Plaintiffs appeal from an adverse judgment in their action for a refund of retail sales taxes assessed on the proceeds from their furnace cleaning business.
Plaintiffs are engaged in the business of cleaning furnaces and chimneys in all types of buildings. In addition to using the usual brooms, steel brushes and scrapers, they employ a power vacuum cleaner mounted on a truck. The cleaning for customers is at infrequent intervals and is usually in addition to the routine care of the heating equipment by the customer himself.
A tax commission audit of plaintiffs’ records resulted in a deficiency assessment for retail sales tax on plaintiffs’ charges for cleaning furnaces and chimneys. Plaintiffs paid the assessment under protest, claiming that their business was a “janitorial service” within the exemption of RCW 82.04.050. The tax commission denied plaintiffs’ petition for a refund and this action was filed.
Every retail sale transacted in this state is subject to a sales tax. RCW 82.08.020. Prior to April 1, 1959, a “sale at retail,” as defined in RCW 82.04.050, clearly excluded the cleaning of furnaces. Effective April 1, 1959, the definition of the term “sale at retail” was amended to read:
The term “sale at retail” or “retail sale” shall include the sale of or charge made for tangible personal property consumed and/or for labor and services rendered in respect to the following: . . . (c) the sale of or charge made for labor and services rendered in respect to the cleaning, fumigating, razing or moving of existing buildings or structures, but shall not include the charge made for janitorial services; . . .
RCW 82.04.050.
The tax commission implemented the statutory change by amending its rule 170 to read:
The Retail Sales Tax does not apply to charges made for janitorial services nor for the mere leveling of land used in commercial farming or agriculture. The tax does apply however, in respect to contracts for cleaning furnaces, chimneys or the exterior walls of buildings, as well as to earth moving, land clearing and the razing or moving of structures, whether or not such services are *571performed as incidents of a contract to construct, repair, decorate, or improve buildings or structures.
Further, the tax commission issued Excise Tax Bulletin 3.08.172 which in substance excluded furnace and chimney cleaning from the definition of “janitorial services.”1
It is our opinion that the furnace cleaning activity of the plaintiffs is a janitorial service.
The words of a statute must be given their usual and ordinary meaning. State v. Roadhs, 71 Wn.2d 705, 430 P.2d 586 (1967). Webster’s Third New International Dictionary (1968) defines a “janitor” as one who “keeps the premises of an apartment, office, or other building clean and free of refuse, tends the heating system, and makes minor repairs.” (Italics ours.) The few cases which have been concerned with janitors and their duties are generally in accord with this description. E.g., see Teall v. Harlow, 275 Mass. 448, 176 N.E. 533 (1931).
Considerable evidence was adduced at trial showing that the cleaning of furnaces is a normal janitorial function. Indeed, the trial court stated in its memorandum opinion that it was “satisfied the clients of the plaintiff, through their janitors or custodians or what other name designated, normally clean furnaces.”
But the trial court concluded that an ordinary janitor cleaning out a furnace would not do as thorough, efficient, and complete a job as the plaintiffs, who, using specialized equipment, only clean a particular furnace about once a year. Since an ordinary janitor, using less sophisticated *572tools, would not do as good a job as plaintiffs, the trial court felt the plaintiffs were not performing ordinary janitorial services.
The trial court has confused the means with the object. How a janitor cleans a furnace does not determine taxability. The method or equipment used makes no difference, as long as the object is the same. For example, it is painting whether done by a brush, roller, or spraygun. If one waxes a floor, it is the same whether he waxes by hand, rag, mop, or machine. Technological advances in a particular pursuit do not necessarily change the essential nature and object of that calling. Cleaning furnaces is a janitorial function as indicated by the trial court. The method used does not change the nature of that function. To clean is to clean, whether by hand or machine. Thoroughness is not a valid criterion of taxability.
The services performed by the plaintiffs are similar to those rendered by industrial cleaners who assist the housewife in “spring cleaning.” The industrial cleaners merely perform the normal tasks of a housewife more thoroughly and efficiently by utilizing better equipment. Yet, these services are not subject to the retail sales tax. In both cases, the services are rendered as a matter of convenience and are capable of being performed by the customer himself.
The evidence establishes that one of plaintiffs’ former customers, the Kennewick school system, purchased a power vacuum cleaner from plaintiffs for use in cleaning its own boiler systems. The vacuum is operated by the janitors of the school system. It is not said that the janitors of the school system, when using the special power vacuum to clean the boilers, are not performing janitorial services. This may be an exceptional instance, but it indicates that whatever tools the janitor, maintenance engineer, or building superintendent employs in cleaning out a furnace, it remains a janitorial service.
