Adding a bell/bench to the flue path of a standard box stove

[DCish]

So, after a week of testing, here's how it's shaking out. Light a hot fire, flip the dampers, and flue gas runs through the bench as planned. Bench is an open bell roughly 14" x 15" x 64" internally. Walls are 2 bricks thick, ~6" on the sides, 5" on top (until the top cap is on, a slab of 1" slate). Heat travel is about at the rate expected (~1hr per inch, or ~5 hrs of run until heat is felt). Max temp on top so far is about 100° near the flue entrance and on average 15° less at the far end. Flue temp after bench is a pretty stable 200°F by probe thermometer even as input temps range between 700° and 300°. I suspect is stays this high because of leakage around the damper, which isn't designed to fully close.

I'm pretty happy overall. This is intended as an iterative project with the next step being a 6" PBB which will be refined outdoors before eventually replacing the current commercial stove. For just this stove it would be overkill, the fact that it only ever gets to 100° even when run flat-out for hours makes that clear.



EDIT: Original "slateless" photo lost when Google+ shut down.

[matthewwalker]

Cool DC, neat little proof of concept project there. It looks pretty tidy as well, nice job.

[DCish]

Thanks Matthew! Can't wait until I get all the little details sewn up.

[ericvw]

I definitely dig it DCish !
Like Matt said, nice and tidy, too.... Very impressive build- betcha can't wait to mess with the batch box; truly amazing burner. None of us can thank peterberg enough for his time and attention to every last detail in refining the batch box! One of the greats, he is! 
Eric VW

PS- where do you source your firewood from?

[DCish]

Thanks Eric. The "tidy" part is due in no small part to the WAF needs of the space, but I do like to have me some clean right angles when I can... As for wood, I live in a suburb that has a lot of mature trees. After every major storm there is damage and crews are out cleaning up, sometimes taking down entire trees. So I just offer to let them dump the burnable lengths in my driveway. They jump at the chance to save the time and fuel of running to the dump, and voila, a year's worth of wood! Then I spread out my exercise over a few weeks with a maul, and presto! Takes up a good chunk of the yard, but I rather like that look... and I feel so good about taking something out of the waste stream and making good use of it. The bricks came the same way, something someone was getting rid of.

And yes, very excited for the batch box, so grateful to Peterberg! Hoping to use an S channel for secondary and play with some alternate riser configurations... great fun! My hope in the end is a burn cycle much like what MatthewWalker gets, a nice long burn with very low primary air giving me some good steady heat while I load up the bench, then have the bench hold heat while I'm out of the house and the fire is out.

[DCish]

Slate on. Still need tile around the base and by the inlet/outlet, but no rush on that.


Definitely proving itself as a part of the house and the household.

[ericvw]

Definitely Sweet, DCish!
Kids look to be benefitting from ur hard work, too! U sure you don't live in Greenbelt?
Eric VW

[DCish]

Hah! No, but it sounds like you're familiar with some of the cultural nuances of the area! Not Takoma Park either...

[ericvw]

@dcish,
Don't know about Takoma Park, don't really know much about Greenbel eithert, but a friend of of the family lives there(Greenbelt) and his kids look like yours! Thought maybe you were him!
Eric VW

ps- why, when I put a "circa/at" in front of your user name, does it change capitalized DC to lower case? Wierd stuff...

[DCish]

Gotcha. And no, no idea about the capitalization thing

[patamos]

Nice work DCish

When you run the stove for 5 hours do you have full O2 supply with multiple reloads? Or slower gasification of fewer loads?

Re the non closing damper. An idea (i have not yet tried) is to take a 7" cast iron damper plate and grind the perimeter down to 6"

[DCish]

Feb 15, 2015 10:23:45 GMT -8 patamos said:

When you run the stove for 5 hours do you have full O2 supply with multiple reloads? Or slower gasification of fewer loads?

Re the non closing damper. An idea (i have not yet tried) is to take a 7" cast iron damper plate and grind the perimeter down to 6"

Thanks Patamos!

Regarding length of runs:
With lower stack temps and more elbows in the run, draft is lower, so full O2 isn't quite like running full O2 was before. This being a soapstone stove, I have to run an entire load of small splits (~1-2") loosely stacked just to get it up to temp (about 15 min). If I'm careful then I can load a few full-size splits, get them established, then get the whole load going. After it's going another 10-15min, then that batch is in gasification mode and I can knock back the air to about 1/4 to keep initial flue temps at 600F. If I let flue temps sustain above that level the surface of the stove goes above the manufacturer recommended 500F and there is risk of damaging the stove. This is how I try to set it up when I'm bedding down for the night. It'll leave me a solid bed of coals 6 hrs later when I get up and build again as needed based on weather conditions. With the single digit lows and high winds the last day or two overnight it struggles to keep up with things (1200 sq ft house, attic wicked insulated, walls not so much, target temp 63-65F on main of 3 levels in a split-level), but it does fine down to the teens, especially if it's sunny during the day.

I can run the stove at a cooler level, say 400F, and it'll burn fine and apparently just as cleanly (by smell, anyway). Heat will still get through the bench in 5 hrs, it's just that bench temps are lower (say 80F rather than 100-120F).

I toyed with the idea of getting the damper to fit tighter, but after testing it, I found that stuffing the holes with ceramic wool and gluing it in place with sodium silicate was good enough. I need the leakage around the outside to keep the flue at the minimal 200F needed to run the chimney, and I know that from a safety standpoint, with that outside gap nobody can accidentally turn the damper closed and cause an unsafe smoke or CO backup into the house. As stove temps fall and draft falls, it seems to stop drafting through the bench and just eeks by the loose damper, so the bench doesn't cool unduly quickly.

[DCish]

Update... took some time at the start of this season to seal all the 16 joints between the flue bits with a mix if fire cement and ceramic blanket. Now I can run the flue gasses through the bench starting at much lower temps and with less warm-up time. Must have been leaking quite a bit.

[dustylfc]

Have you any finished pics now ? Or video would be great :-)

This is something am concidering for outdoors but might have to go single skin to compensate

[DCish]

Nov 2, 2015 5:26:06 GMT -8 dustylfc said:

Have you any finished pics now ? Or video would be great :-)

This is something am concidering for outdoors but might have to go single skin to compensate

Huh, went back and saw that some of my links had broken. Fixed them as best I could, hope that gives you the visual you were looking for. Video is not a bad idea, I'll look into that. Also added a third thermometer the other day to measure the temp of the flue gas as it is exiting the bench but before it picks up more temp via leakage from around the damper. I haven't run it hard enough for the bench to get really warm yet, but so far it's only gotten up to 100F - excellent heat harvest! Will try to add a pic of that to this post when I can.