Wood stove fire chamber insulation? Not sure I get it

I heard there was no such thing as stupid questions, only (you know the rest) Ok, so lets test that.

I've had many new off the shelf and used wood stoves over the years, both insert types and freestanding in well insulated modern homes. Just bought a mountain smallholding (homestead) with the usual (for this part of the world) 3 foot thick stone walls and no insulation plus very cold solid floors. So looking to get the most from my wood burner. Property came with a badly fitted Jotul 3 with no internal insulation (fire brick lining). Trying to work out whether it's worth getting some. What I don't understand is that I thought stove bodies got hot and radiated heat, so why fit fire brick insulation. Seems like insulating steel outer from the fire would reduce heat radiated this way resulting in more lost up the chimney. However  there is obviously a reason everyone does this, so I'm clearly missing something. Would love an explanation if you can. Obviously we are working on insulating the property itself and playing with thermal mass but feels like there could be a win here. Any thoughts?

Thanks (Diolch)

High quality, efficient wood stoves are engineered as a sum of their parts. These materials work together creating a safe and efficient combustion system.

I find that the fire bricks keep the combustion chamber much hotter, so it's easier to add fresh wood to the coals and have it roaring hot and burning clean in no time. The fire bricks aren't insulation like kiln bricks, they are thermal mass that holds heat.

I have also used welded back-yard stoves. The plate steel cools off so quickly that I end up making fire from scratch half the time, and there is lots of smoke. This is not a good way to heat a house.

Removing the bricks from a stove designed for fire bricks is not wise. The firebox could warp, the safe clearances will change, and the combustion efficiency will likely be affected.

On the other hand, adding fire bricks to an efficient stove not designed for them is not a good idea either. It may cause damage. (This probably doesn't matter on a home-made stove.)

Is this the stove you have? I don't see any reference to fire bricks in the manual or expanded parts drawing.
https://www.jotul.com/products/wood-stoves/f-3-cb

Thanks for the reply Douglas. It is a version of that stove but without the ash pan. It has separate metal plates inset  from the sides  approx 2"  which look like they give some shielding to stop the sides cracking. There never has been fire bricks in this particular stove, so perhaps they wouldn't be much help. The reason for the question in the first place is that I have been looking into building an RMH where the insulation on the riser makes total sense as the heat leaving the unit gets used in the mass structure and not just chucked out the chimney. I had wondered if the firebricks serve as a thermal mass and more of a heat shock defense, still allowing a good amount of the increased heat in the firebox to radiate through the sides. I've built a freestanding foil backed stone tiled dense block wall around the back and sides of the fire so that heat that comes that way is absorbed and radiated into the room long after the fire dies, rather than leaked straight out through the back wall. So I'm keen to get good radiation on 4 sides. Any suggestions would be great.
Cheers

Douglas got most of the list of the reasons for firebrick liners.  One other.

1.  Over time the hot spots in the stove slowly oxidize the steel and it burns thru.  With fire bricks this can't happen.  Also by even distributing heat there is less stress on the steel also making for stronger more air tight fireboxes.

^^ Yes, absolutely. Well said!

Manufacturers of well engineered stoves often have an inventory of brick kits, which of course ablate and spall over time under hard use. Often you can find a kit for a 20 year old stove because, naturally, it's still operational -- it just needs a little love. And new bricks.

Ok I've done some research of my own.

-Fire bricks poor thermal mass which is better off in the room than firebox .
-Insulation/Shielding is more a way of evenly distributing rather than stopping heat transfer to outer case (no hot spots)
-Hotter burn smaller fire uses less wood.

I think I get it.

Sounds like a good plan, but as I'm hoping to replace the stove soon with RMH and as Douglas suggested, not designed with them I think I'll leave it with steel plates and deep bed of ash for now. A Yorkshireman of Scottish descent living in Socialist Wales, as you can imagine short arms , deep pockets is an issue.

Thanks for the advice it's going to be of graet help going forward.

Last thought, I've underestimated the thermal mass properties. While this type of thermal mass would not be great for floor slab construction, due to it's lower density and higher conductivity, this is what makes it work in this setting.  Helping the stove burn hotter and cleaner and to build heat in the box while allowing it to conduct evenly to the shell without distroying the metal. So of real benefit to the person trying to heat their house.
Still want to sort out the heat loss up the flue but that's a different problem and doesn't reflect on the fire bricks.

Wow, get it, love it.

Learned to read posts more carefully. I think that's pretty much what Douglas said in his first reply. I am wondering though whether I need a mass less conductive for the riser in my future RMH. One for a different thread I think.

Thank you all, it's been a very useful journey.

A riser in a rocket mass heater needs to be as lightweight and insulative as possible. It needs no real abrasion/impact resistance; The stress is all from heat and moving air.