Google Home has supported playing radio through TuneIn since launch. Simply ask it to play a local AM/FM or internet station, and it will start streaming in seconds. Now it looks like Google is in the early stages of rolling out support for iHeartRadio.
Earlier today, Google updated its list of supported services on the Home to include iHeartRadio. Asking it to play most stations seems to result in the standard "It isn't available or can't be played right now" message. I was only able to get one local FM station to actually play, but you can try it for yourself by asking "Play [station] on iHeartRadio."
I expect this will be officially announced and rolled out sometime in the next few days. In the meantime, you can always cast to the Home from the iHeartRadio app or use TuneIn.