question on burn temps & cycles

[Sparky31]

As a new stove user one of the key tips I've picked up here at hearth.com is to burn hot, in order to minimize vapor condensation within the flue pipe and resulting creosote buildup. Jotul says to run my F400 between 400 and 600 deg external surface temp. I've done so, verifying with an IR thermometer.

But I read on woodheat.org that I should get that hot fire going, then turn down the air and allow the load to burn down to coals. The coals don't stay hot. They say to burn in cycles of heat, not to maintain a hot fire all the time.

I notice that the F400 secondaries really don't kick in at surface temps below about 550.

1) So how do I utilize the secondaries if I'm not burning hot at all times?

2) Does letting the wood load burn down to coals produce undue creosote?

My F400 has been running well. It has a straight-up flue in the center of the house, is mostly protected from the outside air, and the draft has been fine. My wood is red oak, verified at 14-16% MC. I have had no problems with difficult starts, back puffing, smouldering, etc.

But keeping the stove at 550+ overheats the room and is eating up wood, even with the air turned down to about 25-33%. I think I've been blasting away too much, in an effort to avoid the dreaded dirty flue.

 

[begreen]

Once the wood is fully charred and in the coaling stage all the volatiles have been burned off. At that point no creosote producing gases are present.

Add less wood and burn smaller fires if the temps outside are mild and let the fire go out.

 

[Sparky31]

Thank you BeG. I recall that you used to run a F400. Did you have to keep it on the upper end of hot to get the secondaries working?

 

[begreen]

Thank you BeG. I recall that you used to run a F400. Did you have to keep it on the upper end of hot to get the secondaries working?

Our F400 would heat up pretty quickly if I placed a pair of 1-2" sleepers N/S under the E/W loaded wood. That allowed boost air to get under the wood and start it quickly. On a good day I would be starting to close down the air in about 10 minutes and the secondary show would begin with a stove top temp of about 350-400 if this was a cold start. I have found that flue temps are more important than stove top temps for determining when to close down the air. With a probe thermometer I now start shutting down the air at least partially with a temp in the 400º range.

PS: It took me a couple months to really get used to running the Castine. My initial start up times were more like 35 minutes.

 

[SpaceBus]

I feel like I obsess over stop top temps too much and I should really only be looking at the flue. Especially since my stove manual doesn't mention stove top temps at all. I'm paranoid of over firing the stove. Maybe I should take the stove top thermometer off.

 

[begreen]

I feel like I obsess over stop top temps too much and I should really only be looking at the flue. Especially since my stove manual doesn't mention stove top temps at all. I'm paranoid of over firing the stove. Maybe I should take the stove top thermometer off.

Actually both are good and helpful. In our normal mild weather I go almost exclusively by probe flue temps but when it gets cold out and I am pushing the stove harder I also watch the stovetop temps. The most important instrument though is one's own senses. Your eyes, ears and nose will tell you a lot about how the stove is running and when it is getting very hot.

Your Morso flue temps will be lower than some, but important. Don't worry too much, it's a well-built stove. If you keep the stovetop below 800F it will be fine.

 

[SpaceBus]

Actually both are good and helpful. In our normal mild weather I go almost exclusively by probe flue temps but when it gets cold out and I am pushing the stove harder I also watch the stovetop temps. The most important instrument though is one's own senses. Your eyes, ears and nose will tell you a lot about how the stove is running and when it is getting very hot.

Your Morso flue temps will be lower than some, but important. Don't worry too much, it's a well-built stove. If you keep the stovetop below 800F it will be fine.

At the time of purchase I didn't consider all of the benefits of double wall pipe, but now I really wish we had just ponied up the extra but of cash for it. I've mostly been watching the firebox for exactly what you mentioned earlier on this thread. Thank you for the advice, it does help put me at ease. I've been checking out the flue and firebox since we have a short reprieve from winter today.

 

[begreen]

No problem, it's an easy retrofit. When you switch to double-wall also order a Condar probe thermometer. Between the two thermometers you will learn a lot about how your stove performs under different conditions and with different fuel loads. In the meantime you can occasionally move the stove top thermometer and place it on the flue right above the stove just to see what normal surface flue readings are like.

 

[SpaceBus]

No problem, it's an easy retrofit. When you switch to double-wall also order a Condar probe thermometer. Between the two thermometers you will learn a lot about how your stove performs under different conditions and with different fuel loads. In the meantime you can occasionally move the stove top thermometer and place it on the flue right above the stove just to see what normal surface flue readings are like.

I have a condar stove top and a condar flue surface thermo. Our chimney is a little big for this stove with 7-8" square flue tiles. I thought double wall was just for clearance. If I had known this stove would be difficult to keep surface temp around 300 and keep the stove top under 700, I would have gone with double wall to start. The sales guy didn't include anything about that, and there weren't any reviews on the 2B Classic when we bought ours. I'm also planning on putting a 6" liner, probably insulated, inside of the clay tiles.

I just checked up the clean out, and it doesn't look much different from when we started burning in November with the old Defiant. There's possibly some glazing, but we also don't have a cap, so it could be water. I took the baffle out of the stove and checked the heat exchanger, so far just some soot and fly ash. I guess I'm doing something right!

 

[begreen]

Yes, issues with creosote should become a thing of the past once you have a good liner and double-wall installed and as long as the wood is fully seasoned.