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Stopping Scale In a Humidifier

by Mark Timmons January 14, 2012 21 Comments
Humidifier Question: I have a steam humidifier and it is constantly plugging up, and I have to clean the chamber all the time in the winter. Is there anything I can do to help this? Would a water softener help? - Signed C.C. Answer: C.C., Steam humidifiers are unquestionably the best way to humidify your household (or business) air if you live in a climate where that is needed. However, in 98% of the country, the water requires treatment and I do not mean a water softener. The problem with steam humidifiers is that most water has some degree of mineralization in it. The minerals are calcium and magnesium, and when water is heated and evaporated by the stream humidifier it leaves the minerals behind. After a few cycles, if the evaporation chamber contains 1/4 gallon of water, it has the minerals of 4 or 5 gallons (maybe more). This creates big problems. A water softener is not the answer because it works by exchanging the calcium and magnesium for sodium. Instead of calcium and magnesium buildup, you will have sodium buildup. Solutions - on a Scale of 1-10:
  1. Polyphosphate - Some companies have filter cartridges that install on the inlet to the humidifier and "coat" the humidifier with a layer of sodiumhexametaphosphate which is supposed to help. Bad Idea! Rating: 1
  2. Salt-Free Water Conditioners - They don't take out the calcium and magnesium so the problem still persists. Rating: BIG ZERO!
  3. Deionization - You can use a DI cartridge to remove all of the minerals, but it is very expensive. It works extremely well, but costs 35 to 60 cents a gallon (depending upon water hardness). On a scale of how well it works, it's a 10! On cost, it's a 2. Overall Rating: 5
  4. Reverse Osmosis - Unless you have more money than sense, reverse osmosis is the ONLY way to treat a humidifier economically. Some people even put a DI cartridge after the Reverse Osmosis system to have absolutely pure water, but in most instances Reverse Osmosis removes 98% of the dissolved solids and allows the humidifier to work without the burden of all the hard minerals.

Conclusion: If you don't have a reverse osmosis system on a steam humidifier... or any humidifier for that fact, you are doing a very bad thing! PUT A REVERSE OSMOSIS SYSTEM ON ANY HUMIDIFIER - YOU WILL BREATHE EASIER AND THE SYSTEM WILL LAST A THOUSAND TIMES LONGER!

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February 05, 2017 Rob

Our humidifier also runs on hard water and is constantly clogging . Does someone make an inline demineralizer for just the humidifier? Thanks!

November 19, 2017 Mark Timmons

Yes, you can use something like this: but the odds are the cost will be 40 to 50 cents a gallon.

This cuts the cost to about 5 cents a gallon:

November 21, 2017 Parren McNeely

I believe an automatic flushing timer (AFT) would minimize sodium build-up and be considerably more efficient than using reverse osmosis (RO) water. AFT would add roughly 1.5 ( 1-1/2) gal/day to water use by flushing humidifier at regular intervals whereas RO effluent would double-to-quadruple overall water consumption, depending on RO unit efficiency. (On the article’s Scale of 1-10, I’d give it an 11 or 12 overall, since AFT is also so much more affordable than RO)
I’d give RO a 7 for effectiveness, since its low pH water gradually erodes copper plumbing and possibly the humidifier heating element. But if using RO system, it should at least have a permeate pump to maximize unit efficiency. On cost, its about a 5 or 7 depending on whether or not it has a permeate pump. (Overall Rating: 6-to-7)
Thank you everyone for the intriguing discussion, it has been most helpful in my research.

March 10, 2018 Mark Timmons

Sounds like a lot of work when you can just install an RO system and NO a residential RO will not erode the copper or the element. That is misinformation.

March 11, 2018 Minoe

There is a fundamental flaw in this article: RO water has very low conductivity and thus severely impedes the ability of an electric steam humidifier to operate. The process of boiling the water requires the water to conduct electricity between the electrodes in the steam vessel. RO water simply does not have enough conductivity to allow the water reach a boiling level in any reasonable amount of time… or ever.
RO is great for a heated element style steam humidifier but not for an electrode style steam humidifier.


April 24, 2018 Mark Timmons

The article was written quite a few years ago when heated elements were the rage! A blog is a living, breathing thing. We will likely update it.

April 28, 2018 JAMES GAMBIER

have a Desert Spring drum type furnace humidifier it gets choked up with calcium in very short time of operation
it is very hard to clean. do you recommend that I use a flow through humidifier I know it is easer to clean and

March 08, 2019 Mark Timmons

I would use a humidifier that can use reverse osmosis water – I do and have ZERO ISSUES!

November 15, 2019 Tim

In response to Minoe’s post, RO is not good in all heated element steam humidifiers either. In mine (EWC/Field Controls S2020), the water level detector requires conductivity through the water probe to detect if it is filled before heating. I’ve thought of adding an RO system to mine but it just won’t work. We have a sodium based water softener and the deposits are an issue, even though the S2020 automatically purges old water daily. As soon as I hear popping when the humidifier starts up, I know that it’s time to clean the heating element again because of caked deposits.

December 15, 2019 power pumice

It’s remarkable designed for me to have a site, which is
useful designed for my know-how. thanks admin

December 22, 2019 Mark Timmons

Sure, if you steal the distiller and have free electricity.

December 22, 2019 spydie

Why not use distilled water? You can’t afford to buy it in the stores, but you can get distillers for your house. Wouldn’t this be cheaper than plugging up the RO membrane with sodium?

January 12, 2020 Kim

I am looking at the Aprilaire 800 steam whole house humidifier. I wrote the company and they said to absolutely not use RO water with their system. They wrote “RO water is extremely reactive and can actually disintegrate our aluminum water panels as well as the electrodes inside our steam canisters”. Can you suggest a whole house system that will work with RO water?

January 15, 2020 Mark Timmons

I cannot say for sure that it will disintegrate the water panels or electrodes, but I will take their word for it. It used to be that steam humidifiers worked exceptionally well for years, but I know they say not to use RO water in them. I recently replaced mine with an Aprilaire power humidifier 700 series and feed it with RO water. It works great and costs less than the steam humidifier. I am no longer sold on steam.

September 08, 2020 Sarahwilliam

Thanks for sharing such an informative post.

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