Stove interior: vermiculite versus steel?

[rickj]

If the proper way is to first have a layer of ashes and have the logs and fire on top of that, do I understand correctly that a woodburner should NOT allow air to flow from the bottom into the fire chamber? I ask because I’m looking into a stove where you can choose between A. bottom plate massive 20mm flat steel with ashpan and cast iron grate, or B. ceramic (vermiculite). My preference was the steel bottom with grate, mainly because I’m worried about damaging the vermiculite. Same goes for the sides and back plates, you can choose either vermiculite or ribbed steel plates. I would prefer steel because it is not easily damaged, while vermiculite cracks.

Another matter is efficiency, the stove manufacturer mentions in its manual that a steel interior gives a higher chance of a dirty glass. That is because with a steel interior the temperature inside the stove may be a bit lower. I asked them the difference in temperature/efficiency, their answer was that vermiculite mainly helps while LIGHTING the fire, but that later on it does not really matter. They say a steel interior is about 2% less efficient than a vermiculite interior. Would you agree?

If the proper way is to first have a layer of ashes and have the logs and fire on top of that, are a grate and ashpan to be avoided?

Thanks for any insights!

 

[kborndale]

Wood stoves normally do not have grates in them. Many people just let the ashpan fill up and leave it. They are a common source of air leaks.

 

[Wisco Shepherd]

I don't have an Ashpan but the seem to be a bit like timeshares. Seems like a good idea then you don't use it and end up just having one more thing to keep up on maintenance with (air leaks). Id just go vermiculite.

 

[begreen]

Wood fires are fed air from the top. A stove with a bottom air feed and grate is most likely a multi fuel stove designed to burn coal or briquettes.

Steel stoves usually have firebrick containing the actual fire. Some use pumice firebrick for better insulation. I prefer that to vermiculite side panels as they are generally tougher.

I'm confused by the vermiculite panel used on the stove floor. That material is often used for baffles, but I wouldn't think it tough enough for a firebox floor. What stoves are these?

 

[rickj]

I'm confused by the vermiculite panel used on the stove floor. That material is often used for baffles, but I wouldn't think it tough enough for a firebox floor. What stoves are these?

Two inserts that I like: Optimum by Metalfire:

Metalfire: https://www.metalfire.eu/en/products/wood-fireplaces/optimum

And the Kalfire W models:
https://kalfire.com/wood-fireplaces/customization-and-features
What they call “Skamol” is vermiculite. The other options are steel panels.

For both brands it’s not just the baffle plate that is vermiculite, but the whole interior.

I just moved to a house with a 20 year old insert by Rocal (Spanish manufacturer), 72x48 cm, the bottom is made of steel with two small closed ash pans, the side panels, back and top baffle are made of vermiculite. All cracked.

 

[begreen]

This board looks like Skamol ceramic which is a refractory cast composite using vermiculite, but much tougher than the baffle boards. Even though it is tough, if one slams logs into the sides or back, eventually it will crack. It is not as strong as steel in that regard.

The Optimum looks like it has an insulated fire chamber, but with the insulation behind the steel. That is a more durable construction and looks to be the more efficient example. The Kalfire looks like it is more designed for visual appeal, and less for the heating efficiency of the fire. I'm seeing these inserts for the first time so that is just my initial internet viewing impression.

 

[rickj]

This board looks like Skamol ceramic which is a refractory cast composite using vermiculite, but much tougher than the baffle boards. Even though it is tough, if one slams logs into the sides or back, eventually it will crack. It is not as strong as steel in that regard.

The Optimum looks like it has an insulated fire chamber, but with the insulation behind the steel. That is a more durable construction and looks to be the more efficient example. The Kalfire looks like it is more designed for visual appeal, and less for the heating of the fire.

I will inquire and report if the steel panels have insulation behind the steel, as far as I know now there is none. See attached pic (Metalfire), apparently any combination of panels and vermiculite/skamol is available.

 

[begreen]

The Optimum literature indicates:

A. insulated combustion chamber available with Original, Round, Triangle or Ceramic interior finishes​

It's also catalytic which should make it a cleaner burning insert.

 

[rickj]

The Optimum literature indicates:

A. insulated combustion chamber available with Original, Round, Triangle or Ceramic interior finishes​

It's also catalytic which should make it a cleaner burning insert.

I asked them if there is anything behind the steel panels to obtain that insulation, their answer is that behind the steel there is vermiculite, and that the difference between steel+vermiculite and Skamol is negligible! That sounds good. You can easily exchange the steel panels for Skamol later, if you like.

 

[begreen]

I like the steel interior protecting the insulation. The interior of the firebox will get occasional bangs from adding splits, especially to a hot stove.

 

[rickj]

I like the steel interior protecting the insulation. The interior of the firebox will get occasional bangs from adding splits, especially to a hot stove.

Exactly my idea, I like that too. Here in Spain much of the wood you buy locally is very hard chunks of olive, and unsplittable (by me), and when they fall over… The 20 mm steel bottom plate won’t be backed by vermiculite, but I could always put a plate of vermiculite on the bottom to see if it makes a difference. (Thanks for stressing also the metal version is insulated.)