7" rebuild - replacing IFB

Hello all Rocket Stove builders!

I am going to share an experince basically for one reason and that is simply to tell the good and bad of my past few seasons of the 7"  batch box build.

The good: It worked right out of the gate on the first burn and nearly every burn after,  easy to light, easy to clean and it simply worked.
As most of you that may have followed my various suggestions on stove building, I was and still am pretty insistent on building to the KNOWN working numbers.  (for both the stove and bell)   I don't have any experince with ducted benches thus I never comment on them.

Make no doubt about it, I have relied heavly on the advice of Tom of Dragon Fame. Fox James and his great experiments and of course Peter van den Berg  who without him I might be still rubbing two sticks together.

The bad:  Late last season during my monthly inspection I noticed a piece of IFB laying on the inside floor of my bell, but all was working well so didn't think much of it, later I found another  and this kept going... but all was working so I was only puzzled.

So finally on 9/25/2026 I took off the face plate of my bell, (very easy to make, worth every bit of time to construct, as with it off I can crawl right in if need be)
and what I found was very simple, anything I built with good hard fire brick was perfect, anything I built with IFB (Simon Brand) which was all of the riser and some re-enforcement pieces was simply junk, (cracked, broke, or completely out of place)  I doubt I will ever use those again. If I feel something needs extra insulating power, I can always add some of the Mineral wool, or many other product out there that seem to hold up well if this don't have to touch the wood.

I am sure other bricks might stand up better, but I am never going to take the risk again.

So now the really good.  Everything is repairable, (replaceable) the bell is in great shape, and the mineral wool inside was good too. Without the large face plate this would require reworking the bell to some extent, (never fun) This is not bad.

Final explanation of the breakdown of the IFB's--- This stove is run hard, I can often heat a 1/2" dia  (12-14mm) metal rod to a glowing red in less than 5 minutes and just guessing, the IFB's even though they were rated for extreme temps, simply did not hold up. Perhaps even shifting slightly during heating phases. Again, I don't know for sure, and I don't really care now, as the riser is completely out of the bell in 30 minutes of time, and the rebuild will take place.

WARM regards to all.

I already commented on this issue stating that there exist quality differences between various IFBs, but now I'm thinking that they should not be used in the wood flame path.
Two vendors/manufactures that I inquired about IFB use in flame path said it was OK, but at the same time it's rather obvious that they are not intended for wood flame path:

1. IFBs are rather new invention, established in industry in the 50s.

2. Industry uses natural gas, propane or electricity to melt, crack, kiln fire.

3. If wood is burnt in biomass power stations or incinerators - high alumina hard bricks are used (I read some paper), because amount of fluxes and detrimental substances is high.

My electric ceramic kiln is lined with IFB-26, but it's electric and only I converted it to propane and propane exhaust is super clean compared to wood and I use it maybe 10 times per year only, so I may not be able to notice any deterioration.
I just read that IFB/propane kilns may have longevity of 1-5 years in high use environment. High use for ceramics firing would be once per 3 days, because cooling to less than 50 C (safe for glazes) takes me around 40 hours. For quick raku firing (objects are removed hot from the kiln) firings could be more frequent with much more thermal stress.
Masonry heater will be probably fired for let's say 4 months, so with one fire par day it's 120 firings - equivalent to once per 3 days kiln use schedule. However the fuel is wood with chlorine (bricks don't like it) and various fluxes. Also the temperature in properly built riser is equal and turbulence much higher than in a kiln.

So it looks like IFBs in wood flame path are really being tested by us. I'm really curious about performance of IFB risers built by others.

Cristobal Cristo wrote:I already commented on this issue stating that there exist quality differences between various IFBs, but now I'm thinking that they should not be used in the wood flame path.
Two vendors/manufactures that I inquired about IFB use in flame path said it was OK, but at the same time it's rather obvious that they are not intended for wood flame path:

1. IFBs are rather new invention, established in industry in the 50s.

2. Industry uses natural gas, propane or electricity to melt, crack, kiln fire.

3. If wood is burnt in biomass power stations or incinerators - high alumina hard bricks are used (I read some paper), because amount of fluxes and detrimental substances is high.

I remember and fully agree now.  This is one of the reasons for my posting of the final results as they have often been recommended to use in locations just like I did.  I am not blaming a soul, just reporting the end results after 3 years of hard burning.

Cristobal Cristo wrote:
My electric ceramic kiln is lined with IFB26, but it's electric and only I converted it to propane and propane exhaust is super clean compared to wood and I use it maybe 10 times per year only, so I may not be able to notice any deterioration.
I just read that IFB/propane kilns may have longevity of 1-5 years in high use environment. High use for ceramics firing would be once per 3 days, because cooling to less than 50 C (safe for glazes) takes me around 40 hours. For quick raku firing (objects are removed hot from the kiln) firings could be more frequent with much more thermal strees.
Masonry heater will be probably fired for let's say 4 months, so with one fire par day it's 120 firings - eauivalent to once per 3 days kiln use schedule. However the fuel is wood with chlorine (bricks don't like it) and various fluxes. Also the temperature in properly built riser is equal and turbulence much higher than in a kiln.

So it looks like IFBs in wood flame path are really being tested by us. I'm really curious about performance of IFB risers built by others.

Excellent deduction for the cause of the problem and end results. While no one has asked, this was not a expansion limiting layup of bricks. Unless they could have walked, I will never know now. But I am doubting it, as the perfectly undamaged bricks were just below and besides the IFB's

Thank you Cristobal Cristo for possible root of the cause.   I would like to add one thing concerning propane heat, and cinder block only flues using standard mortar,  this has been known to cause problems. Though I am not sure the root of the cause. Some flues, as in my case, had cast high clay liners that are working just fine after 67 years,  (no propane every used, simply wood stoves all these years)

regards
Scott