OVERDRAFT?

[jqgs214]

Been reading some of thse post on overdraft issues. I think I may have a slight overdraft because of slightly lower than expected burn times compared to what I'm reading and when I damper down all the way I still get white flame when I have a hot fire going. Is this normal, I have an insert and was wondering if a damper is possible (worth it?) on one with a S.S. flex liner? The chineny is approx 19 ft

 

[MountainStoveGuy]

when you turn the stove all the way down, does it still burn fast and hot? How long are you getting on burn times? what kind of wood are you burning? is the wood cut for the proper size to fill up the firebox?
19 is tall, but its not that tall. If it were a free standing stove that i sold you, i would have put a damper in it. In my neck of the woods, i dont start adding dampers until about 20', but altitude plays a big part in draft, or the lack of draft At sealevel, i would start adding dampers at about 16'.

 

[jqgs214]

I would not say fast and hot but not as slow as I would think it should, the secondaries seem to crank fast jets out of the tubes when I have a good hot fire thats dampered all the way. That 19' is an estimate never actually measured, but since I have 2 stories (2nd is nut full height, really a finished attic) I think its around that. If I needed to damper my insert how would one go about doing that? The longest I can sustain any type of flame is 3+hours and thats with a fully loaded box and maybe dampered down a little before it should. I get 4+ hours and still have real good coal bed for refills.

 

[MountainStoveGuy]

with a 1.3 cf firebox, i would say your right on target. Doenst sound like you have a problem to me.
I have no idea about dampers and inserts.. i would be courious how that would work, mabey another member can help us out.

 

[Jay H]

I'm kind of wondering the same thing about my stove... I can damper down the entire air vents and don't exactly notice a dieing of the fire, in fact, it might just be me, but I can maintain the 400deg flue temp (using a probe thermometer) with all the vents closed.

I have a 2.0cf Quad 3100, vented to a 6" double wall Selkirk flue which I am guessing to be in the range of 15'. I live at about 830' ASL...

Any idea whether I should look into a damper or not. I'm going to measure my second floor (not a full second floor) and guestimate the flue length above my roofline tonight or so..

Jay

 

[MountainStoveGuy]

Jay, you should be getting 4-6 hours out of your 3100. Your chimney hight is perfect. In a overdraft situation, the fire is unresponsive from open to closed. When you shut down the primary, the secondary is forced through the system by draft. If you have to much secondary, then nothing burns and goes right up the chimmey. If your getting good secondary combustion, and the burn time listed above, then you are in the sweet spot of your stove.

 

[jqgs214]

So, if in overdraft the secondary cant do its job the stack will smoke?? If thats the case then I have no problems because I get very little smoke when I have a good fire going dampered down. Thanks

 

[MountainStoveGuy]

yes, but sometimes the fireplace is so darn hot the smoke burns anyway. WxMan, i think your good to go. What i was trying to say, is that when your stove overdrafts, it pulls smoke and heat out faster then the stove can burn, increasing stove pipe temps and decreasing stove top temps. It doenst necessarly mean you have a smokey stack, when the flue gas gets to 1200* nothing is going to survive.

 

[elkimmeg]

MSg a reminder not all of us start a mile high and the rule of thumbs, though valid for your elevation, might not be at a few hunderd feet at sea level

we can get away with more verticle height without the need to install an inline damper./

 

[MountainStoveGuy]

whats the minimum chimney that you would put a damper on? here is 20' , i was guessing 16 at sea level.

 

[jqgs214]

MSG, thats revese of pressure principle. More pressure at sea level so less chance of overdraft with longer chimney. Elk would be the expert for how high but as far as air pressures to overcome, its easier the higher you go.

 

[Andre B.]

MSG, thats revese of pressure principle. More pressure at sea level so less chance of overdraft with longer chimney. Elk would be the expert for how high but as far as air pressures to overcome, its easier the higher you go.

Every book I have says that at higher altitudes you need a taller chimney to get the same draft for the same temperature difference.

 

[MountainStoveGuy]

yes, i made a mistake. LOL. thats absoluty correct, so when do you add a damper at sea level?

 

[Scraper]

Great thread considering my issues are the same. Discounting altitude, I have a Quadrafire 5100i (insert) which has been having these issues as well. I also run a Quadra-Fire 4300 Step-Top freestanding in the basement. I tried curing these overdraft issues by removing the damper plate and grinding down the "stops" making it so it completely covers the damper hole. This has not worked casuing problems with out of control burns. The 4300 in the basement allows full control of the fire after complete dampering down. When the wood is properly ignited and burned when fully dampered you only get secondary combustion flames as opposed to burning wood flames. I cannot get that with the 5100. After complete dampering, the fire continues to go and you can hear the air being sucked in. I was just told by my dealertoday to try an "air dam" on top of the bricks. What he said was to cut a brick in half and use both pieces on top of the brick top casing. Put them in a "V" position near the exhaust port. He said this would slow down air flow up the flue even more. I also use a SS liner and have about a 20' shot to the top. I will not be trying this until after this burn season, but was wondering if anyone else has used this scenario to correct overdraft issues?