What should the proper level of draft be?

[Bluerubi]

I just swapped the stock cap from the 6" steel chimney liner on my insert to a giant cage that covers the entire top of my chimney. Even in warm conditions yesterday the draft is dramatically stronger than it has ever been before, to the point where I can't slow the burn down to the level I was able to do prior to the change. I've always had the more restrictive cap ( had a bunch of small slots in it for smoke to exit), so all I know for sure right now is that my VC Merrimack is behaving differently. Don't know if it's bad or not, just different and far more aggressive.

Door gaskets were all replaced mid last year after miserably failing the dollar bill test, and appear to all still be good now. I also just replaced the loose gasket between the glass and the door, so I feel like the stove is tighter than ever. Prior to the new cap I would always get some black buildup on the glass at the most restrictive setting, but woke up this morning to crystal clear glass which is a first. Liner is about 30' long on an outside chimney, and the first indication something was up was when I was able to close the door immediately after lighting the fire last night with no smoke accumulation in the box, something that never happened in the past.

Any thoughts on what the fire "should" look like on an insert when running properly? With only a few splits in I was able to get some flames from my secondaries last night, but there were also steady flames coming off the wood the whole time. There is a very clear difference between wide open air and shut down, it just feels like I can't go as low as before, and I'm concerned about how intensely this will burn once the temps get lower outside. I'm fine with digging into this further to fix any issue there might be, but as the sole wood burner in my social network it's tough to determine if what I'm seeing is correct with limited reference points.

Thanks for the help.

 

[begreen]

Given all the changes the fire is bound to burn quite differently. It could be the different flame pattern is due to the air wash working better. To eliminate variables maybe run with the old cap for a little while and see if the flame changes or stays they same?

 

[Bluerubi]

Given all the changes the fire is bound to burn quite differently. It could be the different flame pattern is due to the air wash working better. To eliminate variables maybe run with the old cap for a little while and see if the flame changes or stays they same?

I expected an improvement during the historically low draft conditions, but honestly never considered managing the potential increase on the other end. I like the idea of swapping the cap just to be sure nothing else has changed, but I disposed of it when the new one was installed, so unfortunately not an option. I get a serious case of wobbly knees as I approach the cap on the ladder since the 40ft extension doesn't make it high enough, and have to get my neighbors 60ft, so I hired out the job of cleaning and cap swap this year.

Any tricks out there other than the dollar bill test to check on gaskets? I used to have access to pressure sensitive paper that I was thinking would work well if I could secure it somehow, but didn't want to go into a big root cause analysis if there really isn't a problem to be solved.

I guess what I'm really wondering is if the fire was hot, but manageable on the lowest air setting, and 60F/rainy outdoors, is it going to be a huge difference at 0F and windy? I just remember struggling in the past on warmer days to get a decent draft started, and no issues in the middle of winter, so I'm picturing a blast furnace once the temperature drop further with my current setup.

 

[begreen]

The dollar bill test all the way around the door should be adequate. You might also check the air control valve to make sure it is working correctly. On some stoves there is a pivot screw that if loose can cause sloppy air control.

 

[mellow]

30 feet is quite a bit of liner, are you able to install a damper?

 

[Woody Stover]

Not sure if he will be able to put a key damper on the insert, or if there are other ways to do that. If he had the old cap, he could have maybe altered it to split the difference between the weak and strong draft.....

 

[mellow]

Ahh yes, saw the freestanding on his avatar and that threw me off. There have been past conversations about how to slow the draft on an insert with a tall liner, some were successful with blocking the secondary air intakes so not as much air was sucked in. I have seen others put a key damper IN the liner to help slow down the draft as well, I would link to it but AS is down at the moment.

 

[begreen]

I can see putting a key damper in a rigid liner but not in a thin foil one. One possibility is to investigate the intake air valve and see if the stop could be adjusted to allow it to close a bit more, but not all the way closed.

 

[Bluerubi]

I checked out the gate that the air control operates, and it appears to fully close over the holes that feed my air wash. Beyond that I don't think it impacts the air that is injected into the coals from down below, or my secondary tubes, so not much more I can do there I think. I think I'm going to open up the bottom of the insert to see if I can find the holes where all the air is drawn in to see if I can partially block them off. This is of course assuming I actually have a problem, since I still don't know if the level of fire is really that bad.

What should the realistic expectation be for how far you can turn down the fire? In the past I could essentially shut it down to where I had no visible flames except around the burn tubes (always had dirty glass), but now I get fairly lazy flames off the wood and some secondary action (glass is pristine). If this is the way it would run all winter I would probably be okay with it, but I'm uncertain how much more aggressive things will get once the draft gets stronger in colder weather. I hope I'm just being paranoid, but the engineer in me sees a distinct difference in my process, and I don't have a point of reference to drive my actions towards letting it ride or digging in and looking for air leaks.

I should probably change my image as well. Has nothing to do with current stoves or my login, so I can easily see the confusion.