonry heater so I only need one chimney?

 

[bholler]

Just buy some stainless class a chimney sections you dont need much so it wont be a huge cost and it will be much safer. And we need to see some drawings of what you are planning for the roof penetration because it sounds pretty scary from your description. But if we saw drawings it may be fine. pretty much you need to make sure you maintain proper clearances. Which for class a would be 2". There is no set clearance for your fabricated double wall but I guess you could consider it a shielded single wall which would be 6".

 

[Woody Stover]

@begreen might be the resident yurt guru...

 

[Woody Stover]

I wouldn't use galvanized anywhere in the system, I think it can off-gas.

 

[hierony]

I looked at threads where Begreen & Bellingham Chimney Sweep commented/posted. It looked like they both have done/advised wall-exit yurt chimney systems, whereas I'm trying to go through the crown ring. Similar problems though--maybe I should try adapting one of the Rainier/Pacific/Colorado yurt stove kits to my crown ring lathe?

I'll make up a sketch with the different details & all my numbers when I get some time.

The Class A chimney is expensive, plus there's the stovepipe-to-chimney adapter/thimble that I don't have normal framing to support. From what I've read, Class A is basically stainless pipe in a double wall setup, either ceramic/mineral wool filled or with an air-gap, with fancy locking connectors. In other words, you should be able to make your own minus the fancy connectors.

Re: galvanized--the fellow that sold me the cut 2 ft section asked if the stovepipe would be exposed, but didn't specify what he meant (I was thinking exposed to the elements, not exposed to the room/yurt/people). There's one or two threads on the forum mentioning zinc outgassing, but if you google welding galvie you'll hear more about metal fume poisoning (temporary, & tolerance built up). The best argument I've heard there is that zinc often contains a small amount of cadmium as an impurity, which is much more problematic (I knew a machinist that wouldn't weld/braze galvanized parts).

 

[begreen]

We did a wall-exit chimney for the yurt for a few reasons. It moved the stove off to the side which the owner desired. It allowed more chimney height with good strong support and it ensured a good leak free installation.

For this installation the location is established so the main issues are safety and support. The chimney is infrastructure and quite important. Here is one option that solves both issues. Bolt a chimney anchor plate to the top of the heater. That will solve the support issue. Then go all the way up with chimney pipe. This will provide a strong, safe installation. You can use galvanized chimney pipe (galvalume). Only its exterior is galvanized, its stainless inside and will save some bucks. It will last at least 10 years in your dry climate if not more. Be sure to have a screen on the chimney cap. A friend had their army tent catch fire from embers coming out of the cap.
An anchor plate looks like this:

(broken link removed to http://www.woodstovepro.com/store/Chimney-Pipe-Venting-Pipe/Wood-All-Fuel-Piping/6-inch/DuraTech/M-G-DuraVent-6-DuraTech-Anchor-Plate-9441-6DT-AP-p14927.html)
Here is a supplier of chimney at a good price.
(broken link removed to http://www.woodstovepro.com/store/Chimney-Pipe-Venting-Pipe/Wood-All-Fuel-Piping/6-inch/DuraTech/M-G-DuraVent-6-x-48-DuraTech-Chimney-Pipe-Galvalume-9407GA-6DT-48-p14882.html)

 

[bholler]

The Class A chimney is expensive, plus there's the stovepipe-to-chimney adapter/thimble that I don't have normal framing to support. From what I've read, Class A is basically stainless pipe in a double wall setup, either ceramic/mineral wool filled or with an air-gap, with fancy locking connectors. In other words, you should be able to make your own minus the fancy connectors.

I would mount the class a right to the top of your heater and run up from there nothing else needed. And yes it is double wal with insulation in. And it has been tested to work correctly with specific clearances. What ever you make will not be the same and there is no way to know what the required clearances would need to be.

Re: galvanized--the fellow that sold me the cut 2 ft section asked if the stovepipe would be exposed, but didn't specify what he meant (I was thinking exposed to the elements, not exposed to the room/yurt/people). There's one or two threads on the forum mentioning zinc outgassing, but if you google welding galvie you'll hear more about metal fume poisoning (temporary, & tolerance built up). The best argument I've heard there is that zinc often contains a small amount of cadmium as an impurity, which is much more problematic (I knew a machinist that wouldn't weld/braze galvanized parts).

You cant use galvanized on a wood stove it is unsafe. And besides it wont last long under the conditions you will be subjecting it to. You need stainless plain and simple My wife's family are all welders and believe me welding galvanized can over time be very very bad for you.


I understand you want to do this cheaply but really you are talking about what 2 4' sections of pipe? So a couple hundred bucks. You will some money in your pipe and a fair amount in the insulation. And the worst part is you will be lucky if it lasts more that one year. So in a couple years you would have the correct pipe paid for.

