Adios Pantalones said:
You have to calculate from absolute zero if calculating a % increase/decrease in temperature.
True, but we're not so much concerned with percentage of difference in absolute temperature as in the heat necessary to raise it. Only about 6% of the total heat needed to raise the wood to ignition temp would be needed for those few degrees between outside and inside temps.
The heat loss from melting the ice is significant, but still less than 15% of the heat loss due to evaporation of the same amount of water. Roughly, one BTU needed to raise every pound of water one degree Fahrenheit, 140 BTU to melt a pound of ice, 970 BTU to evaporate a pound of water.
The specific heat of wood is about half that of water, so it only takes about 0.5 BTU to raise a pound of wood 1°F. That means a 5 lb split that is 20% water would have 4 lbs of wood fiber.
Auto ignition temp of dry wood is about 550°F, so it would take 1245 BTU to raise one pound of water to boiling point from a 75°F ambient temperature, and 1900 BTU to get the wood up to 550°, or 3145 BTU total. Add an extra 75 BTU for water and 150 BTU for the wood and you can raise that same split from 0°F to 75°F. That comes out to 3370 BTU... a whopping 1% difference.
Of course, as mentioned above, you only need to get the outside hot enough to ignite, so I say drop in in there at 0° or at 75°. As long as the wood is dry on the outside it should ignite just about as quickly... unless you snuff the kindling fire out by adding too big a load too soon.