(a)  Manufactured and Mixed Gas. - The heating value of manufactured gas and mixed gas, including LP Gas mixed with air, shall be considered as being under the control of the utility, except that natural gas when mixed with manufactured or LP Gas for peak shaving or emergency purposes shall not be considered a mixed gas.

(1)           The average heating value on any one day shall not exceed or fall below the standard total heating value (see Rule R6‑5(1)(a)) by more than five percent.

(2)           The monthly average heating value shall be not less than the standard total heating value.

(b)  Natural and LP Gas. - The heating value of natural gas and undiluted, commercially pure LP Gas shall be considered as being not under the control of the utility.

(c)  When Appliances to Be Readjusted. - The utility shall determine the allowable range of monthly average heating values within which its customers' appliances may be expected to function properly without repeated readjustment of the burners. If the monthly average heating value is above or below the limits of the allowable range for two successive months, the customers' appliances must be readjusted in accordance with Rule R6‑18.