Hangfire processing load when using with IIS, what process is taxed?

I’m running windows server 2012 with IIS 8.5, I need to run some long running background tasks and I want to avoid taxing IIS with backgroundtasks. I find it a bit unclear what processes Hangfire is taxing when running its tasks. Is it running pure windows threads? Or is it still using the same IIS threads as my webapps are using (and thus slowing down IIS and making it unstable).

Thanks!