English to Russian Social Sciences Energy / Power Generation

Доклад о возобновл. источниках энергии.

Secondly, the heating equipment may have been
designed for the high temperatures enabled by fossil
fuels, since higher temperatures render smaller sizes
of the heating equipment and hence, lower investment
costs. This problem can arise regardless of the specific
heating equipment utilised to warm a building up, be it
a hydronic system or air. In either case, a type of heat
exchanger will be needed between the district heating
network and the indoor air, for example, radiators in a
hydronic system.

Не совсем понимаю, как примером "indoor air" могут быть "radiators"...

Спасибо.