Whats the worst that could happen

[Mike_Schmidt]

if I left my A21 on all the time in a colder room with the vents shut off.

[Space]

[Peter Nielsen]

if I left my A21 on all the time in a colder room with the vents shut off.

If no other gear is stacked on top of the A21, you should be fine :T

No, it won't burn down the house, unless your "room" is a 2x2 closet or something...

[Mike_Schmidt]

Thanks Peter for being left on so much it is no hotter to the touch than my old Cyrus gear that was supposed to be on all the time. Will this prematurely kill this amp though or not?

[Peter Nielsen]

Thanks Peter for being left on so much it is no hotter to the touch than my old Cyrus gear that was supposed to be on all the time. Will this prematurely kill this amp though or not?

No. The killer is other gear stacked on top of it, or rack mounting without sufficient airflow. A free-standing amp can safely be left on...