OK, so you want to get better control over your fermentation temps, since it's the middle of winter and your basement is getting down to 50 degrees overnight, but you don't want to spend lots of money on a brew belt, fermwrap, or "Son-of-fermentation"-style chamber with heater. Maybe wrapping up your fermentor in an electric blanket or sticking it in a closet with a space heater has helped, but you've come back to find that your temps have drifted well out of optimal range, and you want some way of controlling that heat.
Luckily, you can probably build a decent heater right now, if you're willing to scrounge around and deal with a slightly heightened level of personal risk!
Cardboard box, big enough to hold your fermentor plus some space. This should be free; if you don't already have this, steal it from work or fight a hobo for one.
A home thermostat. Remember when you upgraded yours so that you could program it, or gain a digital display, or run that new heat pump? And you couldn't bear to throw away the old one, since it was still perfectly functional? Guess what, you just gained yourself a temperature controller! I've actually got TWO sitting in my basement. Don't ask.
Anyway, you'll want to set it to "heat", turn fan to "auto", configure it for electric heat, and verify which contacts get switched. Might
be a good time to make sure that it can handle 120 AC...many of them can't...in fact, mine is rated for 24 VAC, 1.5 A, but the relay within it can take 250 VAC, 2 A, and the way I have it wired bypasses any sensitive traces. If you aren't sure, be sure to take LOTS of pictures and post live updates for our amusement.
A standard power cord and 40-60W incandescent bulb with socket. Check your cupboard where you kept all the old bulbs that you switched to CFLs, and your basement where that old Pentium II that you can't give away is tucked in the corner.
Now hook it up! Cut the female end off the power cord and strip the wires. White goes to the light socket, black goes to the thermostat, and another wire runs from the thermostat to the other side of the socket. Duct tape the thermostat securely to the top of your fermentor.
"What about that green wire?"
I'm glad you asked. That green wire is for PUSSIES. Don't use it.
Now put the light bulb in something heatproof to space it a bit away from the fermentor and the cardboard box. Turn the thermostat down below the ambient temperature, plug it in, and check for leaks.* Now turn the thermostat up and watch the bulb come on!
Now place something opaque between the glass and the fermentor, set the thermostat to your desired temperature, drop the box over it, and you're done. That object in the front is ONLY there to give you a sense of scale, I swear.
You can cut a small hole in the top and slide a glass thermometer in to keep an eye on the temperature. You can also set the whole assembly under a smoke detector if you're the kind who likes to know when your temps exceed your setpoint.
There you go! Free ferm chamber. It was fun building this, although I have to admit that I hope the supplies to build my real
ferm chamber arrive soon!
I accept no responsibility for any damages that you or your beer might suffer if you actually build this. It works--I'm using it right now--but it's hella ghetto. The key safety parameters are making SURE that your thermostat can take 60W @ 120VAC, making SURE your wiring is solid, and making SURE your light bulb isn't getting too close to anything flammable or even meltable. But hey, if little girls across the country can operate an Easy Bake oven without incident, there is no reason why this can't be safe, right?
*An electricity leak can be identified by a popping or buzzing sound, a flash of light, and/or some acrid smoke. Is your home/renters insurance paid up?