Humidifier installed on return air duct - normal?

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Old 02-10-07, 12:50 PM
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Humidifier installed on return air duct - normal?

I had to replace my Aprilaire 56 humidistat. This caused be to look at some installation instructions....
Is ti normal to have a humidifier installed on the return air duct 2 feet above the air filter? I have an Aprilaire 560.
Is it normal that the humidistat is located almost on the same height on a side wall of the return air duct?
 
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Old 02-10-07, 02:45 PM
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I am not familiar with the 560 but my 768 powered unit is mounted on the return air duct about 5 feet off the floor. The humidistat is located about three feet UPSTREAM from the humidifier. Seems to me there's something in the manual about the necessity of locating the hstat upstream. You need to be checking the return air humidity, not the air that's just been humidified, right?
 
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Old 02-10-07, 10:57 PM
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It is normal to put them on the returns.. Most of them do this for "Just in case" problem happens. That way if there is a problem, water won't get into the furnace and damge the board or other parts.. Where the return, you just got the air filter.

Fan powred unit should go on the supply side since the air is "HOT" and helps the water evap. quicker. I seen one or two in my life with on the return due to limited area on the supply.
 
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Old 02-11-07, 06:38 AM
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Originally Posted by Jay11J View Post
It is normal to put them on the returns.. Most of them do this for "Just in case" problem happens. That way if there is a problem, water won't get into the furnace and damge the board or other parts.. Where the return, you just got the air filter.

Fan powred unit should go on the supply side since the air is "HOT" and helps the water evap. quicker. I seen one or two in my life with on the return due to limited area on the supply.
That all makes sense, in fact mine is on the return because there's no room on the supply duct.

But what about the control being too close to the humidifier? Isn't that likely to affect the humidity readings? The way I read the post he's got the humidifier on the "wide" side of the duct and the stat may be directly adjacent on the "narrow" side of the duct, at a 90 degree angle from the discharge of the humidifier.
 
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Old 02-11-07, 08:09 AM
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Good eyes Arg.

You are right, the humidistat should go up stream from the humidifer.. It can be thrown off if it's that close to the unit now.
 
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Old 02-11-07, 08:15 PM
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Unhappy Maybe it's me, but......

I have more experience with bypass type humidifiers, but shouldn't a fan powered humidifier be on the return? If not wouldn't the force of the supply air blow the humidity out of the humidifier rather than the fan blowing it in?
 
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Old 02-11-07, 08:22 PM
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Idealy the fan powred unit should be on the supply duct due to the warmth to help with the humidity.

if it goes on the return, should have hot water going to it to help add humidity.

There is a small fan inside the unit that pulls the air from the side, and over the pad.
 
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Old 02-13-07, 07:45 PM
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bypass vs. fan-powered

The bypass unit relies on the pressure differences between supply and return duct to allow heated air to flow through water pad, thus evaporating some of the water (yes, there is somewhat of a viscious cycle here).

The fan-powered unit installs on the supply duct. Very little water would evaporate if it were not for the little fan motor that draws heated air across the water pad and returns the moist air back into the plenum.
 
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