Furnace humidifier - How to power?

I used to have an Aprilaire bypass unit at our previous house. I liked it very much, but they are only available through contractors. Our last one cost about $450 installed.
I just purchased a Honeywell HE260 from Home Depot for $199 (there is a $30 rebate offer in effect until Nov.). It's quite similar to the Aprilaire in styling etc. I've got it bolted to the furnace (Lennox G2 - I believe) and the water supply connected.
Problem: The HE260 comes with a big honking 30VA transformer and a kludgey "sail switch" (relay with a big "sail" that floats in the cold air return and closes when air is flowing...Honeywell's way of sensing blower activity). I want to avoid installing the transformer (24V) and sail switch and, instead, just power the 24V solenoid water valve from the furnace itself.
I doubt the solenoid draws more than about 500 mA. Is there any reason I should NOT try to power it from the Y/T terminals (compressor contactor) at the furnace's low-voltage terminal strip, which provides 24VAC when the blower is on?
-Pat
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Joseph E. Meehan

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Same here in NJ. I bought my Aprilaire at a shop that sells/installs fireplaces, wood stoves, etc. I just walked in and bought one, took it home in a box.

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Pat Coghlan wrote:

Well, the technically correct way to get the answer is to see if the present xformer in the furnace has a current (or VA) rating marked on it, then measure the current that transformer puts out when it is driving all loads which can possibly be placed on it simultaneously. If that shows that the transformer has power to spare, then you could then add on the humidifier's solenoid valve and see whether the current drawis still below the xformer's rating.
But how about this? If the blower motor runs from 120 volts you could just wire the primary of that "big honking" transformer across it and power the solenoid from that transformer. The contacts which control the blower motor must surely be robust enough to take a little additional load.
HTH,
Jeff
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My name is Jeff Wisnia and I approved this message....

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Well, running an outlet to the transformer is one thing, but there is also the sail switch which requires another hole to be cut in the cold air return.
I e-mailed Honeywell, but there reply was "oh, then you're touching the furnace, we can't help you there". I wonder if they take the same attitude towards defence contractors: "oh, then you're interfacing to the jet engine, we can't help you there".
The wires to the solenoid are hanging right by the low voltage strip, so I'm really tempted to just wire it to the Y/T.
Jeff Wisnia wrote:

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Get a model 50 and be done with it.
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I assume you want the humidifier to run only when the furnace is "in heat". If you wire it to the blower motor it may run whether the furnace is heating or cooling. A typical blower motor is multi-speed, with different motor wires used to determine speed. Usually a slower speed for heating mode and a higher speed for cooling, and you would connect it only to the blower motor lead used for heating. However, you may find that the humidifier runs regardless of which blower speed is selected due to a "back circuit" through the motor.
One common way to get around this issue is to use a "current sensing relay (avail. at HVAC distributors). It clamps around the low speed blower motor wire and closes a switch contact only when the blower is in slow (or heat) mode. These contacts can be used to activate the humidifier.

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The humidistat can can turned down in summer to ensure that the unit doesn't come on during the cooling season.
I believe our furnace has only one speed.
The Y/T terminals are energized when the blower is running. You've suggested a different type of relay, to avoid installing the clunky "sail switch", but I'm still determined to power the unit from the low-voltage strip on the furnace.
I will see if I can find a spec for the transformer on the furnace, to see if it can handle 30VA (that's 30 watts, if I remember my high school physics). I guess I should just ask Lennox if the transformer can handle 30 watts.
Joe Fabeitz wrote:

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I guess if you already know everything, you don't need to ask for help.
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Hi Joe, hope you are having a nice day
On 29-Oct-04 At About 01:18:55, Joe Fabeitz wrote to All Subject: Re: Furnace humidifier - How to power?
JF> I assume you want the humidifier to run only when the furnace is "in JF> heat". If you wire it to the blower motor it may run whether the JF> furnace is heating or cooling. A typical blower motor is JF> multi-speed, with different motor wires used to determine speed. JF> Usually a slower speed for heating mode and a higher speed for JF> cooling, and you would connect it only to the blower motor lead used JF> for heating. However, you may find that the humidifier runs JF> regardless of which blower speed is selected due to a "back circuit" JF> through the motor.
You should never wire to a fan speed wire on a multi speed fan as you will burn out the transformer.
-=> HvacTech2 <=-
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Big deal, it is available at hvac supply stores at @ < $100. They don't ask for ID, if you know what I mean!
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