Adding a Class A Extension

[BCC_Burner]

My NC-30 is currently connected to 5 feet of stove pipe, with 2 45's into a tee, with ~11 feet of insulated liner running up an exterior masonry chimney with a top play and cap at the terminus of it.

Throughout last winter the stove performed well, better than I expected given the shortness of my chimney and the decent condition of my wood. I am planning on upgrading my system a bit for next year to try to gain some additional performance and a cleaner burn.

First, I am replacing my interior single wall stove pipe with all double wall in order to keep my flue gasses that much hotter. That is a straightforward, plug and play swap.

Second, I would like to extend the height of my chimney to strengthen my draft. It looks like the longest single piece of Class A you can buy is 4 feet, and in the interest of simplicity, I would like to go with a single piece extension, which means I'll be adding 4 feet to the chimney.

What do I need to make the connection from the liner/top plate to the Class A piece? I also assume that the extension will need to be braced in some way so that is is secure. I have seen telescoping braces which can be fixed to the roof, but I am concerned with snow shedding causing those to fail and taking down the chimney extension. I have also seen a "Roof Support Package" which looks like it is meant to affix Class A to a roof. Could this be used to affix the extension to the top of the masonry chimney?

Thanks for the advice.

 

[webby3650]

You can use an anchor plate that is made for the chimney you choose. You remove the top plate, and attach the liner the bottom of the anchor plate. Then the class a continues from there up.
It would be best to remove some of the crown, bolt the plate down to the masonry and pour new cement over the plate.
It's not technically what this part is for, but its a solution for your problem.

 

[bholler]

I agree with webby3650 about using the anchor place but i would not pour the crown over top of the anchor plate. If the crown is solid i would just attach the place down with expanding anchors and silicone if it isn't solid pour a new one first and then attach the anchor plate. The only reason i say this is the fact that if any part needs replaced in the future you would need to remove the crown to do so. Also many of the installs i have seen done this way end up cracking above the plate. Either way will work but i think putting the plate on top of the crown is better in my opinion.

 

[webby3650]

I agree with webby3650 about using the anchor place but i would not pour the crown over top of the anchor plate. If the crown is solid i would just attach the place down with expanding anchors and silicone if it isn't solid pour a new one first and then attach the anchor plate. The only reason i say this is the fact that if any part needs replaced in the future you would need to remove the crown to do so. Also many of the installs i have seen done this way end up cracking above the plate. Either way will work but i think putting the plate on top of the crown is better in my opinion.

I just fear that a 4' section will be way too top heavy and end up on the ground one day.

 

[bholler]

It should be fine as long as the masonry it is attached to is solid and you use good expanding anchors i would not trust tapcons for it.

 

[begreen]

I just fear that a 4' section will be way too top heavy and end up on the ground one day.

Agreed. That is a lot of leverage relying on the brick bonds. Maybe better to have a mason extend the chimney, then extend the liner?

 

[BCC_Burner]

Thanks for the ideas so far. Unfortunately extending the chimney is not an option. It is a rental property, and any chimney extension would have to be removable, as my landlord thinks it will ruin the aesthetic of the cabin. If I owned the place I would have closed off the masonry chimney and run the chimney in a more central location, but I digress.

Are there braces that use steel cable instead of telescoping legs? This is how my electric service is braced to the roof and that brace appears to be low profile enough to not encounter snow issues.

Alternatively, what is the longest extension you would feel comfortable putting atop an anchor plate? With a chimney system as short as mine, even adding 2 or 3 feet should make a difference in the draft, especially when combined with the switch from single to double wall inside.

 

[begreen]

In order to see how this will affect draft I would do a test with cheap, 6" round galvanized duct pipe. Get two, 2 ft lengths. On a calm day, pull the cap and insert the crimped end of the pipe into the liner. Try the stove and note if there is an improvement. Then add the second piece of pipe and compare the difference in burning.

 

[BCC_Burner]

In order to see how this will affect draft I would do a test with cheap, 6" round galvanized duct pipe. Get two, 2 ft lengths. On a calm day, pull the cap and insert the crimped end of the pipe into the liner. Try the stove and note if there is an improvement. Then add the second piece of pipe and compare the difference in burning.

I did that test last fall and noticed a difference with both the 2 foot and 4 foot extension. I didn't go ahead with a more permanent modification at the time due to snow and lack of knowledge for how to properly affix it. Now that I have a few months before winter again I would like to get it figured out.

 

[begreen]

Sounds good. All I can add is that if you choose to go with a 4ft extension, do it as securely as possible. Guy wires probably would help. Post a picture of the chimney and maybe some of the pros will have more ideas.

 

[BCC_Burner]

Thanks BeGreen, I will get some pictures posted up this evening or tomorrow. I would rather deal with the draft the way it is now, as it is perfectly adequate than risk snow or wind toppling part of the chimney in the night when the stove is loaded. Obviously if there is a way to securely extend it for a few hundred bucks that would be great.