 

[byQ]

I just built a masonry heater and had to deal with the chimney question. I knew how to build the heater but the masons' never talk about how to build the chimneys. Like bholler said double walled is a good option. I bet you you could find some used/new stove pipe at a reduced price because you don't need much.

Someone with less than what is needed for a house is going to have to sell it at a reduced price. And 7" pipe can be had cheaply because it is an odd size for traditional wood appliances, like wood stoves. It would work fine with your masonry heater.

In my case, like you, my build cost was in the $1000-2000 range. I compared prices/availability and decided to go with 8"x 8"x 16" clay flues. They cost about $9 each. I stacked them with mortar and used a silicone to seal seams. Code says 1/2" air gap if I surround with brick. I have some old brick so I surrounded the clay flue leaving the air gap. I covered the brick with the stone I was using for the outside (so you can't see it in the 1st picture). I just noticed we are both in Idaho.

 

[hierony]

I appreciate all of your input. It took me a little bit to review & figure out how I want to proceed. See the attached sketch of what I was planning on--it should give you all a better idea since my written description wasn't adequate. Per the stove mason's instructions, the stovepipe will be anchored/mortared ~6" into the masonry heater (a good ton or so of material) and then kept from swiveling by the triangular piece of canvas at the crown ring level--should be quite sturdy with zero degrees of freedom once everything is screwed together/tied down. This is very similar to the yurt wall exit setups (see Colorado Yurt's page), just vertical.

It seems no one wanted to comment on snaplock vs welded seams on stovepipe or sharing the chimney with the mini wood cook stove (only one flue actually open at a time/not used simultaneously).

byQ--I really liked your heater build thread. From the pictures, I'm guessing you're more towards southern/eastern Idaho--I'm a bit more north in the Palouse region (a bit rainy sometimes). I'd be very interested to hear how your heater ends up working for you. I hope you didn't use the wet/water-soluble refractory mortar while it's just sitting out there exposed...

Re: Clearances. I dug into the code. UL won't tell you their testing procedure unless you pay $500. The (broken link removed to http://premiumaccess.iccsafe.org/document/code/287/4963347), table 803.10.4 has an interesting description of System D (2" clearance)--use a 1" gap filled with insulation between two pipes at least 24 gauge. In other words, if I put an 8" stovepipe outside my main 6" stovepipe & fill the gap between them with ceramic paper/felt/wool insulation (I have a _lot_ left over from the heater core build), I can expect to have a reasonably safe system. Mind you, this is _not_ factory built, this is _not_ UL tested, this will _not_ pass inspection, this will _not_ qualify for insurance.

Cost wise, the stovepipe & everything will probably be about $100 new. If I went with Class A it would likely be $500 or more (need shutoff damper, chimney cap, etc), plus the heater-to-chimney seal would have to be redesigned and I wouldn't be able to tie in the cook stove. I'd like to be able to disassemble things when I move, so I prefer metal pipe over clay tile. Given that there will only be one or two firings a day, a masonry heater burns very clean, and most of the heat will be absorbed by the mass, any claim that the stovepipe will wear out in a year is a bit loufoque.

 

[bholler]

Given that there will only be one or two firings a day, a masonry heater burns very clean, and most of the heat will be absorbed by the mass, any claim that the stovepipe will wear out in a year is a bit loufoque.

I am sorry but it is going to wear out in at most 2 seasons but I would expect one. And yes allot of the heat will be absorbed but the exhaust temps will still be fairly high. I have seen allot of stove pipe that people have tried to use as a chimney and it never lasts. So you will be paying that $100 every year or 2 so it will quickly add up to the cost of class a chimney. Is the pipe you buried in the heater at least stainless? You will also have to disassemble it to inspect that inner pipe every year because if it fails you will them be letting the exhaust get into that insulation which can be extremely dangerous.

 

[hierony]

Hmm, I may be looking at this from the wrong side--the inside of the pipe may be alright (baring excessive condensation), but the outside of the pipe may deteriorate quickly due to weather. The stove mason said the exhaust temps could get up to 400F if it gets fired hard/long (ie, too much). @bholler, your profile says you're a chimney sweep--how many times have you seen stovepipe used as chimney? How bad was it?

I am thinking stainless may be the way to go, at least for the portions outside. Most stove pipe doesn't have any alloy listed, so I'm going to guess it's not terribly rust resistant. The other method that comes to mind is painting the exterior portions with something durable.

 

[bholler]

your profile says you're a chimney sweep--how many times have you seen stovepipe used as chimney? How bad was it?

Read my post above. You do know that the byproducts of burning wood are pretty corrosive as well right? It will not last long at all.

