My personal suggestions to anyone, and even being very new to home theater, that Denon and Marantz run really hot seems to be a consensus.
If you plan on keeping this unit for a while, which we assume you would, you can buy a AVR cooler.
you got two options,
AC Infinity
If you want to spend more money and get a pretty product.
CoolerGuys
If you want real performance to keep your unit ice cold. I use the 4 fan setup, it has more airflow vs AC infinity 3 fans.
Second, I choose CoolerGuys because you can easily change out the fans to any fans you like. If the fan dies you can replace it very easily.
You also have the option of putting Noctua fans, which will have you running at sub zero temps practically. They are the strongest industrial grade fans. But they run at 30 a piece.
I paid 59.99 for my CoolerGuys vs 120 for the AC Infinity. Currently on sale for 69.95, great deal, link below
I run my AVR usually 4-8 hours per day, the unit is never hot and I got a Marantz 7013.
CoolerGuys Comcool stand deluxe 4 fan with variable control CCS 120-4M
www.coolerguys.com