Intermountain Gas Co. has filed a request with state regulators to lower natural gas rates by an average  of 4.5 percent for residential customers. The company filed paperwork with the Idaho Public Utilities Commission last week. If approved, company officials point out it will be the fifth price reduction in the last four years. Company calculations show residential customers who use gas for space and water heating will save an average of $2.24 per month, based on typical weather and usage under the new rate structure. The reduction for commercial customers is projected at nearly $11 per month, or 4.8 percent. Executive Vice President Frank Morehouse says favorable market conditions and prices for gas is driving move to lower rates. The company serves more than 300,000 customers in Idaho.