Home | Parts List | Cut List | How-To
The easiest, most standard parts list is below, for a single run to a local big-box hardware store. See the sections below for online alternatives or upgrades. Links are so you can see a sample of what the piece looks like, you can substitute whatever your local store has available.
I built mine for $36, but sourced a few parts from Amazon and wired in a cheaper lamp holder and dimmer, YMMV.
Insulated Foam Board $17 per 4'x8'board, $5.56/med box
Polyisocyanurate Foil Lined Foam Board 4' x 8' x 1". (Thicker foam can be used, 1" is what is at my local big-box stores. Note if thicker board is used, interior dimensions each way are reduced by 2x the thickness difference)
Cannot be bought in smaller sizes that I've seen. Can make 2, 3, or 4 boxes per sheet.
Non-foil lined (Foamular or XPS foam) should work as well, though I haven't tested the foil tape on it. The foam I have linked also has a higher flashpoint.
Foil Tape $7.36/roll, $2.45/med box
Foil HVAC Tape (do not use standard duct tape) At least 1.83" wide; wider is easier (2.83" linked)
You need about 16 yards for a medium box. The linked tape is 50 yards, enough to build 3 medium boxes.
Weather Stripping, $2.88
Foam Weatherstripping 3/8" max width. Thicker (more cushion, not wider) is better if you have it. Two lines of weather stripping (one on lid, one on box) offset is required.
14 linear feet for medium box, or 1 17' package, linked.
Foam weather stripping gets a bit sticky, making the box (slightly) harder to open. Get rubber if you can, but make sure it's 3/8 inch wide or less.
Fan - $14.57
4" Duct Fan (if someone can find a cheaper version that can withstand 180F or so, please let me know!)
Any fan should work; I have had little luck finding which fans can operate in the 160-180 range; perhaps just a $5 desk fan from Target would be fine?
Someone told me their local big-box doesn't carry this, and had to order it from Amazon. FYI!
Dimmer Switch
Plug-n-play Dimmer $13.28 (Cheaper option that requires wiring in "Cheaper alts" section below)
May be optional if your heatsource happens to reach steady-state in the acceptable range. A 40W bulb did for me
Thermometer (Varies widely in price, $3-20. If you have a meat thermometer just use that)
A Meat Thermometer like this works well, just stab it through the side. A digital thermometer with probe works well too.
I used four thermometers for testing; a more expensive one with probe I already owned, an Inkbird ITC-1000 Thermostat, a meat thermometer, and one of these. This turned out to be overkill as they all worked well and agreed.
Heat Source - Fixture
Clamp Lamp Holder $6.46 or Box Lamp Holder $1.73.
The clamp light is easier, requires NO wiring, but is about $5 more.
If you get the Box Lamp you need to know how to wire it to a plug, and properly insulate it: Be VERY careful wiring anything inside of a foil lined box, it is conductive! Everything needs to be heavily wrapped in electrical tape or, better yet, heat-shrink. If this makes you hesitate, just use the clamp fixture!
Heat Source - Bulb
Your wattage needs to be high enough for the air volume you're heating, at the ambient temperature outside the box, and the interior surface area of the box. If we do the math, in an ideal world, we find we need 29.8 watts, 40.4 watts, and 71.7 watts, respectively for the small, medium, and large boxes to just maintain the temperature at 100F difference between inside and outside. Since we're not in an ideal world, we need to buy somewhat larger bulbs even with the fan running at 15 watts.
Buy:
A 40 watt bulb minimum for a small box for $1
A 60 watt bulb minimum for a medium box for $2.50 (One pack available, not the six linked)
(I tested a 40W bulb in my medium box and it exactly held 160F. This may work for you, and you could forgo the dimmer, but if your box is even slightly more leaky a 40w will be too small, and you'll need a 60W with a dimmer)
A 100 watt bulb minimum for a large box for $2.50 (Might as well bump up to the linked 125W heat lamp bulb at this point)
Measuring Tool - Tape measure, yardstick, fabric tape. Drywall Square would be absolute best/fastest, but not required.
Marking Tool - Sharpie preferred
Cutting Tool - Utility knife or Exacto knife works well. Steak knife also works fairly well. Unserrated preferred. A snap-off utility blade like this is ideal for extra length to finish the foam cut.
Straight Edge - You need a straight edge. Longer is better. 1' is probably the minimum, up to 4'.
Coming Soon!
Let me know if you find a cheaper source; send me the link and I'll put it up. No affiliate links, please!
Alternative Heat Source
Ceramic Heat Bulbs Should be able to handle very extended run-times in warmer environments safely. Not available locally, and in fewer wattage choices, but would be a nice Amazon upgrade.
The obvious upgrade for this is a PID controller. This will keep your box at a consistent temperature without cycling, by acting as a thermostat and cycling your heat source on and off. Further, you can use a larger heatsource (AKA higher wattage lightbulb) since you don't have to match the heatloss out of the box to the wattage in, so you can bring your box to heat much faster.
When time allows, I will be posting a how-to include a Inkbird ITC-1000 Thermostat in this design.