Building an insulated fermenting box?

I live in New Zealand and around this time of year the temperature averages around 10-15 degrees.
I was thinking about making a wooden box to store my brew out of some basic materials from the local hardware store.


Let's say I make a plywood box large enough to keep a 25l plastic brewing barrel and my bottled beer during secondary fermentation.
If I use polystyrene walls for the interior of this box, in theory, this should keep the heat at a constant.
I will varnish the plywood to stop any water damage (The box will be outdoors) and, once assembled, fill the gaps of the box with a silicone sealant.

If my brew is at the right temp. when I place it in the box would I be right in assuming that it should be good for the primary fermentation process? Or will I need some sort of heating (Not too keen on this, really I just want something that wont use any electricity) but if needed should I use something along the lines of a light bulb attached to a thermostat controller?


Does this sound like it will work to anyone with experience? If not where have I gone wrong?

This was a really ghetto box that I did, but hey the box was on sale for $20 at home depot. It was a vanity for a bathroom sink, and I sealed it up with foam insulation board and made a top for it. I keep it inside so I haven't really tested it, but I keep it inside and can change the temp and keep it fairly constant every few days with a refresh (2 L bottle either frozen or hot water depending on the need).

I was recently looking at bathroom vanities to make something very similar for indoor use. Need to figure out how to set up two chambers, like the son of fermentation chiller, so I can do the temperative-controlled ice-driven cooling and a ceramic heater for heating.

Looks good, does anyone know how I could incorporate a lightbulb without losing any insulation because of the power supply (Maybe a cord going through the polystyrene hooked up via an extension cord or if possible hooked up to a car battery charged via solar panel or something similar in a separated uninsulated section of the box?)

A few options:

To run any wires into it, just drill a hole, run the wire, and silicone it up.

The heat alone of your fermentation might be enough...you'd need to run a test fermentation to know for sure. In fact, it might be too much! In this case, you could make kind of a reverse "son of a fermentation chamber", and have a fan to exhaust hot air and pull in cool air, (run the fan off of the temp controller).

If you are sure that it's always going to be too cold, I'd build a chamber with a heat source and a fan, and a dual temp controller, (I love the ebay one...$30 and it can do both heating and cooling). Hook the fan up to the cooling circuit, and the heat source up to the heating circuit. Then you are sure to stick within your range.

Also, light bulbs are iffy....they produce lots of heat, but they also put out light that you have to shield your beer from, (that much light, that close, could skunk the hops...incandescents still put out a BIT of UV, (though very little....it' PROBABLY isn't a concern)). Still, if it were me, I'd use a heating pad, (like what you use when you have a sore back), instead of a light bulb.

Ceramic terrarium heaters screw into light bulb sockets and don't produce any light.