Harman 2.6 burn troubles

[bruce]

I just upgraded from a Harman tl 200 to the newer 2.6 model
I have had a few test fires now and I cannot get this unit to burn hot enough, I run it up to 500-600 degrees and close the internal damper and it falls flat on its face down to around 200-250 with full air
my tl200 burned to hot and was tuff to keep dampered down
I have a masonry chimney 8x8 flue 20 ft above the thimble, is it possible this unit needs more chimney or an outside air kit?

 

[branchburner]

I wonder, were you getting a good secondary burn with the old tl200, or could it have been burning hot because the damper wasn't closing all the way, due to warping or another problem? All things equal, it doesn't really make sense that the old stove ran so hot and the new stove can't get the AB to light off, since the combustion package in both is a similar if not identical design.

My experience with the Oakwood is that stove top temps are not always a good indicator of whether there is a deep enough coal bed for the AB to engage and keep burning smoke. Especially from a cold stove, the temps can appear very high (700+) but I may still have insufficient coals to maintain secondary burn. So yes, then the stove temps quickly drop when I shut the bypass damper.

With a good coal bed on a reload, I would never need to open the air more than half way. But from a cold start, it takes quite a while to get the coal bed... how long are you waiting after starting the fire to shut the bypass?

In addition to not having a coal bed that is deep/hot enough, the 8x8 flue may be too large for optimal draft, as you have over 2x the cross-sectional area of a (28 sq in) 6" round flue that is the recommended size. The ability of a larger flue to draft sufficiently of course varies with each stove and house, but downdraft stoves like Harman are notoriously draft-sensitive in getting sustained secondary burns with the AB.

The other factor is wood quality -- what are you burning, and how long cut/split/stacked?

 

[bruce]

I wonder, were you getting a good secondary burn with the old tl200, or could it have been burning hot because the damper wasn't closing all the way, due to warping or another problem? All things equal, it doesn't really make sense that the old stove ran so hot and the new stove can't get the AB to light off, since the combustion package in both is a similar if not identical design.

My experience with the Oakwood is that stove top temps are not always a good indicator of whether there is a deep enough coal bed for the AB to engage and keep burning smoke. Especially from a cold stove, the temps can appear very high (700+) but I may still have insufficient coals to maintain secondary burn. So yes, then the stove temps quickly drop when I shut the bypass damper.

With a good coal bed on a reload, I would never need to open the air more than half way. But from a cold start, it takes quite a while to get the coal bed... how long are you waiting after starting the fire to shut the bypass?

In addition to not having a coal bed that is deep/hot enough, the 8x8 flue may be too large for optimal draft, as you have over 2x the cross-sectional area of a (28 sq in) 6" round flue that is the recommended size. The ability of a larger flue to draft sufficiently of course varies with each stove and house, but downdraft stoves like Harman are notoriously draft-sensitive in getting sustained secondary burns with the AB.

The other factor is wood quality -- what are you burning, and how long cut/split/stacked?

my wood is seasoned a year and is a mix of oak and cherry
I am trying other wood tonight to see if its a differance
is the oak a worth wild investment?

 

[branchburner]

My stove had a hard time with one-year oak, especially larger splits, unless the fire had already been going several hours.

From a cold start, I found using kindling, branch wood and smaller splits of VERY dry wood got me the ability to close the bypass more quickly. Otherwise, it was a longer wait, as the larger splits took quite a while to start coaling.