Researching Grow Station 2 Update

I decided that I would monitor the effectiveness of the heating mat over a longer period of time and without keep opening the door and letting what ever ambient heat there was out and the cold air in the shed. So I took readings at 11:00am and again at 5pm so that's a six hour period twice as long as previously, and here are the results

Tray           1      2      3     Mat
11 am    - 2.8 / 3.0 / 2.9 /   2.9 outside temperature 1.7 Celsius I then turned mat on

  6 pm    - 8.5 / 6.9 / 7.8 / 15.8 outside temperature 2.7 Celsius
Increase  5.7 / 3.9 / 4.9 / 12.9                                  1.0

Average Increase in trays = 14.5 / 3 = 4.83 - 1.0 increase outside = 3.83 Celsius which is comparable with the three hour results and I don't anticipate it getting better with the current set up.