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