The only time I can imagine a law would require a landlord to include the heat in the OPs situation might be that the gas meter to the unit the tenant lives in has something connected to it that the tenant has zero control over such as a shared hot water heater or say a second apartment that for some reason had say electric or oil heat but a cook stove, or say a gas clothes dryer connected that could trigger a landlord to have to pay that meters charges and include the utility for the affected unit.