SAP Host Agent Installation 
SAP Host Agent is installed automatically during the installation of all new SAP system instances based on SAP NetWeaver 7.0 including Enhancement Package 2 or higher.
You only need to install SAP Host Agent separately in the following cases:
There is no SAP system or instance on the host.
The SAP system running on the host is based on SAP NetWeaver 7.0 including EHP1 or lower.
You have upgraded your SAP system to SAP NetWeaver 7.0 including Enhancement Package 2 or higher and the upgraded system does not yet have an SAP Host Agent.