Proper Wood Stove Flue Use?

[EastoutWest]

Wood stove exhaust damper/flue use, am I doing it right?

My flue method: exhaust damper fully open when starting a fire and until I have a decent bed of coals, then fully closed. Open it whenever I add wood so I don't get smoke in the house. If there is still a decent bed of coals I generally close it fully. In my mind's eye, a closed exhaust flue will decrease heat loss up the chimney, increase firebox temps and improve secondary burning (so optimal when you are trying to maintain heat/efficiency). Adversely, an open flue will increase exhaust/chimney temps, therefore increasing draft (so optimal when trying to start or rebuild a dying fire but at the expense of burning efficiency).

This method is mostly based on my experience with an idiotic cheap EPA wood stove that has no intake control/damper (just 7 ports over the door, wide open all the time). I have recently "upgraded" the stove with tin foil intake port covers (that stick in place using firebox suction). It's not optimal but it works ok. The above flue control method has been the best method for me in the past but is there anything I'm missing now that I can actually restrict my intake air? If the intake air flow is restricted, does the exhaust damper position even matter? Or will restricted intake + open exhaust still allow 'heat waste' up the chimney?

Thanks in advance for your insights!

 

[SS396driver]

Air coming in restriction works better than a damper . I looked at your stove in your other thread something like this may work better I made this for the smoker I built . Looks like you could make something like it

 

[EastoutWest]

@SS396driver cool! I've considered doing something like that and have the tools to fabricate. Could just be like adding a slide channel just under and above the ports then using a piece or two of thick scrap sheet metal with a handle to slide in and cover the ports. Probably one from each side so the intake air can enter from the center rather than one side. Edit* The ports are too wide and close together to use a traditional overlap design like in your photo (unless it slid up and down, which isn't really possible due to the proximity of the door and angled shelf overhang).

My current favorite idea is to slot a 1"-2" tube so it opens to the intake ports and weld it to the stove (made of sheet steel, not cast iron), then close up the open ends with some kind of valving or even the screw-type intake dampers you find on sealed wood stove doors. Either that or seal one side of the tube and valve the other with plumbing for fresh air from the brick chimney (it has a flex liner inside).

A third option may be the simplest but not ideal to me because it replaces the pretty glass with 1/4" sheet metal with an intake damper like you've made. I would have to seal up the original intake ports but in theory, the glass could be put back in if I so choose. I do like seeing the flames and feeling the radiant heat through the glass though.

 

[SS396driver]

Simple flap door most likely two to cover the holes with some way to open and close in small increments

 

[TimberWolf530]

" In my mind's eye, a closed exhaust flue will decrease heat loss up the chimney, increase firebox temps and improve secondary burning (so optimal when you are trying to maintain heat/efficiency). Adversely, an open flue will increase exhaust/chimney temps, therefore increasing draft (so optimal when trying to start or rebuild a dying fire but at the expense of burning efficiency)."

Your thinking is actually backwards. Think of your stove as an engine. It needs proper intake AND exhaust to run properly. Just like an engine, the more fuel and air you run through it, the more power (heat) it produces. Choking the air intake or exhaust makes it run more inefficiently, and cooler. An unrestricted flue is necessary to create a proper draft. The draft pulls air into the stove, and pulls smoke and gasses (Carbon Monoxide) up the and out of the house. It also allows you to maintain heat in your flue that is necessary to prevent creosote build up. If you run a cool flue, leading to creosote build up, you run the risk of chimney fires. You should control temperature of your stove by changing the amount of air going into the stove, not by blocking that trying to get out. Improper draft also risks the building up of carbon monoxide inside your home. If you open up the flue damper, you'll maintain proper flue temperature and allow poisonous gasses to be pulled out of your house. Finally, everyone that has a wood stove in their home should have a properly functioning CO detector in addition to smoke detectors.

 

[EastoutWest]

Your thinking is actually backwards... You should control temperature of your stove by changing the amount of air going into the stove, not by blocking that trying to get out.

I appreciate the response. It makes sense but has me wondering what the purpose of the flue damper is then.

Since I don't have any intake air control other than tin foil, it is difficult to maintain the ideal intake volume consistently. It blows my mind that any wood stove manufacturer would release a model that has no intake control (I didn't buy the stove). Except when my chimney cap was sooted up from wet wood last year, closing the flue has never restricted flow enough that smoke comes out of the intake. For times when the fire is burning so intensely that it creates a sort of fire-buffeting, I have observed that closing the flue slows the burn down just enough to stop the buffeting (by which I mean the fire pulses in intensity). I have also observed that with the flue open, the fire sometimes exhausts too quickly to maintain the secondary burn but closing the flue immediately causes that good ole efficient plasma effect in the firebox. I'll have to try keeping the flue open and tin foiling the intake to reproduce these situations.

I am quite familiar with internal combustion engines and see the comparison but will point out that an engine's combustion chambers are not open to the atmosphere like a wood stove; they are restricted by the valves to create pressure for combustion. Only by closing/pressurizing the combustion chamber can you keep the fuel in and ignite it efficiently enough to turn the engine. So then, in theory, if you restrict the flue, you keep wood-gas vapors in the firebox longer, giving them more time to be burned? IDK but I suppose restricting the intake would probably have the same effect because exhaust can only go up the flue as fast as its replaced by fresh air. Totally not trying to argue with you, just trying to explore theories. Most people I've seen talk about flue use do leave it open and control temp with air intake. The tin foil allows some level of that and I'll try to change my habits developed over the past several years without intake control.

I do have a CO detector and it has only read over 0 ppm once or twice in the past 4 winters (it has a peak value reading).