The tax commission contends that a review of the legislative history of RCW 82.04.050 conclusively shows that the legislature intended commercial furnace cleaning *573to be subject to a retail sales tax. This argument is predicated on the legislature’s silence with respect to the tax commission’s interpretation of the statute, embodied in rule 170. Since rule 170 has been on the books for over 9% years, during which time the legislature has amended this statute five times without repudiating the administrative interpretation, the defendant urges that the legislature has “silently acquiesced” in its interpretation. State ex rel. Pirak v. Schoettler, 45 Wn.2d 367, 274 P.2d 852 (1954), is cited to support this argument. However, this rule of statutory construction is only applicable when the statute in question is ambiguous. Further, the rule is to be applied only in those instances where it is apparent that the subsequent legislative consideration involves the same or similar issue as that which is covered by the administrative rule.
Even assuming the ambiguity requisite to application of the rule of State ex rel. Pirak v. Schoettler, supra, the result sought by the tax commission does not follow. It is just as reasonable to assume ambiguity in the words “cleaning of existing buildings or structures” as it is to assume ambiguity in the words “janitorial services.”
Although interpretive rules and regulations promulgated by the tax commission are entitled to great weight in resolving doubtful meanings of taxing laws, they may not amend or change the enactments of the legislature. Pierce County v. State, 66 Wn.2d 728, 404 P.2d 1002 (1965).
The repeated reenactment of a statute, without repudiating a prior administrative interpretation thereof, is evidence of legislative acquiescence, but it is not conclusive. Legislative silence in such cases is only a factor to be considered. See In re Estate of Bordeaux, 37 Wn.2d 561, 225 P.2d 433 (1950), which involved subsequent reenactments of a statute after a decision of this court interpreting it. It was contended that the legislature had thus acquiesced in the interpretation placed on the statute by the Supreme Court. However, it was held that although the subsequent reenactment of the statute without change was entitled to great weight, it was not controlling.
*574On numerous occasions the federal courts have been confronted with the contention of congressional acquiescence in administrative interpretations of statutes. In many of these cases the courts have had little difficulty in rejecting the contention. In Pacific Power & Light Co. v. Federal Power Comm’n, 184 F.2d 272 (D.C. Cir. 1950), it was said at 275:
At best the reenactment of statutes is a nebulous foundation for statutory construction, and before a mere reenactment can be given conclusive effect as a congressional adoption of an administrative interpretation, it must be shown that Congress was conscious that it was doing so.
The tax commission in the case at hand has not shown that the legislature was conscious or aware of the administrative interpretation of RCW 82.04.050 when the statute was subsequently reenacted. Post-1959 amendments to this statute do not relate to subsection (c) which is before us. This statute is a complex enactment containing many segments and deals with a variety of activities which are made subject to taxation. We do not believe it is reasonable to assume the legislature considered the impact of an administrative rule on a portion of that statute which it was not considering at the time it was amending other portions of the statute.
Before 1943, the definition of “sale at retail” was generally restricted to sales of tangible personal property. In 1943, the definition was enlarged to encompass charges made for labor and services rendered in the construction, repair, decoration or improvement of buildings, but did not include charges for labor and services involved in the “mere cleaning, fumigating, razing or moving of existing buildings or structures.” (Laws of 1943, ch. 156, § 2.) The use of the word “mere,” as the plaintiffs and defendant suggest, indicates a distinction between major construction and the normal maintenance of a building. The 1957 amendment (Laws of 1957, ch. 279, § 1) uses practically the same language. Then in 1959, the legislature included in its definition of a “sale at retail” the charges made for “cleaning, fumigating, razing, or moving of existing buildings or *575structures.” (Laws of 1959, Ex. Ses., ch. 5, § 2.) The word “mere” was omitted. And for the first time, “janitorial services” were specifically exempted.
The omission of the word “mere” in the 1959 amendment is significant and indicates a legislative intent to abolish the earlier distinction between major, unusual and infrequent cleaning of buildings and structures from the incidental, normal and frequent type of cleaning. Thus, for the first time it was called upon to consider the taxing of the activities usually performed by janitors and building maintenance men. It expressed this intent by the express exclusion of “janitorial services.”
We are satisfied the legislature did not intend to tax as a “sale at retail” the charges made for the cleaning of furnaces, which is a normal janitorial service.
The case is reversed and remanded for a determination of the amount assessed as a sales tax against plaintiffs’ furnace cleaning business, which amount is to be refunded.
Hunter, C. J., Weaver, Rosellini, and McGovern, JJ., concur.
The existence and language of the bulletin was stipulated and reads:
“The term ‘janitorial services’ will include, generally, the types of cleaning services ordinarily performed by an employee janitor in the course of his regular duties, whether such types of cleaning services are performed individually under separate contract or are included within a general contract to perform a combination of such services. The term will include contracts to perform window washing, floor cleaning and waxing and the cleaning of interior walls and woodwork, but will not include such activities as cleaning the exterior walls of buildings, the cleaning of furnaces or septic tanks, or special clean-up jobs required by construction, fires, floods, etc.”