Minimum chimney height

[Tom Cat]

I've been thinking about having an insert installed into a masonary fireplace on an exterior wall. Most manufacturers recommend a minimum chimney height of 15 feet. Mine is probably closer to 12 feet from the hearth floor (I'm going to try and measure soon). Some retaliers/installers say that is OK, others are recommending a 3 foot chimney on top of the masonary. Overnight temps can easily fall below 0 F so I'm thinking the extension is probably needed to draft properly. Any insight is appreciated.

tom

 

[BrotherBart]

I would go with 15 feet. That is the height the stoves are designed for to perform well in the EPA testing. Well actually, 15 ft. +/- one foot.

 

[jeff_t]

It's not difficult to extend if needed, but it's probably easiest to do when the liner is installed. I say just do it and save a step down the road. What inserts are you considering? Some are more sensitive to draft than others.

As a general rule, colder temps result in a stronger draft, due to temperature differential. Sometimes super cold, dense air can have the opposite effect with the right atmospheric conditions, but I don't think it happens very often.

 

[Tom Cat]

I'm considering a PE super and a quardafire 2700 (may go to a 3100). These are carried by local dealers who will handle the installation. I've been having a difficult time figuring this out as there is a lot more involved than I originally thought. Like everyone I want to keep the cost down but more important is that I want it safe and reliable.

tom

 

[ddahlgren]

right or wrong I look at it as a two edged sword. Long enough to get a good draft but not so long the flue gases can cool and form creosote at the top. i would think height would be most draft sensitive in spring and fall and most creosote sensitive when the temps are around 0 and the top of the chimney very cold. My take on it and only mine. An interesting test would be a probe at the very top to see what the final temp really is.

 

[PapaDave]

there is a lot more involved than I originally thought.

You aren't alone. Many have come here with the idea of getting a stove/insert installed, only to find that there's more to it than they had thought.
Of prime concern should be the firewood. Do you have any yet?
If not, get crackin' on that right now, or you'll not be happy next winter, and you'll be back here wondering why the stove isn't working correctly.
It's the wood.
Don't know where you are, but if you have access to Ash, get that first....then get some more.......then get some more. Unless, of course, your first load is 10 full cord.
There are tons of extremely knowledgeable people on this site that are willing to help.
Insist on a block-off of some kind above the insert. Some will also suggest getting an insulated liner.
Keep us posted, and, we likey pics.
Just in case no one else has said it, welcome to the Hearth.

 

[Backwoods Savage]

Welcome to the forum Tom. It is not all cut and dried on the needed height but is on the recommended height. Usually one is better off with the recommended height or more. In addition, if there are bends in the flue or chimney then you need more height.

Still, depending upon your location and the lay of the land, some can get by with less than recommended but I still would not recommend going shorter for any new wood burner. You want the height so you get a good draw.

 

[Backwoods Savage]

right or wrong I look at it as a two edged sword. Long enough to get a good draft but not so long the flue gases can cool and form creosote at the top. i would think height would be most draft sensitive in spring and fall and most creosote sensitive when the temps are around 0 and the top of the chimney very cold. My take on it and only mine. An interesting test would be a probe at the very top to see what the final temp really is.

I am not sure I agree with your assessment. Especially the part about more creosote sensitive when temps are around 0. The reason for that is you will have a good fire going when it is zero and that should keep the chimney warm enough. For sure chimneys are more draft sensitive in spring and fall simply because there is not as much difference in the temperatures then. This is why some folks have big problems burning in fall or spring; especially when their fuel is marginal. Never forget: poor fuel = poor results.

 

[Sirburnsalot]

I am not sure I agree with your assessment. Especially the part about more creosote sensitive when temps are around 0. The reason for that is you will have a good fire going when it is zero and that should keep the chimney warm enough. For sure chimneys are more draft sensitive in spring and fall simply because there is not as much difference in the temperatures then. This is why some folks have big problems burning in fall or spring; especially when their fuel is marginal. Never forget: poor fuel = poor results.

