A furnished property may have a different market rent from a comparable unfurnished property, but furnishing alone does not automatically give a landlord the right to increase your rent. The landlord must follow the rules applying to your tenancy, including any rent cap, review timing and notice requirements. Those rules can depend on when the tenancy began and whether the property is covered by current rent-control provisions. Check the RTB and gov.ie guidance, and consider professional advice if you believe the proposed increase is unlawful; the RTB can ultimately determine a dispute based on the facts.