Energy Usage, Conservation and Weather Stripping - White powder from gas heating system

I hope this is the right forum to ask an HVAC question. I have gas fired heating furnaces in my home. There is a fine white powder that is deposited on all surfaces from the upstairs furnace. It is almost like a coarse talcum powder. You can't see it coming out, but after dusting, it only takes a few hours for the powder to be back. It also does not appear to come from the system when it is the cooling mode in the summer. It does not appear to be coming from the downstairs system. The filters have all been replaced. Can you suggest what the problem might be and how to correct it?

First does this unit have a humidifier in it????? Any leaks in the attic that can take air in??? Dont do it in AC. The AC is the best filter there is cause of the very wet coil there . It will stop most dust cause of the wet coil.

Agree on humidifier!

The system does not have a humidifier in the system. However, there are two small room humidifiers running in two seperate rooms. The system appears to be tight without any leakes. The powder only appears in the heat mode. I am not sure I understand the comment about the wet coils. Can you add further thoughts? Thanks for your support.

My appologies! I do now understand what you meant about the wet coil while in the Cooling mode.

The best filter in the world is the AC running making the A coil in the blower wet with the humidity it takes out of the air. As the air pass over the wet coil and dust will stick to it. I know of lot of people that will turn on and run their AC when the pollen from the trees gets real bad . As just the air filter will not get it all in the home.;)

Can you tell me what the white powder is? It seems to be connected to the humidifiers in some way as there is no white powder downstairs and there are no humidifiers downstairs. What can I do to get rid of the powder upstairs and keep the humidifiers?

What type of humidifier are you talking about? Mineral deposits will build up in most types, and usually they turn on when the furnace is heating (drying the air).

When water is evaporated to make humidity, the minerals that were in the water stay and accumulate.

The humidifiers are small cool mist units that stand alone in the room. They are not connected to the HVAC system in any way. They are relatively new and the evaporative wicks appear to be clean. There are no deposits that are visible in the bottom of the trough that has the water where the wicks have about an inch immersed in the water. They are advertised as not producing the white powder. There are no other humidifiers and there are none connected to the HVAC. The white powder only shows up in the winter when the heating mode is operating. It does not show up with the downstairs unit which has a seperate HVAC unit. I am suspicious that the powder is connected to the humidifiers in some way as it only began to appear after these units were acquired and placed in operation.

I believe it is the two portable humidifiers that are the cause. I just saw an ad of a German made humidifier that claimed it does not create white powder. Check to see if the instruction manual says any thing about changing the water.
Here is what I think is happening:

When water evaporates, it leaves the minerals behind. Each time you top it off, adds more minerals until the water gets saturated with the minerals and then finds a way to release the minerals into the air. I think hard water has more minerals then soft water, so that could be also part of the problem.

Here's what I would do:
Shut down the portable humidifiers and determine if they are the problem. Then go over the servicing manual for information on maintenance. Consult with the manufacturer.
I think when you start up the humidifiers again, you may need to completly remove all the water and fill with fresh water more often instead of topping it off. Also check the wick for any deposits and if you find them, let the wick sit in a white vinegar solution for 24 hours and then rinse and install.
FOR WHAT ITS WORTH:
I used to have a salt water fish tank with corals and needed to dose calcium for the corals. I must have dosed too much because white powder was forming on all surfaces near the fish tank. I had to adjust the dose to solve it and do 25% water change each day for four days to correct the water chemistry.

Thank you for all your help and suggestions. I will begin the process to see if I can solve the problem.

While you are troubleshooting, place some pans of hot or room temperature water close to or on top of heating discharges if you can. Even a pan of water will still evaporate some without the addition of a heat source. Good Luck.