 

[double-d]

I see that there are Single wall Stainless Flue extenders available. You can add 2 of them and get about 35" and they are easily removable. Here is how it is advertised by Rockford Chimney Supply- others may also offer these.
Need to offset 2 chimney liner caps adjacent from each other or extend your flue above the roof line? This little wonder provides an 18 inch offset / extension. Fits perfectly on to the top plate collar and accepts the Quick Connect Rain Caps at the top of the flue extender. A perfect fit every time for your stainless steel flue liner!

 

[BCC_Burner]

I see that there are Single wall Stainless Flue extenders available. You can add 2 of them and get about 35" and they are easily removable. Here is how it is advertised by Rockford Chimney Supply- others may also offer these.
Need to offset 2 chimney liner caps adjacent from each other or extend your flue above the roof line? This little wonder provides an 18 inch offset / extension. Fits perfectly on to the top plate collar and accepts the Quick Connect Rain Caps at the top of the flue extender. A perfect fit every time for your stainless steel flue liner!

I have seen those and was thinking about them but I am pretty sure they are insulated double wall pieces, looking at the price and description. Still run into the issue of how to secure it though.

 

[bholler]

i have used the anchor plate a few times and never had any issues that is what they are designed to do as long as the masonry is in good shape there will not be a problem. If the masonry isnt that great just use some guy wires you can buy stailess cable at most good hardware stores attache them to the chimney with a big ss hose clam and anchor them to the roof how ever you can and it wont be an issue.

 

[webby3650]

I really don't see how an adjustable roof brace kit would ever pose an issue either. We install them all the time and have never had any issues with them. I think it would look better and would no doubt be more secure.

 

[BCC_Burner]

I really don't see how an adjustable roof brace kit would ever pose an issue either. We install them all the time and have never had any issues with them. I think it would look better and would no doubt be more secure.

I agree the brace is the best option for the non-snowy months, but I am concerned about it's ability to withstand serious snow shedding for 7 months a year. It seems like I would have to also install a cricket above each brace leg.

I will post some pictures this evening or tomorrow, but my hesitation with the roof brace has to do with its positioning. It would have to be secured relatively low on the pitch of the roof. This would give shedding snow a lot of room to build up mass and momentum before it finally breaks free and washes over the edge. I am worried this force will break or damage the braces, thus pulling the extension down. If I could attach the braces up near the peak of the roof I wouldn't be as concerned.

 

[bholler]

So then use cables they will cut through the snow better being thinner but in border for cables to work you need to have 3 opposing cables so as long as the chimney isn't on the edge of the roof they will work fine. Other wise use roof supports all of the solutions that have been given here are used all the time and all work well. i see no problem with just using the anchor plate but if you feel you need extra support just pick one of the options and go for it if the snow hasn't taken the chimney down yet it shouldn't tear off the roof supports.

 

[webby3650]

The braces are only 1/2" pipe with a 2"x2" angle bracket that mount vertically on the roof with several screws. The legs will be several feet apart, I can't imagine it would hold back snow.

 

[BCC_Burner]

I guess the problem isn't so much that the braces will hold a slab on the roof, although they will, the flush mounted guy wires coming off my electrical service hold up a shocking amount of snow considering they are two cables less than 1/4 of an inch in diameter. Wish it was still winter so I could post a photo, but they hold up ALL of the snow that is above them in a cohesive slab long after the rest of the 14/12 pitched metal roof has shed.

The issue I am foreseeing is that when the roof sheds above the braces, it is going to be a large slab with a lot of weight and speed washing over the braces. My house sees between 350 and 400 inches of snow per winter, so it's a large amount of snow on a regular basis. I wish the braces could be designed with a shear bolt that would break and detach them from the chimney before it is pulled down.

 

[bholler]

Well the way i see it you are either going to have to trust that the anchor plate will hold or you need to support it with something attached to the roof which you don"t think will work. Those are the only 2 options i can think of post a pic of the setup and we might understand better

 

[BCC_Burner]

Well the way i see it you are either going to have to trust that the anchor plate will hold or you need to support it with something attached to the roof which you don"t think will work. Those are the only 2 options i can think of post a pic of the setup and we might understand better

Indeed. I am leaning toward the anchor plate as I don't get much wind usually. I will take some pictures and get them up tomorrow, my personal computer is out of commission, so I'm relegated to posting at work. I definitely appreciate the advice.

 

[BCC_Burner]

Now that burning season is getting close, I am planning to go ahead and add a 4 foot section of class A to my stack. After a lot of deliberation, I think the best way to secure it will be with a roof brace kit, so I am going to go that route. I'm also adding a Vacu-stack chimney cap to the top of the addition, so between those two things and having significantly drier wood, the stove should be running a lot better this winter.

 

[begreen]

Sounds like a plan. At your altitude the additional flue is going to help. Couple that with the double-wall stove pipe and good dry wood and you should see a nice improvement this season.