When I built my chimney in my outdoor boiler's building, I researched what size most boilers and stoves were using for chimney flue size. I also asked several installers for advice. I compared firebox size and loading door sizes too.
I had always thought that an 8" chimney was the best. But I went with the smaller of my two choices, which is 6.5" x 6.5" inside dimension square flue red ceramic flue liner. The chimney is inside the heated boiler room, total flue height from boiler to top of chimney is about 12'.
The main reason I went with the smaller choice was that I was told by several installers and chimney sweeping guys that the smaller flue will stay cleaner longer because it will be warmer and accumulate less creosote than a large flue..
With my smaller boiler this chimney worked well, even when I opened the loading door to toss wood or coal on the fire. But with my new, much larger boiler I'm getting a lot of smoke out of the firebox when I open the door to load in more wood and coal. Both the old boiler and the new one have a hinged flap over the top 1/3 of the door opening to help block smoke exiting the doorway, it swings out of the way when loading fuel. However, the new boiler has a much larger door opening, and this is the main problem I'm sure. But I need the larger door opening for faster and easier loading.
I have a smoke diverter built into the firebox, so before I open the door, I slide the diverter open which gives a direct pathway from the firebox to the chimney.. I let it draw for a minute or two to get some velocity up the chimney. I can see a significant increase in velocity of the smoke exiting the chimney when I check outside. I also turn off the combustion blower if it is running.
So my question is this: Many if not most of the folks on this site have a 6" stainless steel flue liner in their chimney. If I install a SS liner I will be reducing the area of the chimney flue from 6.5x6.5" square to 6" round. But the liner will get hotter faster than the ceramic liner. With less area, but round and warmer faster will I get better draft??
So has anyone made a before and after comparison when installing a SS flue liner ?? Does the SS liner pull a stronger draft than the ceramic flue?? The ceramic flue is brand new, clean, and I made sure the joints lined up very well so it is quite smooth all the way.
This is really just a comfort or cosmetic issue for me since the boiler is in it's own building and the only issue is me having to deal with the smoke [burning eyes, and smelly clothes] when loading the firebox. The boiler has plenty of draft when the door is closed, in fact maybe too much draft at times.
Also is has been very warm here for the last week or so, maybe I'm just seeing the poor draft because of the warm outside temperature?? The smoke was still an issue a few weeks a go when it was cooler.
Thanks in advance for any and all replies. Greg L [LsFarm]