Newbie question re chimney height

[ChillyNoMore]

Hi again,

I'm still working out the details to get my Scan 61 installed (hopefully before winter is over). Now I am trying to determine the right height for the chimney...

The Scan manual is a bit confusing on this topic. First it says: "The chimney must extend 3 feet above the level of roof penetration and a minimum of 2 feet higher than any roof surface within 10 feet." I understand that this is the code minimum and for my low-pitch roof (2:12) it translates to ~4' of Class A. The stove itself is 3' tall and will be installed on the main floor which has 8' ceilings. So if I follow the minimum recommendation, I would have a total system height of ~12'.

Then the Scan manual goes on to say: "The condition of the chimney and height is very important; we suggest a total minimum height of 15’. Measured From the floor level on which the stove is installed." If my basic math skills are any good, that would mean 7' of Class A chimney above the roof.

When I consulted the folks at the stove store, they recommended starting on the short side (5') and adding pipe if necessary down the road. Is this good advice? I don't want to short-sheet the install and then struggle to get a fire lit (especially since I'm a new wood burner). At the same time, I don't want to end up with a very tall (and very expensive) chimney and too much draft that I have to damper down. (The same guy at the stove store recommended that I get the stove pipe adapter with the damper. Was he upselling me or giving me good guidance?)

A few other things you might want to know about the install:
- the house is a 1960's ranch, with low cathedral ceilings (the ceiling is the roof, there is no attic)
- I'm located in the Columbia River Gorge so the winds can really rip
- I'll be installing a VacuStack chimney cap in order to avoid downdraft problems

Thanks in advance for sharing your wisdom! It is giving me ever more confidence as I attempt to wean myself off fossil fuels.

 

[Nic36]

I would take the advice and only have 5 feet above the roof for the simple reason that any more than 5 feet and you will have to brace the chimney. Try 5 feet and see how the stove drafts. If it does not pull a good enough draft, you can add another 2 or 3 feet and see what happens. It is easy to add another section. But, as I said, once you go over 5 feet you have to brace it. Still not a big deal. I braced mine.

I don't see a need for the damper if the stove already has an air control. You can also add another one of those later if need be.

Just my $.02 worth.

 

[Backwoods Savage]

I agree to start a bit short. Many times it will work out but if not, it is very simple to add more height. Our chimney is short but we do fine with it.

You will also find that the fuel has much to do with how that stove will heat. You might very well end up thinking you need more chimney when in fact you just need better wood. Burn no wood before its time.

 

[begreen]

This is going to be interesting. I would plan on a roof brace for the stack anyway. Columbia Gorge winds are really strong and persistent. The wind can blow all day long at 70mph there. Windsurfers love it. I once clocked them going 60mph on the river. Quite a rush.

 

[regency]

My 6'' SS liner/chimney is also only 12ft. It burns great and the short chimney makes for virtually no build up!

 

[cre73]

I am a couple feet short of the recommended for my stove and have no issues. Start short and if needed add some until you are comfortable with the draft. Next thing is don't worry if the draft isn't the greatest on your first fire, you need to give it time to warm things up.

 

[LLigetfa]

The flue will be in a tug-of-war with the building, so how well the building is balanced will determine whether you can get away with a shorter flue. You also didn't mention whether it will be a straight up install or if there will be any elbows/Tees.

Since the flue will only be supported at one point, namely a cathedral support, it really should be braced.

 

[Troutchaser]

I'm adding an extra 3ft. of exterior as soon as I can get on the roof (snow right now).
I'm not happy with the smell I constantly get standing on the porch. Also, I seem to be having trouble with keeping the strong draft going after burning for 3 or 4 hours hard. We get a stink in the house that I'm only guessing is the stove throwing off gases because the short flue can no longer suck them out fast enough. It's a pressure issue I'm guessing, but I figure a little more pipe can suck harder and help out with that.

 

[LLigetfa]

I'm adding an extra 3ft. of exterior as soon as I can get on the roof (snow right now).
I'm not happy with the smell I constantly get standing on the porch. Also, I seem to be having trouble with keeping the strong draft going after burning for 3 or 4 hours hard. We get a stink in the house that I'm only guessing is the stove throwing off gases because the short flue can no longer suck them out fast enough. It's a pressure issue I'm guessing, but I figure a little more pipe can suck harder and help out with that.