Dry firewood is key. If you want good wood have it split, stacked, and covered by May at the latest. Cover the top of the pile only, not the sides so the pile can breathe. This is absolutely critical. Too many people get their wood too late in the season and what's worse, they have no idea if it's dry or not. Firewood suppliers like to tell you that their wood has been "seasoned" for an entire year. To this day, I still don't know what they mean by seasoned but one things for sure, it almost never means that the wood is dry. Lots of people have soaking wet firewood and don't even know so they blame the bad results on something else.

 

[rideau]

You said your chimney is 12 feet from the hearth. If you have a top venting insert, then you are likely only about 10 feet from the stove so you likely are talking a ten foot chimney for the stove. That's just too short. You need an extension.

 

[Tom Cat]

I measured this weekend and it's only 11 feet from the hearth. Chimney is 3 feet above the roof and close to 2 feet above anything within 10 feet. I say close since I didn't have a level. I will be doing most of my burning in the winter. It's a ski house so it gets little use fall and spring.

I plan on buying wood soon. I also have a lot of dead stuff on the property.

Tom

 

[rideau]

Try for minimum 15 feet actual chimney length. Life will be easier.

 

[Tom Cat]

No stove yet, but I did order wood. I figure if I end up waiting for a deal on the insert at least the wood will be well seasoned. All the advice is appreciated.

Tom

 

[dafattkidd]

So what's the proper way to extend this chimney. I need to do the same thing. I'm thinking I need at least another 24".

 

[Tom Cat]

I'm not sure. One member pointed out a chimney extender from Rockford, but it was 18 inches. One dealer I talked to wanted to put 3 feet of insulated chimney pipe - nice but fairly expensive. Another was just going to put 3 feet of stove pipe. So the top 3 feet would not be insulated.

My thinking was to use a 7 inch chimney cap and 7 inch stove pipe. Then the insulated liner could be extended to the top of the extension.

Tom

 

[begreen]

Do it right, add the 3 ft. The correct method depends on the existing installation. Sometimes the masonry chimney can be added on to, sometimes attaching a class A pipe extension is better. Pictures are very helpful here so that we can see what you see.

 

[OKchiefsfan]

I just installed a new ss liner for my Lopi Revere which called for a 15 ft minimum chimney height. I only had 11 ft so I purchased the double wall ss smooth liner and also insulated it and have not had any troubles with draft. I bought my liner from Rockford just in case I needed that extended flue piece. So far so good.

 

[Trilifter7]

I started with 12' of flue and noticed weak draft all the time but worst on start up or mild temps. I added a 3' section of triple wall duravent plus and it breaths much better now! I never get smoke in the room now even during mild temps. My pipe was about a foot over the roof line 15' away but now is way up there. It's almost 4' higher and I think it looks and drafts much better now. If you are on the fence about it you could always try sticking some cheap single wall pipe up there temporarily to see if it changes anything. If it does then go for it and your results will only be better when you put the correct insulated chimney piece on.

 

[etiger2007]

Could you guys post some pics of your chimney after you put your extension on? I may need to do one this summer also. Thanks.

 

[DAKSY]

So what's the proper way to extend this chimney. I need to do the same thing. I'm thinking I need at least another 24".

The least expensive way is to mount an anchor plate to the top of your chimney. It attaches to the top of the liner & the bottom of the Class A chimney pipe & is fastened directly to the masonry mudcap (crown). They are brand specific on the top side, tho, so you have to use one made by your Class A chimney manufacturer.
This is what ICC Excel's version looks like...

(broken link removed to http://www.icc-rsf.com/main.php?t=chem_produits&i=7&l=en)

 

[Backwoods Savage]

No stove yet, but I did order wood. I figure if I end up waiting for a deal on the insert at least the wood will be well seasoned. All the advice is appreciated.

Tom

Tom, I do hope you've ordered enough wood for all of next winter! If not, you definitely should.

 

[Tom Cat]

All the wood for next winter is on order and should be arriving soon. Waiting for the snow to melt. When I get the stove I'm planning to buy for the following year.

tom

 

[Backwoods Savage]

Sounds great Tom!