Advice please on insulating a file cabinet smoker

[Vic.]

Hi all, I'm just in the process of building a gas fired smoker out of a file cabinet and I'm in two minds in how to insulate it, on the inside or the outside. Would it be best to heat up the file cabinet and insulate it with a thermal blanket on the outside or insulate the inside of the file cabinet, thus saving energy in heating the steel.

As I don't intend on having my hot smoker above 220 degrees F, I was thinking a product called ThermaWrap (which is a fire retardant foil) could line the inside. There's no glass fibre filling, so I was wondering if you think it would be OK to use inside my smoker or would the over blanket be the best route? There's also water repellent foil tape available so I can make the inside a good seal.

The ThermaWrap product I was looking at has these properties:

Equivalent to 100mm of Glass Wool
CFC & HCFC Free
Thickness 15mm approx.
Non toxic, non irritant
Completely 100% recyclable
1.393M2K/W
Class 1 surface spread of flame tested to BS 476 Part 7

http://www.thermawrap.co.uk/index.html

[British BBQ Society]

I am afraid I dont know the full answer but I would suggest insulating on the outside unless you are filing a cavity like the FEC's where they have stainless steel inside and out. If you are considering inside (which I wouldn’t) try to find out exactly whats in the insulation, I wouldnt want any food contaminated.
Cheers
Toby

[Steve]

Toby's bang on there. You need to put the insulation on the outside unless its certified food safe.

Also you'll need to strip any paint from the inside of the filing cabinet, might be easiest if you get it shot blasted. From experience of stripping the insides of oil drums I can tell you it's a nightmate getting into the corners.

If the foil you are looking at is the stuff with air bubbles in as well, they will burst. I tried that stuff as an insulating jacket on a ProQ and most of the bubbles popped leaving tiny bits of foil stuck to my cooker. I was running my cooker at 225F during a test run when I did this.

I can't say much more than this, hopefully someone else will chime in with some more info.

[Vic.]

Thanks for the advice.

Steve, you've pretty much saved me alot of hasstle about not using a foil bubble wrap . If I shot blast the inside how would I protect it from rusting?, might look around for thermal non-toxic paint to put on the inside.

Do you think the Thermawrap quilt would be an ideal outer covering? I can cut it and seal it to size with the foil tape. Make we flaps for the drawers etc

http://www.thermawrap.co.uk/superquilt2.html#

Product Description

19 Components
Thickness 40mm approx
Weight = 800g/m2

Mechanical Properties

Thermal Performance = 2.71m2K/W (roof), 2.44m2K/W (walls), 1.38m2K/W core resistance (floors)
Flammability = Class 1 surface spread of flame
Water vapour resistance = 1569MNs/g
Emission coefficients of surfaces = 0.05
Tensile strength = 142KPA

[Steve]

Once you've shot blasted the inside, wipe it down with cooking oil, then run the cooker a little hotter, say 250F for a while and the oil will adhere to the inside. You're seasoning it, like you do with a carbon steel wok or cast iron pan.

The quilt stuff looks like it might be ok, having not seen it in person though I couldn't be sure.

[Vic.]

Thanks again. I seem to have everything sorted, now its down to the hard work, LOL. Lots of good info on this site, found out about using VHT paint on the outside of the smoker too would be ideal to use along with the blanket

[Steve]

Please post pics of your build, there's not many gassers on here but it wil be interesting to see what you're doing.

[Vic.]

How can I tell if its galvanised steel? if it rusts do I know its not galvanised? here's a pic of it. sheet Steel is 1.5mm thick.

[Vic.]

Also if you are going with gas then run the numbers for gas to air ratios . You do not want to starve it for air only to open the door and it toast you with a nasty flash back.

I have a friend who works with gas, I'll get him involved to sort out the connections, airflow etc. Thanks

[Vic.]

Rub come of the paint off and let it sit it it starts to rust then it's not coated.

The whole thing including the drawers, bearings, etc is galvanised. It's only on the surface as some areas OI rubbed with wire wool are rusting, its all gonna need sandblasting though

How are you going to seal up those drawers? Are you removing them and rep;acing with one large door?

What do yous think on this?

After considering my options and realising second-hand solid tool boxes are like hens teeth around here, I'm gonna rip out the drawers and weld an air tight steel box to fit inside my filecabinet, along with a big solid door with something like fiberglass tadpole seal around it. no need now for the filecabinet to be sandblasted and the gap between the inner box and filecabinet will provide good insulation and disperse the heat evenly.

anything else I need to know in advance before getting this box made and installed? will an air gap be sufficient or should I pack it something?