Furnace Efficiency


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Old 11-14-05, 09:08 AM
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Furnace Efficiency

My natural gas furnace (boiler) in the lower level of my bilevel is about 30yr old.
Since, the flame needs air to burn:
Is it more efficient to draw the 60deg air from the lower level (obviously my house has enough leaks and cracks for a furnace to work),
or, would it be more efficient to draw in 20deg outside air?

With outside air the furnace wouldn't draw 60deg air up the chimney,
but on the other hand, wouldn't the flame be hotter and thus heat the boiler water quicker with the warmer inside air?
SteveS
 
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Old 11-14-05, 04:32 PM
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Originally Posted by Skramy
My natural gas furnace (boiler) in the lower level of my bilevel is about 30yr old.
Since, the flame needs air to burn:
Is it more efficient to draw the 60deg air from the lower level (obviously my house has enough leaks and cracks for a furnace to work),
or, would it be more efficient to draw in 20deg outside air?

With outside air the furnace wouldn't draw 60deg air up the chimney,
but on the other hand, wouldn't the flame be hotter and thus heat the boiler water quicker with the warmer inside air?
SteveS
That's a very good question that I have actually wondered about myself.

I have supposed that fire is SOOOO hot that it so overwhelms the temperature of the fresh air being drawn in. And because of this, I have a feeling that the fresh air being drawn into a sealed combustion burner would be more efficient.

Any one else?
 
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Old 11-15-05, 02:33 PM
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I don't have a fact, but they say in the newer sealed (90%) system, it burners hotter and cleaner when it uses outside air..

The air is cleaner, and don't have the household fumes.. and what not in it.
 
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Old 11-15-05, 03:08 PM
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There is just so many BTUs in the Gas for heat.No matter where the air comes from. Just keep the burner clean and set the air on the venturi right

ED My .02 cents
 
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Old 11-16-05, 04:18 PM
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On effiency:

Actually, there would have to be a small increase in temp across the heat exchanger if you were pulling inside air as opposed to outside air due to some of your BTUs would have to heat the cold air up to room temp as opposed to just heating room temp up to whatever, but this would be offset by the amount of outside air that would be drawn into your house due to you venting inside air for combustion.

So in theory maybe, in reality no change.
 
 

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