Both sides made valid arguments, but I needed to cover my radiators to protect my children. I decided to incorporate all of the best ideas I had found and a few of my own into one design.
Step 1: Efficiency and Insulation
Some people say you are preventing a radiator from transmitting heat to the air and surrounding area when you cover it. Other people say that because the hot air coming off the radiator goes straight up, a bare radiator is an ineffective way to heat your house.
Radiators do circulate some hot air around the room, but the majority of the heat is transmitted via radiation. Because most radiators are on the outside walls of a house, a lot of the energy is wasted warming an exterior wall. Many sites suggest insulating the backside of the radiator with a foil insulation to reflect the radiant heat back into the room. This is a smart thing to do even if you are not going to cover your radiators. If you plan to use your radiator cover as a shelf, some people suggest lining the underside of the cover's top with this insulation to keep it cool.
Radiator cover efficiency
Benefits of covers
There are many different types of foil insulation, but ideally you just want something with a foil coating and a thin insulation backing. I actually got my insulation at Lowes, but I really like the selection at insulation4less.com
Excellent selection of insulation types
Foil bubble Insulation
Step 2: Covered Vs. Uncovered
Step 3: Selecting a Style
I liked the Mission style best because it still looks like a radiator and it allows air and radiant heat to flow freely out of the slats. I also liked the idea of a vent at the very top of the hollow so that no heat would get trapped inside the case. I wanted to have a design that encouraged convection currents and possibly directed them out into the room where the heat was needed.
I used these sites for ideas:
Wolf Radiator enclosures
Step 4: Design
I used this white wood because it was the cheapest wood available. I didn't care about the knots because I planned to paint it white to match the woodwork in the room. All of the wood used totaled around $40, but the foil bubble insulation cost another $20.
Update: I found a great article on About.com with information about what they call SPF (Spruce, White Pine, or Douglas Fir) wood that is found at the home centers.
The only wood that was not white wood was the top and the plywood back. I bought a higher quality, 4' x 1' solid pine panel for the top because I didn't want it to warp or crack. I bought a 4' x 2' sheet of 1/4" plywood for the back.
You will need:
~18' of 1 x 2 whitewood
~11' of 1 x 3 whitewood
~4' of 1 x 4 whitewood
1" x 12" x 4' solid pine panel
4' x 2' sheet of 1/4" plywood
Keep in mind, this is for a 32" wide x 25" tall x 10" deep radiator. You will probably need to modify these measurements to make it fit your radiator and house.
This Old House
Step 5: Rough Cuts & Doweling
I started the assembly with the side pieces because they seemed to be a simpler task than the front piece. I used my cheap doweling jig to make uniform, precise holes in the ends of the slats. The drill stop allowed me to make the holes just a little deeper than half the length of the dowels. This will make sure that I get the desired strength from the joint, and the dowel's length won't be all on one side of the joint.
Step 6: Pocket Holes
I didn't have this jig when I built the original cover, so I relied on other joints and a few pocket holes. The pocket holes I did use were cut by hand and did not come out as I had hoped. They worked, but I don't recommend it, you are better off buying the jig.
Now that I have the jig, it is much easier to make this joint and I recommend using pocket holes for all joints but the slats. They make a really nice tight fit and the fasteners are all well hidden. I am now building another radiator cover using nothing but pocket screws.
The pictures below show how I used the pocket hole jig to secure the rail (horizontal piece) to the stile (vertical piece). Just follow the directions included with the Jig. The positioning of the jig and the required length of the drill bit are determined by the thickness of boards you use.
Each rail should get 2 dowel holes on each end and on the side for the slats. Where the rail meets the stile, you should also use a pocket screw. Once the sides were assembled, I moved onto the front piece using the same method.
Step 7: Rabbet Joint
I ran the back, inside edge of the two sides through the router with a straight cut bit. This created a nice rabbet that I could seat the plywood back into, so it wouldn't show from the sides.
To smooth the edges of the pine top, I used a 1/2" roundover bit to ease 3 of the sides of the panel. I left the back edge unfinished so it will stay flush against the wall.
Step 8: Final Assembly
Clamp the sides to the front and join them with 2 more pocket screws per joint. Next cut the plywood to size, fit it into the rabbet and nail it in place. Now you can secure the top with the routed edge to the rest of the cover. I used finishing nails since I was going to paint it, but you could use a pocket screw if you were planing to stain the wood and didn't want the nails to show.
Step 9: Placement
Step 10: Update...
After a year of use, the heat made the wood shrink and swell. A few gaps opened up so I filled the gaps with painter's caulk. Because it's acrylic caulk, it resists cracking and is more flexible than wood putty or painter's putty.
I also painted the radiator and the inside of the cover black. This way, the radiator doesn't show through the slats and the foil insulation is less noticeable in the back.