The climate in Costa Rica is that of a “tropical savannah”. By definition, this means that the country has a wet season and a dry season. Also, it means that the average temperature in most parts of the country is above 64 °F (18 °C) in each and every month of the year. We are presently in the midst of a very dry, dry season.
The word “tropical” leads to misconceptions. All too many from northern climes assume that the country must be uncomfortably hot and humid. Others assume that it rarely gets uncomfortably cold. They are all wrong. It depends where you choose to live or to visit.
There are many regions in Costa Rica where one can live quite comfortably without either air conditioning or home heating. This is so where we live in the Central Valley at an elevation of about 2660 ft. / 840 m. near the town of Atenas. The average daytime high during 2013 was 84 °F. The average overnight low was 67 °F. The maximum daytime high was about 94 °F but it was accompanied by very low humidity. The minimum overnight low was about 59 °F, but it was accompanied by high humidity. Overall, the result was daytime highs moderated by low humidities - making for daytime comfort - and overnight lows moderated by high humidities - making for nightime comfort.
At lower elevations in the Central Valley average daytime highs and overnight lows tend to creep up and air conditioning might become desireable. But, there is rarely if ever a stifling combination of heat and humidity like that which occurs during the summer in the eastern U.S. and Canada.
Conversely, at higher elevations in the Central Valley and ultimately the surrounding mountains, average daytime highs and overnight lows tend to drift downward. Above 4000 ft. / 1200 m., or perhaps a bit lower, a fireplace or some other form of home heating becomes desirable.
As one moves away from the Central Valley over the mountains and down to the Atlantic and Pacific coastal lowlands and beaches, both daytime highs and overnight lows begin to rise. They are often accompanied by high humidity, making air conditioning a necessity for those who are not acclimatized.