DIY fireplace fan

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 a fireplace fan on the web. While the fan looked very professional, the price ($140) put me off. So I decided to build my own.

Update: This project was featured as Editor's Choice at Instructables.com!

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, 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
  • Screwdriver
  • Ruler and pen
Steps to build:
  1. 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.

  2. 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.

  3. 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.
  4. At this point you can cut the metal sheet to the correct width. It only needs to be as wide as the two fans.
  5. Measure one fan thickness (25 mm) from the bottom of the squares down and draw a line.

  6. Measure one fan height (80 mm) from the first line and draw a second line.

  7. Cut the sheet to the right height along the second line.
  8. Secure the sheet into a workbench at the first line and bend it to 45° angle.
  9. Then at the second line and bend it to 90° angle.
  10. Attach the fans into to 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.

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

  13. 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.

  14. Glue furniture pads to the bottom of the case to eliminate vibration and noise further.
  15. Plug it in and test.

  16. Position the fan near the back of the fireplace and plug it in.

Possible further enhancements:
  • Adjustable fans. They come with a potentiometer that allows you to adjust the speed. The higher the speed, the noisier the fans so slowing them down makes sense.
  • Fans with a temperature sensor. A sensor linked to the fan's motor automatically controls the speed, adjusting it up as the ambient temperature around the fireplace rises.