Kerosene appliances -- and kerosene heaters, in particular -- use a specific type of wick. The user manual for a Toyotoma Kerosene portable heater states, "never use any fuel other than clear or red colored kerosene" in the stove.
Wick Differences
Wicks differ even among models of kerosene heaters. Using the wrong wick can result in smoke, clogging, fumes and general unsafe conditions. A wick that will work well for kerosene might not work appropriately with alcohol.
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Differences in Volatility
Alcohol tends to ignite more quickly than kerosene. An appliance calibrated for kerosene may not be able to handle the quick, intense heat. A small amount of brandy on a dessert such as plum pudding creates a dramatic effect because of how quickly it flames up and because it burns away equally quickly without harming the dessert. A wick that has been saturated with too much alcohol could flare up in an even more dramatic fashion.
Efficiency
The same amount of kerosene as alcohol will return more BTUs when burned. If a heater were calibrated to safely use alcohol as its main fuel, it would take about 30 percent more fuel to warm the same amount of space.
Fuel State
Most alcohol stoves use solid or gelled fuel rather than liquid. Stoves designed to burn kerosene have a reservoir for liquid fuel, and their wicks are not designed to deal with a fuel source that needs to be melted or warmed before burning.