[mminer237]

All energy from log burners comes from the fuel, and some ashes remain unburnt. They're under 100% efficient at converting fuel to heat. You put in x fuel and <x heat.

A heat pump takes heat from outside the system. You put in x fuel and you get >x heat. Getting more energy than you put in makes the efficiency over 100%.

[OJFord]

I know. You can't just ignore the bulk of the input and still call it 'efficiency' though.

Even manufacturers call this 'coefficient of performance', not efficiency.

[MichaelCollins]

Since precise use of language is so important to you:

> "You can't [...]"

He did, so obviously he can. You mean shouldn't, not can't.

[OJFord]

Sure, a slightly irritating turn of phrase, not accurate. I didn't think it would be so controversial to hold terms of art/words with actual scientific meaning to a higher standard though.

If we're willing to be so blasé with 'efficiency' then why not, say, 'functional programming'? If it works it's functional right?

[marshray]

An implied qualification of "you can't [while remaining logically consistent]" is common usage.

[bufferoverflow]

> They're under 100% efficient at converting fuel to heat

I think only matter-antimatter reaction comes close to 100%. Burning fuels isn't even 1% of that.