I recently installed a small gas fireplace. It's a great unit but it doesn't circulate heat very well without a fan. I wanted to improve the heat output and found this fireplace fan on the web. While the fan looked very professional, the price ($140) put me off. So I decided to build my own.

Materials:

Computer fans (2), $2.99 each, Newegg.com
Fan noise dampeners, $1.99 for a pack of two, Newegg.com
AC adapter / power supply, input 120V AC, output 12V 500ma, Model TEAD-41-120500U, $2.99, eBay.com
Panel-mount stereo 3/32" submini phone jack, $2.99, Radioshack.com
Steel sheet, 26 gauge, 12"*12". You can find this near the roofing and sheathing materials at Home Depot but basically any sheet that you can cut will work.

Tools:

Dremel
Soldering iron
Work bench
Drill and a drillbit slightly larger than the threaded part of the phone jack
Ruler and pen

Step 1: Mark Fan Screw Positions

Using the dampeners as a template, mark the position of the fan screws on the steel sheet. Leave about 1/4" inch between. Drill the holes. This will give you two squares.

Step 2: Draw Circles

Find a round object such as a mug that has the same diameter as the fan blades. Use it to draw circles in the middle of the squares.

Step 3: Cut Fan Holes

Install a metal cutting disc in your Dremel tool. Cut along the circles. Do this step outside as metal dust and sparks will fly everywhere. Wear gloves and eye and ear protection! The cut edges will be sharp. Use a sanding stone to finish them and round any other sharp corners.

At this point you can also cut the metal sheet to the correct width. It only needs to be as wide as the two fans.

Step 4: Measure and Mark Bend Lines

Draw a line at the bottom of the squares, below the fan holes. Measure one fan thickness (25 mm) from the first line and draw a second line. Measure one fan height (80 mm) from the second line and draw a third line. Cut the sheet to the right height along the third line (leftmost in the picture).

Step 5: Bend Sheet 45 Degrees

Secure the sheet into a workbench at the first line and bend it to 45 degree angle.

Step 6: Bend Sheet 90 Degrees

Then at the second line and bend it to 90 degree angle.

Step 7: Attach Fans to Case

Attach the fans into the case. Order of compilation from the front:

screw
plastic grommet
blade shield
case
noise dampener
fan
rubber grommet
nut

The grommets are optional but help reduce vibration and noise.

Step 8: Solder Wires

Twist the positive (red) wires from each fan together and solder them into the positive leg of the phone jack. Twist the negative (black) wires from each fan together and solder them into the negative leg of the phone jack.

Step 9: Mount Phone Jack

Drill a hole somewhere on the case to mount the phone jack. Push the jack through and secure with the nut provided. Stash the cords inside the case so they don't come into contact with the spinning fans.