 

[begreen]

Stove pipe is not permissible as a chimney. Most sweeps would want it changed before they took any liability for working on the flue.

 

[bholler]

Most sweeps would want it changed before they took any liability for working on the flue.

Yes I said I have seen it I did not say I worked on it.

 

[begreen]

I'll bet you have seen some real winners over the years. Have any pictures?

 

[bholler]

I'll bet you have seen some real winners over the years. Have any pictures?

A few I could dig out I am sure

 

[begreen]

I only have a couple that have shown up with attempts to use single-wall for chimney.

 

[byQ]

Would some pipe like this work? You say 7.5'. There are three 3' sections and a little more.



Chimney pipe "Duravent" for wood stove-$250(Benton City)hide this posting
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© craigslist - Map data ©OpenStreetMap
58607 N River Rd
(google map)

condition:excellent
make / manufacturer:Simpson
model name / number:Duravent 90127
size / dimensions:36" x 6" x 10" + gas vents

Simpson Duravent 9017, 6" triple-wall stainless insulated woodstove chimney vent pipe, 36" sections, NEW IN BOX, have 3 of these for sale. Also have a 36" section and a wall-vent section (24" with 90 degree fitting) for propane exhaust venting (used, came from a free-standing gas stove), these are 4" inside diameter X 6" outside diameter double wall (outer wall for intake air). Want to get rid of all at once please, no partial sales. Compare prices at $130 ea plus shipping/tax for the 9017, $120 for the various sections on the gas pipe. That's about $600 if you ordered new stovepipe now. PRICED TO SELL QUICKLY, BEST OFFER AFTER 2 WEEKS OF POSTING WILL BE ACCEPTED

 

[hierony]

Now that's a good find! Tomorrow I will have to see if the fellow will ship the DuraPlus stuff. Mind you, that 6" triple-wall is 10" OD. I would just need a rain cap & a way to connect to the 12" section of 22 ga Excel Prime I embedded in the refractory.

 

[hierony]

Hmm. It looks like the local HomeDepot has 6" DuraPlus bits: $98 for stainless 3 ft, $57 for the rain cap, and $31 for the stove/chimney adapter.

DuraVent also has some interesting details on their (broken link removed to http://www.duravent.com/InternetSalesPolicy.aspx): "DuraVent has identified products that may be suitable for a non-certified installer who has above average strength, aptitude and skills for doing a complex installation such as an all-fuel chimney system. These product categories are made available to consumers and do-it-yourself installers, including Internet Sales, and will be fully warranted: DuraPlus; PelletVent; PelletVent for multi-fuel; DuraBlack; DVL; and Type B gas vent."

Whereas the DuraTech (6" ID, 8" OD, 2" to combustibles) is dealer/professional install only.

 

[hierony]

So I went over my design & realized that it used the absolute minimum pipe height. Upon consulting with the Stove Master, I realized I ought to have flexibility in chimney height in case of insufficient draft--not an easy feature for a home-built setup. Plus, the cost of good stainless pipe (24/22ga welded-seam 6" & 8"; generally available as chimney liner) to make double-wall would have put the total cost near that of factory-made Class A. I checked out the horribly organized local hardware store chimney pipe (Selkirk) & realized it was below typical internet prices I'd seen, plus I'd be able to easily extend it if needed. Minimal driving/no shipping required.

This is what I ended up with:
$17 spark arrestor
$51 cap
$165 4 ft Class A
$105 3 ft Class A
$50 roof support kit (attachment to 2x4 frame in crown ring for ~50 lbs chimney pipe)
$35 stovepipe adapter
$90 in 2-3 ft of 22ga welded seam stovepipe & tee

 

[velvetfoot]

I saw a movie yesterday: "The Eagle Huntress". They lived in a yurt and had a small metal stove of some sort for cooking with a good length of chimney pipe. They broke the yurt down for the winter and moved to a more substantial house. Aren't these things made to be broken down and moved? Do they stand up to the snow? What's the point in Idaho? I think the people in the movie moved in the summer for the grazing for their animals.

Edit: Is it some kind of tax thing?

 

[hierony]

Depending on the design type, a yurt can handle snow well--temperature swings are somewhat tricky. The traditional style yurts breakdown very easily (matter of hours), whereas the modern yurts take a day or two. The general point of my yurt is to actually own my home (no debt where you end up paying 2x the actual value) and take it with me as I move. Plus avoid outrageous rentals ($500/month cheapside). Right now I don't own property (it's in the 5 year plan), but I'm only paying $120/month for rent (~1/4 acre, water & electricity included, 25 min to work/town)--roughly on par with typical annual property taxes...

If you're interested in yurts, feel free to check out the (broken link removed).