Hygrometer vs Humidistat Readings

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Old 01-12-08, 09:24 AM
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Hygrometer vs Humidistat Readings

Hygrometer vs Humidistat Reading

My in house hygrometer constantly reads a higher relative humidity than my humidistat. The method I use is to adjust my humidistat mounted on my furnace until I hear a click and then look at the reading. The difference can be 15% depending on when I check it.
I know the accuracy of both instruments can be an issue. However, my question is, assuming both instruments are reliable, is it common for the humidistat on the furnace to read a lower relative humidity than an in house hygrometer? I should add when I checked the reading, the furnace had been off for some time to give the air time to stabilize.

Thanks,
Jerry
 
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Old 01-12-08, 09:31 AM
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Be kinda hard to tell what one is right.. But look at it this way.

The humidistat that on the duct is reading that the air is in that area, and a pretty good avg reading from the whole house where ever the returns are at.

The hygrometer is in one spot, and only reading that is in that area.

Like my reading on my one in the hallway reads about 35% now, and in the kitchen that reads 42%. But when I bring the two tgether, it's read the sames.
 
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Old 01-12-08, 01:32 PM
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Jay

In an earlier post on dehumidification you wrote:

Originally Posted by Jay11J
It depends on where you are at.

-Blower ramp delay.

Will be good in area where humidity isn't extreme, and your budget don't allow you to do a higher end control But you can use a basic humidistat.

-Humidistat control of blower speed.

Is good in area where humidity can be high, and where days are wet and mild when you don't have a lot of cooling demand.

However, I would still like to get your comments on my question of having both options installed. And, I know both options perform the same function. When the HVAC person installed my humidistat, he removed my delayed timer without telling me. I would like to know, from a technical viewpoint, if having the two options installed was a problem.

Jerry
 
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Old 01-12-08, 02:10 PM
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What brand of furnace or air handler do you have there?

I have a Trane myself, and I left the timer on along with the humidistat control.

I like the ideal of the quiet slow ramping up even tho the humidity may be lower than set point.

I have heard, but not sure if this a fact or not, if you got the delay along with the humidity control, the blower is going to run a much slower speed, and may cause flooding of the compressor if the system does not have a TXV on the A-Coil.
 
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Old 01-12-08, 03:21 PM
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Originally Posted by Jay11J View Post
What brand of furnace or air handler do you have there?

I have a Trane myself, and I left the timer on along with the humidistat control.

I like the ideal of the quiet slow ramping up even tho the humidity may be lower than set point.

I have heard, but not sure if this a fact or not, if you got the delay along with the humidity control, the blower is going to run a much slower speed, and may cause flooding of the compressor if the system does not have a TXV on the A-Coil.
I have a Rheem Prestige Series modulating furnace. I talked with the tech later about removing my delayed timer. The only answer he gave me was when he checked with whomever, he was told that it was an either or, but not both. I got the feeling that both installed options would be an overkill. I do know that the timer was set for a 7 minute delay before it went to full speed.

Jerry
 
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