Constrained devices are a common factor in the Internet of Things (IoT). These devices have limited RAM and ROM memory, reduced battery, processing capacity, and transmission power. In consequence, these devices may not work properly with traditional Internet protocols like TCP and HTTP, which were not created for constrained scenarios. However, in 2015 the Internet Engineering Task Force (IETF) published the newest version of the most popular application protocol on the Internet: HTTP/2. It has significant improvements over the previous version, such as binary frames, multiplexing of streams, priorities, flow control, among others. In this work, the parameter of HTTP/2 window size is evaluated in terms of use of CPU, use of memory, response times, and energy consumption for constrained devices in IoT. With this work, we expect to promote the discussion about the utilization of HTTP/2 for IoT and to contribute to an eventual standardization.