The plaintiff, Mr Sintes, was the owner of a patent claiming an invention in respect of improved features of a wood fuelled stove. The plaintiff alleged that the defendant’s Matai DVI 165 wood fuelled stove infringed claims 1 and 10 of the patent. The defendant counterclaimed for a declaration that these claims were invalid and not infringed. It also sought an order revoking the patent.

The interesting feature of the case lies in the decision of the Court on the obviousness ground and the application of obviousness principles to the patentee’s claim that the inventive step in the patent was the combination of features. In particular what was the position where there was an element of trial and error on the part of the inventor?  Could this still lead to invention? Were the claims obvious?

The key integers of claim 1 of the patent were the following:

a)  A solid fuel stove of the type including an enclosed insulated firebox into  which solid fuel may be inserted through a closable door;

b)  the firebox being collected to atmosphere by means of a flue through which exhaust gases can escape from the firebox, via an exhaust duct at the top of the firebox, adjacent to the front of the firebox;

c) wherein the stove includes an air intake in the form of a jacket surrounding  the flue;

d) such that in use combustion air is drawn from the atmosphere and down the jacket into the firebox, being preheated by the heat of the exhaust gases in the flue;

e) and wherein said jacket is in communication with a primary air duct which is  arranged to receive a major portion of the intake air and to supply said air to  the lower part of the front of the firebox.

The defendant failed in its first invalidity challenge that the claims were not new as a result of (i) prior patent specifications; (ii) an article and photograph in the Christchurch Press newspaper; (iii) disclosure to a workshop company which worked on the plaintiff’s prototypes; and (iv) finally a public demonstration of the stove to certain local body candidates.

The key battle ground in the case came to be whether the alleged inventive concept comprising the combination of features was obvious. (Separately the Court looked as to whether the alleged concept confined to the double vent flu was obvious. But this latter feature was found to be known at the priority date.)

The Court was satisfied that the claimed invention was a combination of known elements. This led to an application of the Supreme Court of New Zealand decision in Peterson Portable Sawing Systems Limited v Lucas [2006] 3 NZLR 721 and in particular the principles of collocation. These are that two old integers do not become an invention simply because they are combined. But if the two integers interact on each other so that there is synergy between them, they may constitute a single invention having a combined effect.

With this case, a difficulty facing the Court was that it was common ground that all the elements of a stove interact with each other in a synergistic fashion. Fogarty J found that, once the idea of bringing outside air down the flu of the fire (and preheating on the way) was understood, it was an obvious step to continue its preheating around the firebox before the majority was released at the top of the door of the firebox. It was well-known that this was a very practicable way of delivering combustion air to the seat of the fire. Because the goal was to reduce particulate emissions from the solid wood fire, the designers skilled in the art would line the inside of the firebox with firebricks so as to increase the temperature and therefore increase the chances of complete combustion of volatiles, thus lowering emissions. Some sort of baffle would be used to belong the presence of gaseous volatiles in the firebox.

The Court found that the patentee did use knowledge general in the art when placing the exhaust duct adjacent to the front of the fire and made the following statement in relation to what happens where there is nonetheless trial and error involving known elements:

[195]  Returning back to the test of "obvious" in s 41(1)(f) Patents Act, I do so with an interpretation of Lucas that it is the policy of the law to be cautious in the case of combination patents. I apply the standard "obvious" as assisted by the standards "known" or "used" and conclude that what Mr Sintes did was use knowledge general in the art and of prior use in the Kent Log Fire when placing the exhaust duct adjacent to the front of the firebox. He was also using knowledge general in the art when combining all the elements of the firebox together with the element known from August 2001, the use of the double vent flue. On that basis, although what he did was not predictable, and even though it cannot be said confidently that the placement of the exhaust duct would be obvious to the skilled man, it did not require a degree of invention. It was the result of trial and error. Had I not been required to follow a cautious policy, I might have found that the defendant had not proved that the exhaust duct and its placement was obvious.

Fogarty J went on to find that claims 1 and 10 were obvious. Further, the defendant’s solid wood fire was not an infringement of claims 1 and 10 in any event.