In MD, each political subdivision (the counties and the City of Baltimore) must have either its own housing or livability code or use the state "Minimum Livability Code". Some of the codes apply to all dwellings; others apply only to rental dwellings. However, that having been said, every lease contains an "implied warranty of habitability". This basically means that a tenant shall be furnished a rental premises that complies with all health and safety codes of the state/locality. As such, typically a landlord is is responsible for the replacement of or repairs to the electrical, plumbing and heating systems (but there is no requirement that A/C be provided). To be sure of your rights you should contact a tenants rights association near you or contact the local district court (typically the clerk of the court can direct you to help, including landlord-tenant handbooks).