Woodstove mod part 7, Two Ceramic fiber boards with secondary air or S-valve as "after burn" design

 

So I insert the two ceramic fiber boards and in the back wall I put in a couple other smaller 

ceramic fiber boards to hold in the 90 degree elbow secondary burn stainless steel pipe. I add some side

wall ceramic fiber boards to hole up the 2nd ceramic board baffle. The first ceramic board is held up

by the steel baffle. 

So the extra oxygen will then burn off the gas as the two ceramic fiber boards heat up.

 

I will leave the back space open - as the stainless baffle currently does not close off the back space.

The hot air secondary air will then suck the smoke up through the back and between the ceramic

 fiber boards to burn off - and then to the front of the baffles - and up and over and back to the collar

 exhaust exit at the top of the stove.

 

That forward and up smoke exit due to the secondary air pulling in the smoke through the back 

will then cool off the smoke before it exits the stove - so that the top steel is not too hot.

 

Since the front space will be left open then the primary air can still exit via the front but since the

 back secondary air will be extra hot then it will suck the smoke to the back - thereby preventing 

any front draft going out of the front of the stove when opening the door.

 

As the stove currently operates there is not enough oxygen in the back of the stove for a clean 

burn and the front of the stove is too cool for a clean burn. So this will solve both problems by

 heating up the stove more and providing better oxygen in the back.

 

The problem with the ceramic fiber board on top as the baffle is that there is smoke forced to the 

front of the stove so that when opening the door there is back draft and smoke coming back into 

the room.

So by leaving the back open, as is currently designed then there is no smoke. By preheating more

 oxygen to the back of the stove that will pull the smoke back and up between the ceramic fiber 

board for a clean burn.

 

 

So there's the baffle in the top of the stove. I need at least two inches of space between the baffle

and the exit stove collar flue

This shot shows the flame being sucked into the exit collar flue as the flame goes around

the baffle. (vid link) Looks like a 3 inch space.

 Lesser drafting with a larger diameter or no insulated flue requires more opening above baffle. So start low with larger opening and raise with set bolts to no less than the same opening in square mm as outlet. You want to be able to fine tune it for your fuel and chimney....the baffle was designed to reduce smoke from 60 grams to 6 for every kilogram of wood burned...But the smoke particles that were present without baffle are greatly reduced by 10 times. So a slightly cooler flue does not necessarily mean more creosote when you are burning the excessive particulate.

There's probably only room for ONE ceramic baffle on top of the stainless steel baffle....

 

 

 

 There's a shot I took when I unboxed it.

 

 

 

 So that's the actual collar flue exit at the top of the image in the back.

 

 

 

 I might be able to squeeze two ceramic boards in there - but it would cut off the draft too much for when 

 

starting up the stove before it gets hots.

 My thinking is that without the baffle the stove is ~40% efficient. Adding the baffle maybe brings it up to 50% and the baffle + secondary tubes is up to maybe 60% efficient if done well. With insulating firebrick and blanket on top of the baffle maybe 65%?

 here

The stack temp becomes much more stable with baffle. They tend to run away without baffle.

 My thoughts on a homemade baffle would be to make a flat horizontal plate (5/16" thick) supported just under the flue outlet, tight against the rear of the stove to about 3/4 the way toward the front. This would be like the design used in the UPLAND. A proven design that used a baffle above the fire to force the rising gasses to move TOWARD the air intake to get above the baffle and out the flue. The Upland had the air intake on a side door, making the firebox long and deep like the Papa Bear. This reverse burn method (burning towards the air intake), against the natural draft direction prolonged the burn to create a good bed of coals and would have been my favorite stove had they ever been made with steel plate! You do have to burn this type a little differently. You end up with LOTS of coals, so you push them toward the back of the stove. Then fill it up with logs and as it burns near the back of the stove, you'll notice how the smoke has to come toward the air intake in the front to get out. It needs to make a U turn around the front of the baffle to get to the flue. The flow of air coming in prevents this, so you get a long glowing burn that is hard to beat.

 https://www.hearth.com/talk/threads/fisher-papa-bear-need-baffle-info.54217/

  Also when the door was opened, cool air wouldn't rush in and hit the flues to chill them causing contraction and leaks. 

My stove had an 8in flue collar which has an [Circumference] area of 50.24 inches. When designing my baffle, I kept the area that the smoke could move around the front of the baffle at roughly 55 inches so that more smoke could get around the baffle than could leave the stove. By doing that, I never had any smoke come into the house because of the baffle and could still run the stove as a fireplace w/ the screen that I had.

 So I have a 5 inch flu but it expands to 6 inch and goes to only 30 degrees - slowing down the velocity...

 So 40 square inches? 

 So basically cut down the back SIDE bricks at a 45* angle.

Secondary Air tube secret:

  Once the walls become heated up by the fire inside the stove the air between the walls will expand due to the heat and move upwards.