This is how we're going to accomplish this feat. We are going to move the temperature control out of the heater's case and into a wall or project box. It's quick, simple, and will have your room staying at a much better, more even temp through the cold months. I would like to apologize for not having any pictures on this one. Apparently I have misplaced my camera and it may take me some months before I can find it again.
Step 1: The Things We Need for This...
An old heater that uses the same or more wattage than the one we're going to be controlling.
A deep outlet box
A 20 amp wall socket
A cover plate for the wall socket
Optionally, you may want a 20 amp light switch, a larger wall box, and a cover plate that has holes for a switch and outlets. (this being the kill-switch option)
A Dremel (Highly recommended but not necessary)
An electric drill (battery or corded)
A soldering iron and solder (may or may not be needed depending on the heater you get)
A crimp tool
A pair of needle nose pliers
Screwdrivers of the appropriate size and type
A hobby and/or utility knife
Step 2: First We Disassemble the Old Heater...
In some cases this can be quite difficult as they use weird screws on us like tri-wing or security torx. That's OK because your never going to use this again anyway right? We unscrew them if we can. Note that you can buy a cheep screwdriver for about a dollar at most thrift stores. It's easy enough to mod one of those into a workable driver with a Dremel. If not we take the Dremel or what ever means you deem necessary to it and cut open the case. Even a hacksaw would work for this. Make sure to stay away from the area where the cord goes in and the thermostat. Those are the parts we want to keep.
Once you have the case in 2 pieces we can start to disconnect the wires. In some cases they are welded on instead of having wire nuts or slide disconnect lugs. This is not a problem. If you can't just disconnect them simply cut the wire as close to the connection as you can. We can easily fix that problem later.
To get the cord out, take a pair of needle nose pliers and squeeze the cord strain relief from the inside of the case and push it through. If yours has a strain relief that's mounted with screws on the case just take those out and free the cord. Some heaters with plastic cases simply have built in strain reliefs in which case you just take the knot out of remove the cord from the loop-around and slide it out of the case.
To remove the control mechanism we first have to remove the knob. Most of them slide off and some have a set screw near the base. For those that slide off you should be able to just grasp the knob firmly and pull. Some may require a bit of lateral force with a screwdriver or other thin pry-bar of some sort. Those with a set screw will need to have that loosened before they can be removed. To do that just figure out what kind of screw it is and get the appropriate driver. Most are either Allen key/hex drive or American standard Flathead. Just use the old adage "righty tighty, lefty loosy" for this which refers to the top of the tool as you look at it. If you move the top of the tool towards the right, the screw/bolt/nut get's tighter in most cases. The opposite is true for left ergo the saying.
Once you have the knob off, most of them will have a collar nut around the shaft of the temp control. For this you can use a socket wrench, a crescent wrench, or even a pair of regular pliers.. As long as you can get it off without damaging it much it's fine. Remember, we have to reuse this later. After you get that off the temp control should slide easily through the hole it's mounted in. If not check to see if it's still connected inside the case somehow. Now is a good time to test it to see if it still works as this may be the part of the heater that failed. This can be done with a multimeter that has a resistance checking or continuity test feature.
I know this can be frustrating. Just try not to go ape on it and beat it with a hammer or something...
Step 3: OK, Let's Start Building...
For the wall box we will first need to drill a hole near the bottom. Make sure you don't make it to close or your going to have a heck of a time getting the temp control into it. That means it's time to measure. This doesn't need to be terribly exact. We just eyeball where the center should be, put the temp control device on the outside of the box about a quarter of an inch from the bottom. Seeing where the shaft is located on the device should give us some idea of where and how to reposition it if we need to. Mark the spot where the shaft needs to be on the box with an awl or just drill a small pilot hole with the Dremel.
Now we need our drill. Dremels are nice but they don't handle big bits like we should use here. The point is to remove most of the material that we need to cut away to mount the control device. You can use the Dremel with a carving bit or it's router attachment but it takes much longer. You'll want a drill bit that is just a bit smaller than the shaft we need to mount. An easy way to gauge that is to take a piece of paper and cut a notch in it that matches the size of the mounting shaft. Then, match it up to your drill bits and pic one that's just a bit smaller. about one 64th of an inch less will work though it's OK to have a 16th or so. Now we drill where we marked with the big drill bit. That takes most of the excess material out of our way. Now we can use a high speed cutter or a sanding wheel to remove the last little bit. Be sure to check the fit of the mount shaft frequently and get the best fit you can, the tighter the better. A tight fit will insure that the control won't move once it's mounted.