While a taller flue could help in the tug-of-war and also keep the plume away from the building envelope, you would be better off addressing the balance issue. Seal where warm air leaks out, provide more makeup air, and consider installing an OAK if you don't have one.

 

[Troutchaser]

LLigetfa, we have a 23' cathedral, wood siding. I do imagine I lose the heat out the top of that and elsewhere, but sealing up would be a nightmare. Make up air might be more practical.
What is an OAK? Sorry, I'm new at this.

Question? If the house is wanting to draw air in,why would the warm air still escape? Wouldn't those cracks be sucking in instead of letting out?

 

[cre73]

OAK. Stands for "Outside Air kit". Pretty much is tube supply air to your stove from outside. Usually used in airtight homes.

 

[oilstinks]

I am short on pipe length too. I just have to crack my door open just a bit maybe a 1/16 inch to get it going good on a full reload for aout 10-15 min then it takes off. It is sensative about keeping the secondary burn going though

 

[LLigetfa]

Question? If the house is wanting to draw air in,why would the warm air still escape? Wouldn't those cracks be sucking in instead of letting out?

Following that train of thought, if the places where air normally leak in are sealed up then yes, places it would normally leak out could in theory reverse and air leak in. The house would have a pressure deficit which would affect the performance of the stove and may cause smoke puffing.

Regardless of whether you suck warm air out with the stove or you let warm air leak out through cracks, the amount of air leaking out has to be replaced by cold air leaking in somewhere. With the OAK the stove would perform better but still be prone to smoke puffing if the deficit is not addressed. The OAK could possibly push more smoke into the home.

 

[Troutchaser]

They should sell an engineer with these stoves.

 

[begreen]

That's standard on Italian stoves

 

[ChillyNoMore]

Thanks for all the encouraging responses! I think I now have a good set-up to get started with:
- stovepipe adapter with damper
- 68" telescoping double walled stovepipe
- ceiling support box
- 60" class A chimney pipe
- VacuStack cap (in the mail)
- roof brace (the forecast is calling for 50 mph winds tomorrow!)

This is a straight up and out installation so hopefully it won't be too tricky. Now all we need is one or two dry days in a row!

Any final tips on putting the DuraVent together? In particular, which parts should and which should not be sealed with high temp silicone? I have read some threads on the topic but am still a bit confused. The installer said he would use a few dabs between the pipe sections, but I thought that you want to be able to take everything apart for cleaning...

Thanks again for all the help!

 

[begreen]

No sealant is used on the venting pipe joints. Use a generous bead of rtv or a regular good quality silicone adhesive sealant on the exterior storm collar rim where it contacts the pipe.

FWIW, It seems like too little pipe. I suspect that the 68" pipe will not be fully extended. If it is say 60", then 60" + 60" is only 10 feet. Although the wind blows a lot in the gorge, there are calm days too. The stove may draft poorly on those days.

 

[LLigetfa]

No sealant is used on the venting pipe joints...

Normally true but in some cases with driving rain, a thin bead down the vertical seam of the class A pipe may be warranted. Small dabs at the gaps caused by the folded seam of the interior smoke pipe wouldn't hurt either. It may help to hammer the seam a little flatter too where two sections meet.

 

[begreen]

True, I had to do that on our old Selkirk pipe installation. On the two new Simpson pipe installations I haven't had to caulk the seam at all. 3 years later on the house system, not a drip. In November we had some biblical rains so I did expect this, but no problems.

 

[Nic36]

Ditto on the Selkirk. I had to do the same with mine.

 

[cruiser]

I have a scan 61 also,, new this year too,, Its in my basement of my rancher, and I'm in the Pa mountains near a big elevation change, so its also windy. I'm getting one of those caps for next year. I have issue getting the stove to burn on secondaries,, I think the chimney is a tad short.. from where it comes out the basement wall to the top is only about 12' or so.. Thinking about adding another 2' section to see if it makes a difference. I seam to have to run the stove almost wide open to get the temps right,, and them it really puts out some serious heat!!