steam humidifier leaving white dust inside duct

Nom_Deplume

Hi...homeowner here. We have an Aprilaire 800 steam humidifier, the kind that uses disposable canisters. I have made a plexiglass-covered window in the duct to let me see the steam tube inside the duct. Looking at it as the new humidification season approaches, I find that the steam tube, and the bottom of the duct below it, is covered with a significant amount of white powder. It is not as fine as ultrasonic humidifier deposit, but sort of like that. (I opened up the duct and wiped up the bottom surface and the steam tube using diluted vinegar, and cleaned the holes with a wire.)

This is confusing to me. Ultrasonic humidifiers leave white dust because they are not emitting water vapor, but rather a mist of tiny water droplets. In this case we have steam. How can a gas carry hard water deposits?

The tubing between the humidifier and steam tube is correctly pitched. Everything is within spec as far as I can tell from reading the manual. I would be grateful for any suggestions on what this is due to, and how to fix it.

Jamie Hall

If there is any liquid water carryover -- which there almost certainly will be in a simple steam humidifier -- that will carry some minerals

Derheatmeister

It is probably the calcium in the water Droping out... As the 800 series humidifier needs EC to operate you most likely will have to live with this.

pecmsg

Is the furnace fan running with the humidifier?

Nom_Deplume

Thanks for the helpful comments. There is about 4ft of steam tubing (flexible tubing) carrying the steam from the humidifier to the duct, with about a 1:10 pitch for any condensing water to drain back. I know the water is boiling in the cartridge and this creates some mist, but it seems strange to me that this mist would run 4ft up this tubing along with the steam and end up evaporating inside the duct. But I guess it is possible.

When we got this humidifier, I never understood that we'd have to disassemble the duct and clean inside annually.

EBEBRATT-Ed

@Nom_Deplume

I think you will always get a little bit of that. When the humidifier starts the steam tube will be cold, the air is cold (in comparison to the steam) as is the duct and everything else. As the steam comes through your going to get a little unavoidable condensation until everything heats up

Nom_Deplume

Huh?
Condensed steam is distilled water and does not contain calcium salts (or anything else solid).
To get white powder deposits, tap water (not just steam) must be going uphill from the humidifier to the duct and drying (not condensing) there. That's what is strange about what I am seeing.

EBEBRATT-Ed

Call it what you will. You getting some water carryover when the humidifier is cold

Nom_Deplume

Yes, that is perfectly true.

EdTheHeaterMan

Are you able to collect that white powder and put it in small plastic bags? a few grams each...
Asking for a friend

EdTheHeaterMan

Nom_Deplume said:

Huh?
Condensed steam is distilled water and does not contain calcium salts (or anything else solid).
To get white powder deposits, tap water (not just steam) must be going uphill from the humidifier to the duct and drying (not condensing) there. That's what is strange about what I am seeing.

You are talking about Dry Steam. Dry Steam is when there are no water droplets left in the steam because it is superheated (look up superheated vapor on Google). Wet Steam (that is what your humidifier produces) has some water content. That water will carry some of the minerals that are in the tap water along with it, as it finds its way into the duct.

EBEBRATT-Ed

@EdTheHeaterMan

You explained perfectly what I could not.

Nom_Deplume

EdTheHeaterMan said:

You are talking about Dry Steam. Dry Steam is when there are no water droplets left in the steam because it is superheated (look up superheated vapor on Google). Wet Steam (that is what your humidifier produces) has some water content. That water will carry some of the minerals that are in the tap water along with it, as it finds its way into the duct.

Thanks! I found that hard to believe, but clearly it is true.
Strangely enough, I put in a new canister today and it seems to be producing dry steam---I no longer see any clouds coming out of the steam wand when looking through my duct viewing port. Yet it is humidifying just fine. Hopefully that will reduce or eliminate the white deposit.

SuperTech

Nom_Deplume said:

You are talking about Dry Steam. Dry Steam is when there are no water droplets left in the steam because it is superheated (look up superheated vapor on Google). Wet Steam (that is what your humidifier produces) has some water content. That water will carry some of the minerals that are in the tap water along with it, as it finds its way into the duct.

Thanks! I found that hard to believe, but clearly it is true. Strangely enough, I put in a new canister today and it seems to be producing dry steam---I no longer see any clouds coming out of the steam wand when looking through my duct viewing port. Yet it is humidifying just fine. Hopefully that will reduce or eliminate the white deposit.

That canister should be replaced annually.  I had a feeling that was the culprit