Single vs. Two Stage Furnace Efficiencies

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Old 09-27-07, 09:48 PM
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Cool Single vs. Two Stage Furnace Efficiencies

I've been reading about differences between single and dual stage furnaces and I'm very confused. For a 90 (or 92)% efficiency furnace, all the information out there says it's better to get a dual stage because it uses less energy than a single stage. If two furnaces are both 90% efficient, how can one use less energy than the other? Does the efficiency of a furnace vary with load, i.e. does a single stage 90% efficiency furnace not really operate at 90%? Yes, I did read about how the two types of furnaces operate - I'm just stuck on how a dual stage can use less energy (be more efficient) than a single stage if the manufacturer labels them both as 90%. Thanks in advance for any responses.

Stu
 
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Old 09-28-07, 07:35 PM
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Originally Posted by stuart01 View Post
Isays it's better to get a dual stage because it uses less energy than a single stage. If two furnaces are both 90% efficient, how can one use less energy than the other?
It may use less energy since it not short cycling, short cycling is harder on the equipement, and it needs to run about 10 mins or so to reach it's peek efficency. Most 2 stage system use variable speed DC fan motor, they use less elecrticy than a standard blower.

Two stage really is sold on COMFORT, not effciency.
 
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