Fire Slowly Dies?

Cap wrote:I have the same problem using a Harman Mark III. I cannot keep a coal fire going for 12 hrs unattended, maybe not 8 hrs. This will be my 4th season burning coal. When it dies, I have at quite a bit of unburnt coal left behind. I believe my problem lies within my flue. The Mark III has a 6" outlet. My flue is 8" x 34' high. My thinking is as the outside temps drop overnight, and the stove cools off a bit, my draft slows down allowing the fire to die. I typically would add a wood log on top of the fire at night in order to maintain a fire till morning. Does anyone believe my theory is correct? I am debating adding a 6" ss liner but at $550, I want to be sure this is the answer.

Comments appreciated,
Cap
Lehigh Twp, PA

You're venting a 6" stove into an 8" flue and the area ratio is about 2.2....that is, your 8" flue is 2.2 times the area of your 6" stove exit area and this kills your draft for two reasons: 1) when rising gases "see" this expanded 8" flue area, they expand and slow down and 2) they cool off, both of which reduces draft.

Installing a 6" liner all the way to the chimney top takes care of the area ratio problem but if you have an exterior chimney where say, 3 of the 4 sides are exposed to the outside, then the liner will be sitting in a "cold" flue tile area and draft may also be negatively affected. When I installed my wood stove liner, I put 1/2" insulation on the liner and then shoved it into the flue. This takes care of the area ratio problem and keeps the liner warm, both of which improve draft.

Hello Castiron--

Welcome to the forum. Thanks for the insight. I tangled with this problem two winters ago. Check the dates on the messages.

I did install the ss liner and I do agree with all of your points.

But I had no room to insulate the liner as it was a snug fit. The insulation would of peeled off as I shoved the liner downward. If I get the energy, time and desire, I may use perlite to insulate the void between the liner and the clay tile.

My current stove really drafts good now without insulation. And I do have 3 exterior sides to my flue. The perlite idea may be more trouble then it is worth. Difficult too.

I burn with a VC vigilant and have similar situations when the coal burns too fast. If it is a slow burn then I have more control but if fast then the ash buildup is excessive and shaking must be done very frequently. When my stove is burning good then (do this with no lights) the firebox is blue with the burning coal/coal gas. If always orange then it is probably burning too fast.

Cap wrote:Hello Castiron--

Welcome to the forum. Thanks for the insight. I tangled with this problem two winters ago. Check the dates on the messages.

I did install the ss liner and I do agree with all of your points.

But I had no room to insulate the liner as it was a snug fit. The insulation would of peeled off as I shoved the liner downward. If I get the energy, time and desire, I may use perlite to insulate the void between the liner and the clay tile.

My current stove really drafts good now without insulation. And I do have 3 exterior sides to my flue. The perlite idea may be more trouble then it is worth. Difficult too.

I agree about the pearlite being a problem...you then permanently narrow your flue and deny yourself the ability to put in larger liners in the future and, there are other problems. You did the right thing installing what you could get down the existing flue. Even with no insulation, a ss liner should take a wood chimney fire and your clay liner is then a back-up. Also, if you use coal, there's no cresote and you'll have lower stack temps so a fire should be remote.....