[Peter Finke]

Svein, certainly a valuable supplement.
I am always unsure when seeing these heatpacks. Could they become too hot? Will they loose their heating power too early? Will they get colder continously or at a certain point all of a sudden? I think it need not to fix a definite temperature if they keep things well between 17 and 27 degrees Celsius (better lower than hotter). We would need them especially in winter in oder to avoid the influence of the often freezy temperatures outside. But I am entirely unclear about how dependant they work from the outside temperatures. Of course, styropor boxes are used within cardbord boxes and we must observe that airflow could be passing nevertheless. But sometimes there are outside temperatures of – say – eight degrees Celsius on the positive scale, and sometimes there are eight degrees below the frost line. I cannot understand how the same heatpack could be able to equalize that difference. It seems to me to be a risky play and no secure way of measuring or dimensioning possible.
Or am I wrong?