The short answer
Yes. You need a valid EPC before you market a property to let, and it must be made available to prospective tenants free of charge at the earliest opportunity.
When it must be in place
The certificate must exist before the property is advertised. Portals such as Rightmove and Zoopla require the rating at listing, and letting agents can be fined for marketing without one.
The minimum rating
Under the Minimum Energy Efficiency Standard (MEES) a rented home in England and Wales must normally reach band E or better. Since April 2020 this applies to continuing tenancies, so a lease signed years ago is not exempt.
Exceptions
A handful of property types fall outside the requirement, including some listed buildings where compliance would unacceptably alter their character, and certain temporary structures. Exemptions are not automatic and usually need registering on the PRS Exemptions Register.
What it costs
A domestic EPC starts at £89.99 inclusive in London.