An up feed steam heating system has the heating units _____.

In an up feed steam heating system, the heating units are located above the main steam line. This configuration allows steam to rise naturally due to its lighter density compared to water, which enables it to effectively reach the heating units located above. The design takes advantage of gravity to facilitate the flow of steam upward to the radiators or other heating elements, providing efficient heating distribution throughout the system.

Moreover, placing the heating units above the main line ensures that the steam can travel directly to the units while minimizing the risk of water hammer and other issues that can occur in a steam system. The steam's ascent allows it to condense back into water, which then flows back down to the boiler or return line, completing the cycle. This arrangement is critical for the proper functioning and efficiency of an up feed steam heating system.