The hot sleeper is designed to moderate your body temperature for a most comfortable lasting sleep.
Although it has temperature settings down to 8° the cooling unit is not designed to refrigerate your body and it will often not go that low, depending on ambient room temperature.
The heat exchanger that cools the water needs a supply of cool air to work properly. The fan then expels the resulting hot air into the room. This then needs a well ventilated or cool room to work properly.
Extra length hoses are available to place the heat exchanger unit outside the room if necessary up to a maximum of 4.5 metres.
A setting of 25-28° works best in most situations. Although not seeming cold to the touch this moderating temperature is still approximately 10° below body temperature so giving a cooling effect.
In practice colder settings tend to wake a person at night because the body fights the colder temperature by producing heat. The person then wakes and tries to find cool patches in the bed sometimes to seeming little avail.
The higher temperature setting of 25° + also enables the heat exchanger to run quiet and more economically because it is not working so hard.
It is quite different to a room temperature setting because the temperature is conducted through solid material rather than air- as any cook will recognize, the temperature you cook at in an oven is quite different to that in a pot or pan.
In practice maximum variance of temperature setting should be between 20° and 35°. Temperatures outside these settings may also create condensation.