NSN 4520-01-468-7112, Heater, Space / Barracks, Tent, Non-Powered, Liquid Fuel (burns JP-8 or kerosene directly from a 5-gallon can, approx 1 gallon / hour).  This is the most effective tent heater ever introduced through the Army supply system.  It is completely legal, vents its exhaust fumes out of the tent, and meets all Army safety regulations... which "jet heaters" do not... see below.  Basically a modernized, simplified (fewer parts) Pot Belly stove, it will heat an entire Battalion TOC (approx 4 SICPS tents or a 2-section TEMPER tent) to a steady 60 degrees, on a sub-freezing day.  It takes 5 minutes to put into operation once your tents are in place.  You can purchase it through the Class IX (motor pool) supply system for about $400, or on an IMPAC card (try 888-201-6785) if authorized by your approving official.

There is a smaller model (4520-01-478-9207) which is best used in a GP-Small, or single SICPS, or Soldier Crew Tent.  It costs approx $1,060. 

Army regulations for tent heaters have become more stringent in recent years, due in large part to deaths and injuries caused by (a) improperly vented heaters, which expelled their fumes directly into tents, leading to carbon monoxide poisoning; (b) unsafe heaters, which caused fires; or (c) ineffective heaters, which due to their poor performance caused Soldiers to perform unsafe acts in order to stay warm.  The problem is that very few heaters in use today are safe, effective, and portable. 

Space Heater, Arctic:

Many units purchased powerful kerosene-fueled "Jet Heaters" in recent years, due to the need to keep TOCs (and other facilities) as warm as possible, in order to keep Commanders and CSMs in the best possible mood.  While these heaters produce a loud, satisfying blast of heated air, similar to an M-1 tank's exhaust, they are highly unsafe, because of reasons "(a)" and "(b)" above.  In addition, they require large quantities of 120-volt AC electric power, which is not always available in field environments.  For this reason, they're a bad thing.

Duct-type heaters are another option, but they are large, cumbersome, and generally require a trailer of their own.  They also take an unacceptably long time to set up and tear down.

For our money, the large space heater listed at the top of this page is the best way to go.  This page's author has many years of experience deploying to winter environments, during two sub-zero Korean winters, December / January NTC rotations, as well as 2 tours in Kuwait / Iraq, and has not yet seen a superior heating system.  The best part is that they're free, when you order them through the supply system.  (If the supply system is back-ordered, use your IMPAC card.  The heater made by Hurricane Heaters and can be purchased from many sellers online.)