The portable Buddy from Mr. Heater is a popular propane-powered model. It can crank out either 4,000 or 9,000 Btus (depending upon the setting), and claims to heat spaces up to 200 square feet. Ideal as it might seem, the company warns that it's not recommended for use aboard boats.

After a test report was published in the Jan. 1, 2005 issue on eight small portable electric heaters, a number of readers contacted Practical Sailor.

Several took issue with the manner in which the heat output of the eight heaters was measured. (It was done in two ways: by measuring the temperature of the heat as it emerged from the heaters and again one foot away; and the maximum velocity of the air one foot from the heater.)

Basically, what was lacking in PS's testing routine was a way to determine how well a given heater would warm up a given volume of air. A tiny heater, like a candle, can produce…