The inside width is about 57" as there is about a 1 1/2" on each side. Below is the link to the spec sheet for this unit... http://www.imperialrange.com/nspecificationspage.php?id=1045&mod=323
Thanks for your question. While this Imperial ICMA-60 60" Cheesemelter doesn't necessarily need an Ansul system, this size will require a hood for exhaust purposes. That said, requiring an Ansul system may depend on your current state's health department regulations. It would be wise to check with them also to determine if they require equipment like this to have a fire protection system.