Garden Hotbed with sash

So here is what I ended up with at the end of the day. It doesnt look real pretty, but it should serve it's purpose. I bought two of the sash for five dollars each, some body gave me one, and I had some plexiglass and made one for about $15 . The bundle of foam cost $18. So its more or less a $35 dollar project. The picture doesn't show it very well, but the sash slope away from the shed.  Yesterday was the second day and I put a thermometer in the soil. It said it was 30 degrees, which was a little disappointing. This morning it read 30 again, but it got down to 18 degrees last night. I am covering the sash at night with more sheets of foam. Today was sunny and at 5pm the thermometer read 60 degrees.  Im hoping this shows the manure is starting to heat up,because the probe was down about four inches, and even though it was sunny, it was only about 25 degrees and I don"t think the sun alone would have heated up the soil to that depth. I am hoping I can plant my first seeds tomorrow afternoon. I want to plant celery, celeriac, peppers and a few others that grow slowly. I think I'll wait till about the middle of March for the Tomatoes. I think it would be best if all the sash were made of wood. Also the plexiglass is relly nice to work with, but it's probably expensive in big sheets. My bed is four feet wide but three is probably better. Its probably best to round up the sash or old storm windows and the size your bed accordingly.