(a) Sales of fuel oil (as differentiated from sales of butane and propane gases) are classified as retail and nonretail sales as follows:

(1) Retail sales—all sales of grades No. 1, No. 2, and No. 3 of fuel oil direct to housholders for their own domestic uses;

(2) Nonretail sales:

(i) All sales of grades No. 4, No. 5, and No. 6 fuel oil as these heavy oils are “special purpose” goods to which the retail sales concept has no application (See § 779.321);

(ii) All sales for resale including such sales to peddlers and other dealers (See §§ 779.331-779.334);

(iii) All sales made pursuant to a formal invitation to bid (See § 779.328(d)).

(b) In some cases the retail or nonretail status of an establishment may turn on sales other than those listed above. In such cases all the facts relative to such sales shall be considered in arriving at a determination. The classification of such sales depends upon whether they are recognized as retail sales. In such cases particular attention shall be given to the quantities involved and the prices charged.