Aquatic Plants Digest V1 #22

>I finally broke down and decided to try DIY substrate heating.  My
>basic plan is that of Dan Resler and Uwe Behle, but I want to build
>mine out of locally available materials.  I am going to build a 30W
>heater for my 70 gallon tank (footprint 48" x 18").
>I've decided on a 24V, 2A transformer, and 30 gauge wire-wrapping
>wire, both from Radio Shack.  The only major problem is that I need
>200 feet of wire to get 30 watts of power.  I'm going to do this using
>4 reels of 50-foot wire, wound in parallel on a frame built of solid
>steel-core, vinyl-insulated clothesline from my local hardware store.
>The ends of the reels will them be soldered together to connect the
>four reels in series.  The frame will be glued to a 46" x 16" piece of
>plastic carpet backing and placed at the bottom of my tank.  Add
>gravel, and I should be all set.
>The only tools I'll need should be a drill , soldering iron,
>screwdrivers, and cutting pliers, all things I already have.  
>I expect the total cost of the installed heater to be under $50.
>Any suggestions/comments?
>- -Shaji

You can simplify your project by using a 12 volt transformer instead of
a 24 volt one if you are using 30 guage wire.  You only need about 10
meters of wire at 12 volts. Here is a repost of an article I posted
about the one I built:

I have a 70 gallon tank,  and I decided to go with a low power heater that
I could leave on all the time,  a la Dennerle.  I used 10 meters of 30 gauge 
wire (the kind used for wire wrap).  I used an undergravel filter to hold the
wires in place by drilling holes in the sides and threading the wire back 
and forth through them.  I soldered the ends of the 30 gauge wires to 18 
gauge wire and covered each solder joint with heat shrink tubing (because of
the difference in the size of the wires you need  to use several sizes of heat
shrink,  and use it build up the diameter of the 30 gauge wire).  The other 
end of the 18 gauge wire I attached to  the + and - terminals of a 12 volt 
switching power supply ($22 at a surplus electronics store).  The switcher is 
as efficient as a transformer,  costs about the same,  and was easier to find.

Technical details:
  10 meters of 30 gauge = 3.45 ohms
  Since P = V^2/R,  P = about 40 watts.
  This means you need a power supply that can supply 3.33 amps at 12v,  
  or 4 amps to be conservative.