We mount the cord simply by slipping it through the tab at the bottom of the wall box and tie an underwriter's knot. You can find out how to do this at About.com. Be sure to leave enough length to connect it to the outlet and the controller (and the optional switch if you chose to add that).
Step 4: Now Let's Make Our Connections...
Here are your color code instructions:
Green is ground, Black is hot, and white is neutral. To further explain this, the ground wire goes, well, to the ground. It's there to catch any large spikes of power that may jump to other parts of the device causing you to get shocked or even a fire. It's important so don't clip those ground lugs off of your cords to make it fit in something it wasn't intended to. Buy an adapter if you need to do so. Their cheep, like $1.50 or so. You could easily collect enough pop cans to make that much so no excuses...
Black being the hot wire is the main transmission wire. If you didn't know this already, your power is a radio transmission that comes from the power plant. It broadcasts at 60hz and about 5000 kilowatts for small residential areas and more like 100,000 kilowatts for cities like New York or LA. Which brings us to the white wire or the neutral. It acts as a middle man. In the peak of the wavelength it's the negative side and in the trough it's the positive. In other words neutral...
The black wire is the one we want to pay the most attention to as it's the most likely to shock us. Now you shouldn't be working on this while it's plugged in so if you are, unplug it now please. I don't want to hear about your hospital trip because you got zapped. And if your prospective other smacks you around because you blew the circuit breaker, that's not my fault either.
The black wire goes to controller and then the brass screw on the outlet. It's the wire that should be switched because it is the one that has the highest potential of shocking you. The temp control device is nothing more than a switch. It turns on when it get's cold enough and off when it's warm enough. If you added the light switch you would first connect the black wire to the switches "common" terminal. Then you attach a heavy gauge wire to the terminal that's labeled "N.O." which means normally open. and attach the other end to the controller. Then attach another short piece of wire to the other terminal of the controller to the brass screw on the outlet. These are sometimes also anodized black. The white wire goes strait to one of the silver screws on the outlet.
Now we're left to deal with the ground wire. This is particularly important because this is what keeps you from getting majorly shocked in the event of a lightning strike. If you don't attach this properly your asking for trouble. To connect it, we need our crimp connectors and our crimp tool. Start by taking out a large ring lug, one that is big enough to go over the mounting shaft of the controller like a washer would. Next get a short piece of wire (12ga or better) about 6 inches long and strip about a quarter inch of the insulation off from both ends. Now crimp the large ring lug on one end and a spade lug on the other. attach the other end to the green screw of the outlet. If your cord doesn't already have one on the green wire crimp on a spade lug there too and attach it to the green screw of the outlet. If you added the kill-switch make another piece the same size with spade lugs on both ends. Attach one end to the green screw on the switch and the other to the green screw on the outlet.
Step 5: Now Let's Mount Everything...
OK, lets mount the outlet (and switch if added). The first thing we need to do is compress the wires into the cavity of the box. The thing we want to be careful with here is that we don't crowd the controller's moving parts. If we do that it won't be accurate anymore and that's bad. Once you have those stowed neatly in the box then we screw the outlet (and switch) into the box. Now let's take a second here and see if doing this has crowded the controller. If it has take a screwdriver and scoot the wires to the other side of the box. Another option is to make a small panel out of Masonite or a thick plastic to go between the controller and the wire mass. You could even cut the piece from the old heater's case for that matter. If it's metal then you need to make sure it doesn't contact any of the electrical connections as this would cause them to short out. That's not a good way to keep the peace in marital situations. They don't like having to take us to the hospital or put out fires. Just trust me on that one.
All we have left now is the cover plate and testing. Since I'm pretty sure you can figure out how to attach the cover plate let's move on. To test this thing we're going to use a table lamp or other visible means to see if it works. Even a night lite would work fine. We just need something we can plug into it to confirm that it connects when we "turn up the heat." I've found that visual things are better here especially if they don't draw near as much wattage. All you need to do is plug it in and turn up the knob until the light clicks on. If the light turns on but flickers we're going to need a better controller. A faulty connection like that can get very hot in a short time. Especially if it spot welds itself shut. That's why the lamp instead of a full on heater.