Heating, Air Conditioning, Fridge, HVAC/indoor humdity


The past few winters Ive been having a problem with moisture / condensation. We have lived in the house 15 years and as far as we can remember this is just in the past few years. Weve noticed condensation on the windows, pants growing mold. Our house is about 60 years, 1300 sq feet and we have a gas furnace.

 Yesterday I purchased a humidity gauge to measure what we had. Yesterdays (outdoor temperature) was close to 70 degrees with low humidity. When I came into the house the inside temp was about 73 degrees and the humidity was about 61%. Since it was a warm day the furnace did not come on all day. I went into the crawl space and found no signs of leaks (no standing water), the vents were all open and clear. I decided to open a couple of windows and watched as the humidity level quick fell to 51-53 %.  I closed the windows after a couple of hours and although the humidity level rose it stayed at 57% until we went to bed. We did not cook , my wife and I both took short showers and used the exhaust fan. Still the humidity level remained at 57%.

 This morning the first thing I did was check the meter, in the room weve had the most problems in the humidity was 67%, as I walked thru the house some areas were as much at 74%. This morning the outside temp is 57 degrees with 67% humidity. The only thing that changed over night was the furnace was been used.  

Ive read a lot lately about using exhaust fans, venting crawl space. Does the furnace make the air more humid?  Any thoughts would be very helpful.

Heating reduces the RH%, but does not remove moisture from the air.
The colder the house is, the higher the RH% is and the harder it is to control humidity levels when cooling is not being used.  Homes typically have humidifiers where heat is run constantly to keep things from getting to dry.  Vapor barriers work to keep the moisture outside from getting inside though the walls.  Keep in mind that anything or anyone that is inside puts moisture into the air.


Heating, Air Conditioning, Fridge, HVAC

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Craig HVAC Expert


I have been in the HVAC field for the past 18 years. I can help with most HVAC questions. I work on commerical buildings for the most part, and have yet to find anything I could not troubleshoot and repair, when repairable. I work on small 1 ton units to a 2500 ton chiller. Troubleshoot air flow, elect, and control problems. I attend regular classes to keep up with the latest and greatest.


I work on commerical sites, hospitals, gov't buildings. I can troubleshoot just about anything in the HVAC business.

5 years trade school, VFD training classes, Liebert factory training, some York and Trane factory training.

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