Aprilaire Humidifier, too powerful a solenoid? Vent ducts noise.

SparklingWaterFebruary 21, 2013

I'd love to get your comments on this. We've lived in this house for almost 20 years without our current vent ducts reverberating such intense noise when our gas furnace turns on with an Aprilaire humidifier.

What's changed is an Aprilaire humidfier configuration: instead of upgrading to the 700, the well regarded hvac company piecemealed an upgrade on the old Aprilaire 760. Dumb me not asking nor them offering a 700 upgrade as it would have cost less in the end. After the first upgrade of rubber tubing to pvc with new filter in case it was splayed, the system stopped working. The next upgrade was a new bigger and brass solenoid (picture below). Since then, whenever the AS dual stage gas furnace engages or turns off, I hear an abrupt clamping down of the Aprilaire humidifier box (seems like two step process) with a big vent duct clanging noise. That sound is driving me nuts, as it travels all through our house ducting.

When the company came because the humidifier wasn't turning on (turned out the upstair humidity was higher than we thought, so they turned the humidistat up higher to 35 to 40), the hvac specialist even heard the new clanging duct vent sound and shook his head saying "those are the hardest to find and resolve". What? It happened on your time!

When I turn off the humidistat and unplug the Aprilaire, the dual stage furnace runs without the objectionable clanging whole house duct noise. Mission accomplished but no house humidifier.

I can't stomach having these guys out again. It took three visits on this humidifier and top dollar and we ended up with a functional yet out dated Aprilaire 760 system, and a horrible, totally objectionable new whole house vent duct noise. It is so loud it makes me wonder if our vent ducts could be adversely affected due to sudden pressure change. I truly think the solenoid may be over powered for the system.

Can you weigh in here on what might be causing this new vent duct noise? Thanks.

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Is there a sail switch in the duct work somewhere?

    Bookmark   February 21, 2013 at 4:20PM
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Ha, had to read up to even know how to respond, weedmeister.

No, no sail switch:

A Sail Switch activates an electronic air cleaner, a humidifier, or other equipment in response to airflow from the system fan.

    Bookmark   February 21, 2013 at 6:50PM
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Hard to say from afar, but I'd trace back the incoming water line from it's source and make sure it's not laying on top of the ductwork. I've seen them "dance" when the furnace kicks on.

    Bookmark   February 21, 2013 at 9:09PM
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Thanks, tinmantu, will do. I turned the Aprilaire off this morning out of frustration and sure enough, with the gas furnace coming on due to the cold not ANY loud duct noise with turn on and turn off.

Hope those weeks of humidifier use haven't jarred any ducts free from their suspending rods or loosened elbows due to the stress: it's a big system down there in a tight space.

    Bookmark   February 21, 2013 at 9:55PM
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Is it a solenoid valve for the water flow into the humidifier? Perhaps it's hammer. Is it a plastic hose, or copper? If copper, and there's a little slack, a loop in the pipe may help, or, if you're handy with plumbing, a tee with a vertical column for an air chamber might help as well.

    Bookmark   February 26, 2013 at 11:39PM
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Ha! I should have left the pics, alan. Hammer is plausible. Yes, it's a BIG brass solenoid (the prior one was much smaller-somehow I think that this change is related to this incredible turn on of fan and clamping down of the Aprilaire box itself (like being sucked into the supply). Water line is 1/4" copper: I'll look to see if I can loop it. Thanks for your help.

    Bookmark   March 1, 2013 at 12:35AM
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