pit insulation question

Posted: Wed Oct 19, 2011 4:50 pm

what is the best insulation for my fire box? can i use wool carpet padding to lay over my pit to help hold in the heat? thx

Posted: Sun Oct 23, 2011 4:31 pm

Thermal Insulation
About Selecting Thermal Insulation

Temperature Resistance

Many types of thermal insulation are designed to perform in a variety of temperature ranges. For insulation that resists cold temperatures, see Rigid Polyurethane Foam, PVC Foam, and Cork on page 3483and Polyimide Foam on page 3486. For insulation that resists high temperatures, see Fiberglass and Mineral Wool on pages 3488-3490. For insulation that resists ultra-high temperatures, see Ceramic, Silica, Calcium Silicate, and Millboard on pages 3492-3493.

Heat Flow Rate

Also called the K-factor, heat flow rate measures the rate of heat flow from one side of the insulation to the other. The lower the heat flow rate, the slower the heat will flow through the insulation and the better the material will insulate.
Another term related to heat flow rate is R-value, which measures an insulation's capacity to slow heat flow (see tables below). The higher the R-value, the better a material insulates. R-value is equal to the thickness of a material divided by its heat flow rate (K-factor). For example, a 1/2" thick piece of insulation with a 0.25 heat flow rate has an R-value of 2 ( 1/2"/0.25) while a 1" thick piece of the same material has an R-value of 4 (1"/0.25).

Protecting Insulation and Improving Its Performance

Some insulation comes with or may be used with a jacket or facing that protects it from outer surface conditions such as water, weather, and abrasion. A coating of latex paint ( 4530K183 ) or PVC jacketing (see page 3490) makes many suitable for outdoor use while metal jacketing (see page 3491) is an even stronger alternative. Because the jacketing and facings come in contact with the insulation—not the surface being insulated—they may not require as broad a temperature range.

Insulation
Material
Pages
R-value @ 1/2" Thick
R-value @ 1" Thick
Expanding Foam 3482 2.5-3.0 5-6
PVC Foam 3483 2.6-3.0 5.2-6.0
Polystyrene Foam 3483 1.9-2.5 3.8-5.0
Polyurethane Foam 3483 1.7-2.6 3.3-5.3
Bubble Wrap 3482 2.1 4.2
Polyimide Foam 3486 2.1 4.2
Polyethylene Foam 3484 1.9-2.0 3.8-4.0
Mineral Wool 3490 1.9-2.2 3.7-4.3
Foam Rubber 3485-3486 1.9 3.7-3.8
Insulation
Material
Pages
R-value @ 1/2" Thick
R-value @ 1" Thick
Melamine Foam 3486-3487 1.9 3.8
Cork 3483 1.8 3.6
Cellular Glass 3487 1.7 3.4
Fiberglass 3488-3489 0.8-2.4 1.7-4.8
Silicone Foam 3486 1.3 2.5-2.6
Ceramic 3492 0.4-1.8 0.8-3.6
Silica 3493 0.6 1.3
Millboard 3493 0.5-0.7 1.0-1.4
Calcium Silicate 3493 0.5-0.7 1.0-1.4

Posted: Sun Oct 23, 2011 4:35 pm

Page 3482
http://www.mcmaster.com/#thermal-insulation/=emcatk

Posted: Mon Oct 24, 2011 6:02 pm

Buy a welders blanket,fire proof.

Posted: Tue Nov 01, 2011 9:16 am

Are you making insulated barrels ? Need a flexibile material, it is available, but its different than the rigid board stuff.

When I was researching insulation, I saw there was some foil backed mineral wool products. The next cooker I build will have a layer of aluminum facing the the metal surface to reflect the infrared heat energy back into the pit. That would be for the cook chamber for sure, but you would need to check the specs for something that would reflect the heat and still hold up to extended periods of high heat over 1000 F just above the grate.

If you are using a stoker fan, the charcoal fire can get hot enough to make metal glow (850F or more easily) and I have measured spikes over 1,000 degrees in my heat transfer tube that is several inches away from the grate. There is an awful lot of heat in the firebox area, so fireproof and reflective material like the suggestions above would be good choices.

My current firebox is still naked - I have it enclosed on the trailer to keep wandering hands away.

Posted: Sun Nov 20, 2011 3:30 pm

I have always used roxul it has a highheat piont of 1800-2100 i think