I need advice?

[ceresone]

I'm building all raised beds. One of my beds, I want to use for a "hot" bed. It is 16'x4', The back side, to the North is 4 -7 1/2boards high, making the back 30' " high, the front is 22 !/2" high, ends will have a slant to them. I have storm windows following the slant, on south side.
I would like to use it to start seeds in the spring. It can get to 10 degrees here at night.
My question--do I need to insulate? need heat? I know what I want for end results-but getting there is what I dont know. Help?

[dice]

There are two basic ways, heating it with manure in a 2-3' deep
hole with a thin layer of topsoil on top or heating it with buried
electric heating cables. Some people pile straw bales around
them for insulation on the sides.

Some examples:
http://www.holon.se/garden/howto/hotbed_en.shtml
http://www.energybulletin.net/node/46012
http://www.backwoodshome.com/articles2/martin104.html

A link from a university (that seemed a little too general in
its information, hence I have not included it) mentioned that
for an electrically heated hotbed, you need about 2' of heating
cable for every 2 square feet of hotbed. (Basically you
sandwich the cable between layers of hardware cloth and sand
to keep critters from chewing on it and to allow drainage around
it, about 6-8" down below the top of the soil. It should have a
thermostat.)

Edit:

Make that 2' of heating cable for every square foot of hotbed.
So for your 4'x16' bed, you would need 128' of heating cable.

Here is that link that I omitted. Skip down to "Electrically-Heated
Hotbed" if you just want to see the description of how to do that
part:
http://www.ianrpubs.unl.edu/epublic/...licationId=791

Figure that your wiring out to the hotbed probably has to be up to
electrical building codes (probably a 18" deep trench with wire inside
conduit, a ★★★★★★★★ box for it on the side of a building with a gfci breaker
in it, etc).

Also, several of the links mention covering the top at night with
extra insulation. With a 4' x 16' bed covered by storm windows, you could
use two 4'x 8' sheets of compressed foam insulation with straps of couple
inch wide velcro glued to them in a couple of places on the long sides and
on the corresponding sides of the hotbed (to keep them in place in the
wind). If you have room around the hotbed, and while still using them,
you can just unhook the low side and flip them up and over to let in the
sunlight during the daytime. Once you are done with them for the season,
you can unhook both sides and store the covers someplace out of the
way. That avoids messing around with blankets, quilts, and anything
that soaks up rain for your night time insulation on top of the hotbed.