"Eric Tonks" ) writes:
I have never figured the concept behind a two stage furnace, except as a
marketing gimick. If you need heat, when you need heat, -- you need heat.
Getting half the heat seems pointless. I imagine you need a special
expensive thermostat to choose half heat or full heat. Or do you have an
outside thermostat that kicks the full heat on if the outside temperature
goes down a lot, that seems the only logical way to set one up. Personally,
getting full heat for 5 minutes vs. getting half heat for 10 minutes, is not
worth the extra cost and complexity, and I sure wouldn't notice the
difference unless the furnace could not supply enough heat.

I have a 2 stage and pretty much agree with this. There are probably some
marginal efficiency gains and perhaps wear and tear gains, but no doubt
not enough to justify the higher cost. The biggest practical difference
might be the furnace noise level. On low power really can't hear it run.
On high, there is a bit of a roar. I don't much care, but for some
people the noise issue might be worth paying money for. Now when I say
"roar" the furnace is still much quieter than its predecessor.

Jonathan