Hot Rodding the stove started today

[Augie]

So being an Engineer I know that there are always trade offs made during the design process. Many times in entry level consumer goods the choice is towards reliability over performance. Especially items that are meant to last 5+ years as our stoves are, I am assuming this because I have a 5 year warranty on mine. After reading here and finding a couple of white papers on combustion in residential woodstoves I have learned a few things.

First is that for secondary combustion to occur reliably you need to keep up temperatures in the firebox. Their are all couple of ways to do this, provide increased primary air, this is at the expense of burn time. The other way is to have a better insulated firebox. This is what I wanted to address. Insulating the firebox better. The Avalon Spokane/Lopi Republic uses standard fire brick. The design appears to favor durability over performance knowing insulated firebrick would need to be replaced every other year if not every year.

Detroit has a great number of companies that sprung up over the last century to service the auto industry. Among them are a few foundry builders. I have delt with one previously and called them up to grab some IFB. They were $2.20 for full brick or $1.10 after I cut them in half. After this I replaced all but the floor of the firebox with IFB. So the total cost for this idea was $16.00.

Looking forward to being able to close the primary air down sooner and even a little more than I had been doing. If my understanding of the papers I have read is correct.

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[Slow1]

Interesting - I don't know squat about IFB but it looks pretty easy to work with. I assume you are expecting it to help keep the firebox hotter - but will it allow enough heat out to actually heat the outside of the stove? I expect there is a point where you are keeping too much heat in the firebox and not allowing the stove to actually heat the room - the heat needs to go somewhere after all.

 

[Highbeam]

Augie wants a lower burn setting. This to increase burn time and lower output of the stove correspondingly. Also, since an increase in low temp efficiency may occur wood may be saved.

 

[blades]

That looks pretty close to the innards of my nc 30 ( and a whole lot of other units), IFb 2/3 way up side wall a bit on back wall secondary air preheated up the box on the back wall to the 2nd burn units across the top of the fire chamber. Can't tell type of baffle above 2nd units. My old stove late 90's had 1/2" 2000deg baffle board on top of the tubes then some space and a steel plate which formed the top of the fire chamber with a gap between it and the actual top of the stove. Fire chamber top became warped and cracked, project #11111 take apart and replace damaged area. Heated my trailer for 7 years, too small for house.

 

[Augie]

BRand New stove from Travis (lopi/avalon) it uses Firebrick above the burn tubes then a 1 &1/2 inch air space then the Steel plate for the top of the stove. Hot Exhaust Gasses are what keeps the stove pumping out heat. TO do that you need good secondary combustion.

Remember that you get most of the energy from a EPA stove by burning the gasses before they leave the firebox and go up the flue as smoke, be that with a cat or a secondary burn system. By keeping the firebox hotter, and turning the air down, you keep more of the smoke and gasses in the firebox to mix with the Oxygen provided by the Secondary tubes.

The current design of most stoves use air passages on the rear ,bottom and sides, to keep all but the top of the stove under 150 degrees for reduced clearances to combustibles. Mine is built this way as well. This means that all of us rely on the top of the stove for most of not all of the heat output of the stove. I will still have hot gasses traveling just under the top of the stove on their way to the flue and up the chimney. What Im seeking is to keep the same temps at stove top with less input of air. OR said another way I want to keep the secondaries going longer at lower air settings. The only way to achieve this is keeping the fire box hotter in effect increase the efficiency of the stove.

Insulating your fire box will actually produce MORE BTU's per given load of wood than a poorly insulated firebox. Look at the difference between the pre epa stoves and the epa stoves, Secondary air or a cat and insulating the firebox. I am just taking it to another level. If I get a 5% increase in performance for $16 I think I have made out like a bandit.

IT is a Physics and Chemistry thing. Something that I am good with.

 

[Huntindog1]

After putting 1/4" ceramic 2300 deg insulation behind my fire brick , I still get heat out the sides of my stove.
Keep us updated on what you experience. One more thing I put insulation under the floor fire bricks also.
But I think if people keep an 1" or so ash in the bottom of their stoves it should do the same thing for the floor.

I got the idea from WES999 as he had good luck from doing this also.

 

[WES999]

Good job, it will be interesting to hear how it works.
As Huntingdog said I added 1/4" Kaowool under the bricks in my stove, (my stove already has the lightweight
bricks).
I can generally run my stove with the air fully closed.

Also don't forget plenty of heat is transferred from the front of the stove.

 

[wkpoor]

Wow! Ironically me and Steve at Vermont Elm just had this identical conversation yesterday. We talked about insulating the firebox also to increase the length of time the secondaries would stay active. My one question is how durable is that product.

 

[Huntindog1]

If your insulating behind the fire brick you have the firebrick to protect the ceramic insulation. Which the Ceramic Kaowool is rated to 2300 deg F.

If you talking using Pumice bricks that are insulative, plus there are other types of IFB (insulating fire brick), Pumice bricks are not as durable as the basically have a bunch of air pockets designed into the brick material that gives the bricks insulative properties. But several stoves use them and people have had good luck with them.

You can use a ceramic coating used by the forge and brick oven industry called ITC-100. It is supposed to improve durability of what every you put it on. Plus increase the heat reflectivity of the brick as most of the heat in the fire box is radiation type. So a coating like this should be a factor. I even put it on the under side of my baffle board. The forge and brick oven operators say it increases the temps inside their ovens.

What I have noticed is if I used good dry wood the surface of my bricks now stay a nice white look with the ITC-100 coating.

 

[begreen]

Augie, can you provide a company name for the brick maker and website link if they have one? What is the composition of these bricks?

