If LENR where a 1% effect, then we could question accuracy of calorimetry. But it is NOT.
Most of the scientific community still believes that the effect reported is small, so that the existence of the effect is still in question because per cent level effects are presumed hard to measure.
This statement is inconsistent with the 20x or greater excess power observations of Fleischmann and Pons in their early experiments
The early work with open cells claimed high excess power, and there are anecdotal claims of high power surges, but the last from P&F was around 1993. They worked another 5 years in a much better lab with much more funding, and never published at that level (or any level) again in the refereed literature. Then Toyota shut the lab down and Pons abandoned the field. It's pretty hard to base the evidence for cold fusion on claims the authors themselves were unable to confirm with improved experimental protocol.
When McKubre and others used much more reliable calorimetry, he was down in the percent level. That's why in 2001, Jed Rothwell, an active advocate for cold fusion, wrote: "Why haven’t researchers learned to make the results stand out? After twelve years of painstaking replication attempts, most experiments produce a fraction of a watt of heat, when they work at all. Such low heat is difficult to measure. It leaves room for honest skeptical doubt that the effect is real."
So when it comes to the sort of published claims that advocates can get behind, it is a small effect in the range of a few per cent. And this is evident in this exchange as well, where Lomax falls back on McKubre's result of a fraction of a watt at a few percent of the input.
and it is inconsistent with more recent work. There are a great many reports of subsequent observations of excess power bursts where the excess power is 50% to 300% of the input power, as well as a smaller number of reports of excess power events with very high power gain between 1000% and 3000%.
True, there are some claims of high power gain, and even some with infinite power gain, and some with relatively high absolute power. But these are not in peer-reviewed literature, and most are from companies looking for investment. Advocates tend to emphasize peer-reviewed papers in their advocacy, but claims of *any* excess heat in the refereed literature in the last decade are scarce indeed. And the few that exist claim on the order of a watt of power or less, representing a small fraction of the background chemical or input power, and well within the range of calorimetry artifacts. Indeed, the excess heat claimed in Arata-type experiments around 2009 has been examined by Dmitriyeva et al., who found it was attributable to chemical, and not nuclear effects.