hvac system

For those more familiar with hvac systems in Houston, Texas with house built in 1998, my daughter says at nite occasionally she hears drips in attic. I know the secondary drain to the a/c evap. coils are near her window but I am not using the a/c system now. I am using the house furnace (heater) at nite and wonder if it has any condensation that goes out the drain pipe??? I went in attic saw no leaks, water or sounds. I even checked the ceilings too. I think she hears something just not sure what. She says it only seems to appear at nite so I'm thinking now a critter tho I saw no signs of holes in the side of house or sounds in attic. I know it could be also on the roof instead of the attic. I realize that I need to go into the attic when she hears the sound.
I guess what I'm asking is do heaters throw off water from condensation under normal operating conditions?
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On 1/27/2012 11:33 AM, Doug wrote:

But metal heating/ac ducts make "dripping" noises as they warm and cool. The metal in the joints move against each other and where the ducts are touching wood.
Paul
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Are you saying the OP's daughter is hearing things that arent' there?
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That is just plain wrong. Any of the modern condensing, high efficiency furnaces which are common today produce water. It's a product of combustion. It has to be drained somewhere just like the condensate from an AC drain.
If the furnace is a condensing one, then that water could be what is being heard.

I've heard lots of ducts make noise, but would not characterize those as sounding like a drip.
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Have you considered that it may simply be condensation dripping down from the roof shingles when it gets cool outside.
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