 

[Augie]

I have no idea who made the bricks, but they are a light weight ceramic. They were sold to me by a company that doesn't normally sell to the public so I am not comfortable giving out their info. Needless to say they are durable but not as durable as the oem bricks. I would think that if you went and bought IFB from your local shop ot would be the same stuff

Initial impressions are positive. I built a fire at 11pm last night and at 10:45 this morning I still had 200degree stove top temps. This is longer than usual on a not totally full load. Also I seem to be getting to a 600 degree cruise temp on stovetop sooner. This could be wood or a change what I'm doing, but for now I'm happy. We shall see how it works for the next few weeks but for now I believe that the performance is better with the IFB than without.

 

[eclecticcottage]

I'm also interested in how this works out longer term. We get pretty good burn times, but longer ones are better. These stoves don't put out a lot of heat off the sides anyway so it shouldn't effect heat output too much.

 

[Dutch]

I had the exact same intention when tweaking my stove. I wanted to increase firebox temperatures, more importantly I wanted to increase secondary air temperatures. By reducing the size of the secondary air intake port, I noticed faster secondary light off, more secondary activity, and longer burn times. The theory is that the longer the gasses reside in the secondary manifold, the hotter they will be.

 

[Augie]

So after a few days I have learned somethings

Adding IFB has allowed me to run lower primary air and smaller loads but still get stovetop temperatures above 600 and good burn times 10 ish hours.
I don't have any way to verify this but I think I have increased the efficiency. I notice less smoking and smaller amounts of ash in the stove.
I would suggest that anyone with a Lopi/avalon should think about this mod.

 

[begreen]

Thanks for the update. It seems to verify my guess about why PE and Quad chose to use premium pumice stone firebricks in their stoves.

 

[ailanthus]

I'm really interested in your on-going observations from this. In my case, the stove is a bit undersized, so in the coldest months I never let the temperature get too low, so I don't think IFB would provide much benefit (possibly even detrimental??) during those times. But for these months where I'm constantly starting fires & letting them go out, I definitely could imagine that it would help. Not that this type of mod would even be an option in a Castine since there's no exposed firebrick, but still interesting to think about.

 

[EatenByLimestone]

It seems to me that, baring looks, you could wrap the outside with a kaowool blanket and hold it on with magnets. This would hold the heat in the sides during the shoulder season and you could easily remove it for the main heating season.

Matt

 

[Huntindog1]

This has been pointed out previously , that some stoves have heat shields on the sides from the factory. I really think these free standing type stoves are designed to radiate most the heat out the top plate and front. As the hot gases proceed towards the front of the stove and up to the top and out the flue.

 

[EatenByLimestone]

I wonder if covering too much of the outside might severely limit what comes out of the stove and the life of the stove.

I keep thinking of the old Jotul Combi stoves and how they used lots of size to suck heat out of the fire and radiate it out. Stoves are now much smaller so they have less area to radiate the heat. So each side would be hotter for any given size fire. The firebrick knocks down that area even more. Tweaking heat output on the sides does it further. Most of the sides, the back and the bottom aren't radiating heat like the old stoves did. So the top and front are doing extra duty. I wonder what the long term consequences of forcing all of the heat out of 2 plates is? It might make more sense to focus the heat down into the burn chamber from the top than to reflect it in from the sides.

Just brainstorming,
Matt

 

[Bub381]

I fully loaded my Fireview at 9:00 pm and never reloaded the next day till 9:00 pm and still had a stovetop temp of 120 . It was a warm 30's to 40's day and also a test.Just giving you a soapstone comparison.

 

[eclecticcottage]

Hm...I guess I'll have to look for a place that sells them.

 

[Bub381]

There's only 1 place that sells them.http://www.woodstove.com/

 

[Huntindog1]

I wonder if covering too much of the outside might severely limit what comes out of the stove and the life of the stove.

I keep thinking of the old Jotul Combi stoves and how they used lots of size to suck heat out of the fire and radiate it out. Stoves are now much smaller so they have less area to radiate the heat. So each side would be hotter for any given size fire. The firebrick knocks down that area even more. Tweaking heat output on the sides does it further. Most of the sides, the back and the bottom aren't radiating heat like the old stoves did. So the top and front are doing extra duty. I wonder what the long term consequences of forcing all of the heat out of 2 plates is? It might make more sense to focus the heat down into the burn chamber from the top than to reflect it in from the sides.

Just brainstorming,
Matt

As far as being to hard on a stove:
Well since most the time people are operating the stoves at their lowest setting , dont think its too hard on the stove,

If your a person that runs your stove wide open all the time then it would most likely be an issue.

 

[Huntindog1]

Hm...I guess I'll have to look for a place that sells them.

Fireviews are really nice stoves , I would have loved to had one. At $2500 its a pretty good chunk of change.

At the time I was getting back into wood stoves I was just looking for some extra heat for a new family room in the basement.

Went to the local Menards and got my Vogelzang on sale for $600 , then realized the dang thing was able to heat my entire house, thus I am completely back into wood burning.

I save around $1200 to $1500 a year in all electric heating costs.

One of these days I am going to have to try out one of those Cat stoves.

 

[eclecticcottage]

There's only 1 place that sells them.http://www.woodstove.com/

Thanks. We'll look into it for next season since I don't really feel like letting the stove cool that far down this time of the year :D I am thinking maybe just do the sides/back (and maybe the bottom to help hold coals longer) and leave the top with the standard bricks since it heats mostly off the top and front due to the side shielding anyway.

I wonder if it will effect the burn tubes eventually if you swap out the top bricks since you're holding more heat in right above them.