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Old 02-08-2014, 08:14 PM   #1
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Aprilaire 600M Humdifier Wiring


I just finished installing my first whole house bypass humidifier(Aprilaire 600M). The last part of the install is to wire it up. Since it has a manual humidistat, and a 24V solenoid, and I have a new high efficiency Trane XB90 furnace with HUM terminals, seemed easy enough.

Issue I'm having is that the furnace board puts out 110V at the HUM terminals so I need to use a transformer to 24V. The Aprilaire manual says DO NOT WIRE TRANSFORMER INTO FURNACE BLOWER CIRCUIT. Why would they say such a thing? Isn't that the purpose of the HUM terminals?

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Old 02-08-2014, 08:23 PM   #2
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Aprilaire 600M Humdifier Wiring


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I just finished installing my first whole house bypass humidifier(Aprilaire 600M). The last part of the install is to wire it up. Since it has a manual humidistat, and a 24V solenoid, and I have a new high efficiency Trane XB90 furnace with HUM terminals, seemed easy enough.

Issue I'm having is that the furnace board puts out 110V at the HUM terminals so I need to use a transformer to 24V. The Aprilaire manual says DO NOT WIRE TRANSFORMER INTO FURNACE BLOWER CIRCUIT. Why would they say such a thing? Isn't that the purpose of the HUM terminals?
did the himidifier come with a transformer..if it did wire the transformer leads to the control board mark hum terminal and neut....then your 24 volt circuit... ben sr

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Old 02-08-2014, 09:10 PM   #3
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Aprilaire 600M Humdifier Wiring


Wire the transformer to the HUM terminals if it has 2 of them. If it has one then that is HOT and the other side of the transformer/neutral goes to the furnace neutral/white. The reason they don't want you to use the blower terminals is because there are 3-4 different speeds for heat and AC etc and if you use one of them then it will be energized and backfeed power to the transformer when the other speeds are used and damage it. If you have a variable speed/ECM motor then it is impossible anyway.
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Old 02-09-2014, 01:51 AM   #4
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Aprilaire 600M Humdifier Wiring


Works like a charm!

The supplier I bought the unit from told me it's ok to use the venting hole for the drainage tube. Is this ok or it going to be too much of an obstruction? It fits snug.

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Old 02-09-2014, 03:41 AM   #5
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Aprilaire 600M Humdifier Wiring


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I just finished installing my first whole house bypass humidifier(Aprilaire 600M). The last part of the install is to wire it up. Since it has a manual humidistat, and a 24V solenoid, and I have a new high efficiency Trane XB90 furnace with HUM terminals, seemed easy enough.

Issue I'm having is that the furnace board puts out 110V at the HUM terminals so I need to use a transformer to 24V. The Aprilaire manual says DO NOT WIRE TRANSFORMER INTO FURNACE BLOWER CIRCUIT. Why would they say such a thing? Isn't that the purpose of the HUM terminals?
The HUM terminal is actually not art of the blower circuit. Its an isolated separate contact on the furnace board.

Long ago, you were suppose to use the 120 volt that feed the furnace, and use a sail switch to prevent the humidifier from coming on without the fan running. But people got lazy, and went cheap and decided to just use the blower line. The back fee from the blower motor would burn out the transformer.

So the makers of furnaces started having their furnace boards made with HUM terminals to prevent this. But the warning label is still in most furnaces.
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Old 02-09-2014, 08:56 AM   #6
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Aprilaire 600M Humdifier Wiring


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Works like a charm!

The supplier I bought the unit from told me it's ok to use the venting hole for the drainage tube. Is this ok or it going to be too much of an obstruction? It fits snug.

This is NOT a good idea as that fitting needs to be open to allow the furnace to drain properly. Go to HDepot and get a tee fitting and cut it into the side of that pipe and add a elbow. They should have some PVC pipe also or stop by a plumbing shop and they can sell you some or get it from a plumber friend.
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Old 02-09-2014, 09:32 AM   #7
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Aprilaire 600M Humdifier Wiring


You do not want to shorten that vertical pipe as on some furnaces it needs to be a certain height/length above the ventor/exhaust fan.
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Old 02-09-2014, 09:53 AM   #8
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Didn't like it either, will do today. Thanks again.
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Old 02-09-2014, 10:44 AM   #9
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Aprilaire 600M Humdifier Wiring


Even better go to HDepot and get some cheap garden hose or clear plastic hose ( they sell it off a roll by the foot) and run the hum drain to the floor drain and not to the furnace drain.

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