The state and all of its institutions, all political subdivisions, and all public schools, when purchasing coal for heating purposes, shall give preference to bidders supplying coal mined in North Dakota if such coal, on an aggregate basis, will provide equivalent British thermal units of heating value in comparison to coal mined elsewhere, if the total bid price of the coal mined in North Dakota and delivered is not higher than the total bid price of coal mined elsewhere and delivered, and if state air pollution permits to operate would not limit the use of North Dakota coal due to emissions limits. In evaluating the comparable price of North Dakota coal versus other coal, the state and its institutions, political subdivisions, and public schools may include any ash handling costs that may be associated with the use of North Dakota coal. The state or any of its institutions, any political subdivision, or any public school, when advertising for or reviewing bids for the purchase of coal for heating purposes, may not mandate the use of any particular type of coal or the region where the coal is to be mined.