GRETO - manufacturers of heating equipment need to properly identify just what "efficiency" they're referring to, in their glossy literature. Typically, number tossed around is the highest percentage value they can find, and that's combustion eff. Most customers don't know the difference between things like combustion eff, boiler eff, system eff, etc. Most sales people don't know the difference either. That's simple ignorance. For the ones that DO know the difference, but don't talk about it - that's deceit.
Propective customers should ask "Just how, exactly, is this efficiency number calculated?" The vast bulk of the answers will fall into two catagories: blank stares/silence, or the longest string of nonsense you've ever heard.
Most of my work involves steam systems. In addition to the efficiency question, most end users should also ask a question regarding "payback". I've seen cases where a whole new $100,000 hot water heating system has been proposed because it was "more efficient" than the old steam system. The main culprit behind the high cost of running the steam system, was a big condensate pump had a failed coupling, so the condensate had been merrily running to a floor drain for at least a couple of years. What's the right solution - re-do the whole heating system for a $100 K, or spend a couple of hundred dollars to fix the pump? The steam system won't be quite as efficient as the hot water, but the payback for the coupling is probably about an hour, vs at least 10 years the conversion, now that the existing system is funtioning properly.