The fundamental factor in relay contact rating is current, not power, so it doesn't really work that way.
Actually, that relay appears to be rated at 12A/125VAC. I do agree that maximum current capacity of the entire unit is dependent on all current carrying components. Relay, PCB traces and terminals. Exactly what is the limiting factor is hard to say. I have inspected a number of different versions of these units and found varying depth/robustness of the PCB traces. It is safe to say that the manufacturers current rating of the device should be used.
Most fractional horsepower refrigeration compressors don't draw 10amps and momentary startup current can usually be discounted if cool delay function is used. Higher capacity cooling components such as window a/c units must be analyzed individually. Heater wattage/current is a design value that must be considered closely. For a fermentation chamber, where slow heating and cooling is preferable, 50w per carboy is more than enough.
The real danger using one of these units comes when someone attempts to use them to directly power a boil element, which should NOT be attempted. A recent thread showed photos of the resulting carnage.
HF32F-G Datasheet
