What's the best way to insulate this type of WFO...

[ashley1608]

Hi all,
I'm in the process of building an Oildrum based WFO and need some help with the insulation layers.   The oil drum has Storage heater blocks adhered to the outside for thermal mass, but I'm not sure as to the best methods for the later layers.
Do I-

A: Place a 2" layer off ceramic fibre over the top followed by 2" of vermicrete and render over the top
B: Place a 2" layer off ceramic fibre over the top followed by render
C: Place 3" of Vermicrete over the top followed by Render
D: A different method altogether..
E: Run around like a headless chicken and go and by a pizza from Iceland....................

Cheers for the assist

[spinal]

"Best" is subjective... for some best is the cheapest (cob/hay?) while for others it's the most insulating. Keep in mind that there is no such thing as too much insulation.

Hence, of the three options, the most insulating would be the ceramic blanket + the vermicrete.

Depending on your finished look, you could also do loose-fill vermiculite in a cavity. If budget allows, I would do as much ceramic blanket as you can afford, even more than 2"... then vermiculite/vermicrete...

M.

[minesamojito]

Ceramic fibre, then as much vermicrete as you can get, chicken wire through vermicrete and then render....
No need for E:
Cheers
Marcus

[matthewcove]

I'm just thinking about this too for my oven. Does anyone know the thermal conductivity of a good ceramic blanket compared to loose fill perlite or vermiculite? Under the hearth I have 10cm of foamglas which is 0.041 W/(m.K).

Cheers

Matthew

[cannyfradock]

I haven't got a clue on techy details so I would do similar.....2" of thermal blanket covered with chicken wire then at least 3" of vermacrete (vermiculite, cement and water).....then waterproof render.

If you have a problem sourcing the correct thermal blanket, then google "Sheffield Insulation". They have many stores up and down the country (sometimes by other names). Use their store locator on their website to find your nearest store. They do a roll of thermal blanket suited to our needs. I think I paid about £45 for a large roll from them. Don't use normal rockwool as this is only designed to hold back a fire "once"....after that it disintegrates and turns back to powder.

Terry

[spinal]

Thermal conductivity of vermiculite depends on the particle size as it uses air-gaps for insulation:
www.vermiculite.org/pdf_word/Vermiculite_Data.pdf

The ceramic blanket will depend on what product you use.

That said - keep in mind that in vermicrete, the external air gaps between the vermiculite will have been filled with cement, so that will impact the conductivity. Hence, an uncompressed blanket will insulate better. (thermal conductivity of cement pastes for reference : wings.buffalo.edu/eng/mae/cmrl/Cement%20of%20high%20specific%20heat%20and%20high%20thermal%20conductivity.pdf ). Obviously, the vermicrete conductivity will depend on how much cement/vermiculite you use.

HTH,
M.

[matthewcove]

I'm tempted to use just loose fill Perlite over the dome and do away with the ceramic blanket all together I dont think perlite has a problem with the temperatures as they use it in the construction of low conductivity fire bricks. Had a quick look today and the best ceramic blankets seem to have a conductivity of around 0.15 which is only about half to a third as good as loose fill perlite at 400C.

Matthew

[tonyb]

We are in danger of confusing people with the 2 very different designs.

Matthew, loose perlite or vermiculte would be fine but you need to build a 'container' to hold it whereas with blanket and vermicrete you can render the exterior. If you go loose filling, make sure you have plenty covering the top as it will settle over time, you might also think about making the roof such that it is easy to top up.

Ashley, I wouldn't use loose insulation immediately outside the drum just in case corrosion eats a hole in the drum and you finish up with perlite/vermiculite topping on your pizza

[bookemdanno]

Its all a case of using whats available and playing the odds. Vermiculite bound with cement will always underperform loose, but how do you bind it otherwise?
For instance, you'll find better insulators than CFB, but they won't agree with the temperature, or place further demands upon the oven design.

Like Tony says, you'll need a definite controlling layer above the drum if you use loose fill.

[ashley1608]

Thanks Guys for the info. Didn't realise how many variations on a theme there could be for insulation. Based on your info I will probably go for ceramic fibre over the top of the thermal blocks on the drum ( Vitcas have recommended that I Thermal Screed over the top of them to almost make a solid unit)with as much "devils porridge" as I can get (on probably 4 or 5 inches) I would love to go for a housing with loose fill but a bit outside my budget/skill level.