Is there a down side (other than cost) to adding additional chimney height?

[Slow1]

Other than the cost, if you are running an external SS chimney is there a downside to adding an additional 2-3 feet of chimney on the top?

My situation is that my draft seems a bit weak - on cold start I have to use a hair drier to get started etc. Today after a few hours of burning I started to have some backpuffing. I hate to admit it but I have had a couple other instances of this before. Seems to happen when things are cooling down. Stove top was plenty warm - 350 range, flue was below 200 surface temp though. There was one piece of wood still looking like wood in the firebox along with coals. Air set to about 3/4. Outside it was about 40-45* and no wind at all, inside close to 70. Puffs were mild, but enough to push smoke into room that I could smell and see. I had been outside and when I walked in it was obvious that something was up. I opened a window and didn't notice an immediate change, but I have no idea how quickly this 'cure' is supposed to help if it is indeed a 'negative pressure' issue. Given the amount of traffic in and out of the house this morning (thus doors opened/closed) I find it hard to imagine house had built up a negative pressure, but who knows...

By the numbers I think I'm right on the marginal line for chimney. Looking at the pieces and estimating based on counting 3' and 2' sections out there I think I have 14' outside and just over 2' above the flue collar (making 16' total) but then there are the two 90* bends inside and a couple 30* (?) bends near the top on the outside to get around the edge of the roof as well as the short horizontal run to get through the wall to the "T". I'm sure someone can add all those twists and turns in and figure out what impact that has on draft.... Spec calls for 14' above flue collar. So, I'm considering adding a section to the top but want to be sure that there isn't an argument against it. I'm wondering if it may cause the flue gases to cool too much and collect or anything like that.

Thoughts anyone?

 

[begreen]

No real downside and it could make a nice improvement. Well, there will be a bit more pipe to clean, but that's about it.

 

[Slow1]

Do flue gases cool a lot more as they travel up an extra 2-3 feet? Also, taking into consideration that this is giong to be sticking up quite a bit above the roof, how much more would be the right amount to add? I don't want to have to go back and do this again - I also expect any cleaning *I* do will be bottom up and I'll have to hire someone to do any top-down cleanings unless I dismantle the pipe to do it after this... can't exactly put a ladder on top of the roof myself.

 

[firefighterjake]

Well I don't have any concrete numbers for you Slow . . . but try adding another 3-4 foot length and see if this doesn't improve things for the draft.

As for the negatives . . . cost, perhaps need to secure the longer length depending on how much taller it makes the flue . . . cleaning another 3 feet or so shouldn't be an issue . . . you may need to buy another rod perhaps, but the extra 3 feet shouldn't lead to a huge amount of creosote build-up . . . I'm running 20 feet or so of outside Class A pipe and I haven't had any issues . . . I get a bit of creosote near the cap and a little in the first foot or two where the T connects to the Class A, but nothing to write home about (last cleaning was maybe 3/4-1 cup of fine black creosote.

Oh yeah, definitely do the bottom up cleaning . . . works slick . . . fast, cheap and easy, assuming you have a T connection and that the 30 degree bends aren't too troublesome.

 

[LLigetfa]

Depending on how well the stove can be controlled, too much additional draft could create issues. The RSF I had in my former home had too a large notch in the butterfly and so could not choke off the air enough. When I stoked it for overnight, it had a propensity to run away.

The way the excess draft worked, the hotter the fire, the more draft. The more draft, the hotter the fire. Reminded me of an old car I had where the seat adjust was broken. When you stepped on the brake, the seat would slide forward, applying more brake. More brake meant the seat slid more.

 

[Backwoods Savage]

Slow, why not head to the hardware and get a 3' length of regular stove pipe? Stick that on top and see if it makes any difference. If it does, then an insulated 3' or 4' piece will be the answer.

 

[dondude]

Backwoods great idea instead of wasting $100 bucks.

 

[Slow1]

Slow, why not head to the hardware and get a 3' length of regular stove pipe? Stick that on top and see if it makes any difference. If it does, then an insulated 3' or 4' piece will be the answer.

If I do the job I'm going to have to have someone else install it - for a variety of reasons I just can't get up there myself. So, if I have to pay someone to come over and stick something up there I may as well pay the labor once and be done with it rather than twice.

I actually broke down and called the good folks at woodstock today to discuss the situation. The advice there was basically to run with more air and see how things go once it gets colder. Since my problem is not constant and I did have it choked back to a rather low burn rate/temp it was his opinion that simply running a bit more air through would mitigate any issues during these cool but not cold days.

Second line of defense if it happens again will be to go with the open window test - i.e. don't mess with the stove and give the open window a good 10 minutes to resolve the issue (I only gave it a couple minutes this morning - I just didn't have the patience to see those puffs). If that resolves it then it will pull me toward a different direction for resolving things... if the window doesn't fix it then back to the chimney perhaps (?).

In any case though, I still envy folks who have enough natural draft that they can do cold starts without having to warm their chimney. So I wonder if adding a few feet of pipe could help with that (puffing aside). Although I'm not sure if a few more feet of COLD pipe really will help or just make for more to heat up with the hair drier.

 

[[email protected]]

Slow, I know you were the one with the question, but I'm new here. How do you measure the flu temp, and do yo know what the flu temp should be?

Oh yeah. IMVHOP - I like Backwoods suggestion. But is sounds like your concerned about getting up on to the roof more than once. Don't forget that when/ if you add the extra footage to your flu top, you'll probably need to add a roof brace. I know with Selkirk, anything over 5' above the roof surface needs a brace.

 

[Slow1]

Slow, I know you were the one with the question, but I'm new here. How do you measure the flu temp, and do yo know what the flu temp should be?

