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How Humid Is It?

December 1, 2013

This fall, when it was getting cooler but I still had the air conditioner on, I became concerned that it was too humid in the house.  The first thing I did was to read about air conditioners on the web.  I found that they do reduce humidity, but this depends on the the temperature differential across the evaporator coils and the speed of the air flowing over those coils.  They can be ineffective in reducing humidity when they are improperly designed.  As well, they don’t remove humidity well in the fall because the air conditioner seldom runs when the outside temperature is lower.

The next thing I did was to consult my humidity meters.  I have two of these.  There’s an old saying:  “Man with two watches never knows what time it is”.  Well, I didn’t know what humidity it was.  One meter read 70% and the other read 90%.  The one upstairs was a small instrument with temperature and humidity dials.  It was quite old, but the temperature reading was accurate.  That was the one that read 70%.  It confirmed my suspicions that the house was too humid.  The other one was downstairs, hanging on a wall.  It had a thermometer and barometer as well as a small humidity meter.  It was also quite old.  That was the one that read 90%.  I couldn’t believe it could be that humid in the house.  It’d be raining inside at 90%.

To reduce the humidity, I started opening windows at night and on cool days.  Eventually, I turned off the air conditioner and switched to heating.  Of course, the furnace didn’t come on often either, because it was still fairly warm outside.  The upstairs humidity meter did drop to 60%.  That’s still too high, though.  The downstairs meter was clearly wrong.  Maybe the upstairs one was wrong too.  I had heard that humidity sensors were unreliable, and that they became worse with time.  My understanding was that the sensor lost its range of motion as it grew older.

It was then early winter.  The heat was on.  I bought a digital temperature and humidity meter.  That makes three humidity meters.  It was inexpensive, with a single battery that’s supposed to last a year.  More importantly, it read 30%.  That’s too low for comfort.  It was time to start up my furnace humidifier for the winter.  It was a drum type, all caked up with calcium deposits.  I removed the tray and drum, and soaked them in vinegar.  That worked reasonably well, but I soon ran out of vinegar.  I did a final cleaning with CLR and water.  The foam pad was soft enough after those treatments.  I put the tray and drum back in the humidifier and turned on the water.  Next I discovered that the drum never turned when the furnace came on.  Something else was wrong.  I thought about replacing the whole thing, except that that model wasn’t being made anymore.  I read some reviews of furnace humidifiers that were available.  There were lots of complaints, and not many satisfied customers.  I knew I could still get replacement parts for mine, though.  The 24 VAC power appeared when the furnace came on.  The little motor worked.  When I bypassed the humidistat, the drum started turning every time the furnace came on.  It was the humidistat that was faulty.  When I removed it, I found it contained only a sensing element, a transparent plastic ribbon, and a micro-switch, both in a metal frame.  It was the switch that had failed.  I found a replacement humidistat at Home Depot.  It was the same, except that it had a plastic frame and a different micro-switch.  This one actually worked.  After a day of running, my digital humidity meter went up to 40%.  That’s getting close to the comfortable range.

Even better, the setting on the new humidistat agreed with the digital meter.  The old upstairs meter was clearly wrong.  I threw it out immediately.  What about the downstairs meter now?  It had dropped to 70%, still too high.  It also had an adjusting screw on the back.  That screw saved it from being thrown out too.  I adjusted it until it matched the digital meter.  Now it reads correctly, but will it move as the humidity changes?  Maybe the adjustment was only a reprieve.  We’ll see.

Finally, humidity control was all set for the winter.  I’ll have to watch it again next summer when the heat is off and the air conditioner is on.  Soon I’ll have to do something about the furnace humidifier too.  I’ve already replaced the motor once.  I replaced the water valve too.  The drum is broken in places.  What’s going to break next?  People’s experience with new models is not appealing.  I suppose I’ll wait a while longer to see what happens.  It seems that furnaces are reliable but furnace humidifiers are not.

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