Opinion by
These are suits in trespass to recover damages for injury to plaintiffs’ property allegedly caused by air pollution attributable to defendant’s operation of its coal-cleaning plant.1 The trial court by its verdict found for the defendant in both cases and, as provided by Pa. R. C. P. Rule 1048, supported its verdict with findings of fact and conclusions of law. Plaintiffs’ ex*594ceptions to the findings and conclusions were overruled, and these appeals followed.2
The findings of fact, broadly stated, were as follows: The two appellants purchased their homes in 1931 and 1959, respectively. Both properties are located within 1500 feet of appellee’s coal processing plant, which consists of crushers, conveyors, vibrating equipment, screens and picking tables. The plant has been operated by the appellee and its predecessor since 1948, and the appellants realized at the times of their respective purchases that the properties were located in an area generally used for industrial and coal mining purposes. As a result of complaints, appellee installed in 1962 an air cleaner, thermodryer and coal washing unit, and soon thereafter a dust collector and covered coal conveyor. Notwithstanding these measures, the appellee’s coal cleaning operation has contributed to air pollution affecting the properties of appellants from 1962 to the time of trial.3 The appellee has employed specialists in the field of fuel and combustion air pollution who have conducted numerous tests. They have recommend*595ed tbe installation of a certain type of wet scrubber on the thermodryer as a means of reducing emission of dust from that source. This equipment will cost $20,-000 to $30,000. The appellee has adopted the recommendation and “intends to either discontinue using the thermodryer or install the wet scrubber.” “With the installation of the wet scrubber, defendant company will have done everything now known and economically feasible to eliminate any source of air pollution.” The cleaning plant is an essential part of appellee’s mining operations, and appellee is not in default as to compliance with any requirements of the Air Pollution Control Commission.
The trial court concluded, as a matter of law, that the invasion of appellants’ properties by coal dust from appellee’s plant has not been substantial,4 nor was it intentional or unreasonable; neither has the appellee been negligent in conducting its operations.5
Both the lower court and the parties have accepted §822 of the Restatement of Torts as the law governing this case. Our Court adopted that section in Waschak *596v. Moffat, 379 Pa. 441, 109 A. 2d 310 (1954), and it is reproduced in full in the margin.6 In essence, it provides that the owner of private property is entitled to damages due to injury occurring from a nontrespassory invasion of his premises if the defendant’s conduct is the legal cause of the invasion and the invasion is (a) substantial, and'(b) either (i) intentional and unreasonable, or (ii) unintentional, but negligent, reckless or ultrahazardous conduct. The appellants have not been able to satisfy the requirements of that section of the Restatement.
The primary question, as we view it, is whether the trial court was correct in concluding that the invasion of appellants’ properties was not unreasonable when the condition could be cured by the installation of . equipment which had not, at the time of trial, been installed. An actor’s conduct is unreasonable under §822 of the Restatement, unless the utility of his conduct outweighs the gravity of the harm. Restatement of Torts, §826 (1939). Our Court has stated that the actor’s conduct lacks utility if it is economically and technically possible to correct the harm and such steps are not taken. Burr v. Eidemiller, 386 Pa. 416, 126 A. 2d 403 (1956) ; see Herring v. H. W. Walker Co., 409 Pa. 126, 133, 185 A. 2d 565 (1962). The limited record before us does not disclose when the recommendations as to the wet scrubber were made or when this device *597became technically and economically feasible, or how long before trial the appellee had decided that it would either make the installation or discontinue its thermodryer. Since such facts were requisite to show that an invasion was unreasonable and they were not included in the findings of fact by the trial court, it can only be concluded that the appellants did not carry their burden of proof. It is clear, however, that the learned trial judge had before him sufficient facts to justify the legal conclusion that the invasion was not unreasonable: the major improvements in 1962 and the continuing attention to the problem thereafter, culminating in a decision to employ apparatus whereby the appellee “will have done everything now known and economically feasible to eliminate any source of air pollution.”
Since, as indicated above, the posture of this case at the time of decision was an action at law for damages tried without a jury, the court was obligated to render a verdict for either the plaintiffs or defendant; the injunctive or conditional forms of equity decrees were not available. It is clear that the verdict for the appellee was based in part, at least, on its announced intention at trial to install a wet scrubber or abandon the thermodryer. Because the verdict was based in part on an expectation, however, the judgment thereon is not to be considered res judicata as to any damage subsequent to the date of the verdict in the event the appellee has not subsequently fulfilled that expectation or discontinued what otherwise might be considered an unreasonable invasion of the appellants’ property.
Judgment affirmed.
Mr. Justice Jones took no part in the consideration or decision of this case.
Mr. Justice Cohen took no part in the decision of this ease.