I measure it using a magnetic thermometer attached to my single wall pipe about 20" above the flue collar. As to the right temperature - I don't know if there is a "right" one. Woodstock folks say they expect it to go down once the cat is engaged. Seems that around here folks report surface temps on the pipe of 250* +/-50* to be fairly normal operating range for the fireview.

Oh yeah. IMVHOP - I like Backwoods suggestion. But is sounds like your concerned about getting up on to the roof more than once. Don't forget that when/ if you add the extra footage to your flu top, you'll probably need to add a roof brace. I know with Selkirk, anything over 5' above the roof surface needs a brace.

I have a brace already in place - I don't know if I'll need to adjust it or add additional. The sweep that installed my pipe (and who I've already asked to quote additional length) will likely tell me what additional bracing will be needed. I tend to trust his judgement on this matter - so far the install seems to have been quite solid (has been up for a year and hasn't fallen down yet - guess that counts for something? ha!).

 

[CTburning]

There are other issues that effect draft. Wind can cause draft issues and puffing. I live in a river valley with a "mountain" as a backyard and large Oaks all around. My setup is a triple wall pipe that goes up the side of the house. Unfortunately it faces the side the wind comes from. I spoke with Woodstock last year because I was having minor draft issues with my old Garrison wood stove and I was worried that the cooler flue temps of the Fireview would magnify my problem. I also visited one of the local stove dealers and spoke with an installer who was very helpful. I purchased a wind inducing chimney cap online and it seemed to help. My other options include adding another 3 ft or building a chase around the pipe. Both would help with draft. I have had a Fireview sitting in my garage for almost 8 months now and I'm dying to hook it up. I am interested to hear of your solution and wish you Good Luck!

 

[learnin to burn]

Slow1 - General rule of thumb is for every 90 degree elbow subtract 5 feet from the height. So in your case with 16 feet and 2 90's your at 6 feet effective chimney height. Add to that 2 30 degree turns (I'm guessing here) to be safe subtract 3 more feet which would give you about 3 feet.

Check your specs again and see if the 14 foot minimum is for strait up or for a thought the wall application?

I agree with you trying to run it a little hotter before making a lot of changes and adding expense. If this works there would be no need for change unless it's a drastic reduction in burn time.

You can also try using double wall stove pipe inside which will help keep your flue temps higher.

 

[PunKid8888]

Slow, why not head to the hardware and get a 3' length of regular stove pipe? Stick that on top and see if it makes any difference. If it does, then an insulated 3' or 4' piece will be the answer.

My cousin did this exact same experiment. Only thing is it worked extemly well and he has not replaced the stove pipe section with real class A because he will need a roof support. I bug him about it every time I am over there.

 

[Slow1]

update: I went ahead and added 3' today. Of course I had a great draft after the addition - being that it was 17f outside at the time and the stove actually was still warm (had to idle it before the sweep arrived to do the install but there were still coals). Jury will have to deliberate for a while before I will know how much of a difference it will make I imagine - need some warmer days to get those marginal temps. However, one thing I did notice just looking at it is that it is now clearly taller than the ridge of my house so IF there was ever any sort of wind direction issue with wind heading over the top of the house this should have fixed that at the same time! Easier to walk out the front door and check for smoke too, heh.

Went ahead and had the sweep pull the screen out of the cap while he was up there - he asked/suggested it. It had a little bit of build-up on it (had not been looked at since install - did bottom-up cleaning last time). Not enough build-up to impede flow I'm sure, but I imagine if I ever put some smoke up there it would build on the base faster than if the screen is gone eh? He looked down the pipe and said it looked fine - I wasn't in the mood to climb up there and look myself (whole reason I paid him to go up there and twist a section of pipe on in the first place eh?)

As mentioned before, draft seemed good and strong afterwards. Got the stove lit and up to temp right quick when all was done - but never had a problem doing this and haven't been having any complaints during cold weather in any case.

Will try and remember to post an update once I get some run time with the additional pipe in place in case anyone is interested.

 

[fire_man]

I'll bet the additional height fixed your problem, you have a lot of bends in your setup that need the extra height. These cold temps definitely can mask a draft problem so it might be a while around Eastern MA before we get high enough temps to verify your fixed worked. Keep us posted! :cheese:

 

[woodracerx]

update: I went ahead and added 3' today. Of course I had a great draft after the addition - being that it was 17f outside at the time and the stove actually was still warm (had to idle it before the sweep arrived to do the install but there were still coals). Jury will have to deliberate for a while before I will know how much of a difference it will make I imagine - need some warmer days to get those marginal temps. However, one thing I did notice just looking at it is that it is now clearly taller than the ridge of my house so IF there was ever any sort of wind direction issue with wind heading over the top of the house this should have fixed that at the same time! Easier to walk out the front door and check for smoke too, heh.

Went ahead and had the sweep pull the screen out of the cap while he was up there - he asked/suggested it. It had a little bit of build-up on it (had not been looked at since install - did bottom-up cleaning last time). Not enough build-up to impede flow I'm sure, but I imagine if I ever put some smoke up there it would build on the base faster than if the screen is gone eh? He looked down the pipe and said it looked fine - I wasn't in the mood to climb up there and look myself (whole reason I paid him to go up there and twist a section of pipe on in the first place eh?)

As mentioned before, draft seemed good and strong afterwards. Got the stove lit and up to temp right quick when all was done - but never had a problem doing this and haven't been having any complaints during cold weather in any case.

Will try and remember to post an update once I get some run time with the additional pipe in place in case anyone is interested.

Of course we are interested we are wood burners

 

[oldjammer]

I'm interested !!

 

[Todd]

I think a lot of draft problems are created by chimney caps. I saw a chart once that showed how much these caps restrict the flow and it was substantial. There are some people that take them off during the burning season and put them back on in the summer to keep the critters out. Caps are also notorious for clogging.