Are Dehumidifiers safe to use and recommended?

[Jeff Charlton]

The first question must be why do you need a DH? The answer is of course because you have excess moisture in the air causing condensation and or your trying to prevent relative humidity going over 70% (, because you mistakenly you may believe that’s a trigger point for mould growth. The reality is 99% humidity in the Antarctic is bone dry while 25% humidity in death valley would be like a sauna. Relative humidity is a function of psychrometrics and temperature and both are related . Mould in a refrigerator is a great e3xample.
Actually in a home a dehumidifier is a mould factory when you consider what it does. Suck in moist air into a warm machine where a cold radiator causes the air to reach Dew Point where the moisture it holds simply condenses and falls to a drip tray where it is pumped or falls by gravity into a receptacle.

You will I suspect immediately realise the condensation, running temperature of the machine an ia warm moist contained area is an ideal environment for mould growth. This is exasperated when you turn off the machine and the omnipresent mould spore is activated

I have tested hundreds of dehumidifiers in clients homes and all blow out toxigenic species after a short term of being turned off.

If contractor’s bring in dehumidifiers to dry your wet home consider where his machine was and what it was doing last week?

[emilybailey]

Would you recommend using dehumidifiers at all?

Under what conditions would you use them?

Would you clean and replace them/filters frequently? Especially if they were brand new?

[Jeff Charlton]

I would use dehumidifiers to dry a building if I had to but there are better ways to dry a water dmaged building.
Few DHs have filters and they are certainly not HEPA.
The coil and drip pan quickly become contaminated.
I wouldn’t have a DH in my home unless it was brand new and single use.
I have shown time and again air particle counts and air bioloogical contamination counts pre and post turning on a DH. They are mould and bacteria factories and people with CIRS shouldn’t use them

[emilybailey]

Thanks for your response Jeff! It goes against what we’d all think but it makes sense. Instead of using dehumidifiers in a home what would you recommend?

Do we need to be concerned about humidity levels then and the levels? Should we simply just open windows etc when cooking showering, and having adequate heading but not too high? What would you recommend in a home instead? Your advice is invaluable, thank you!

[Jeff Charlton]

Sorry for slow response
Always ventilate. You can have 99% humidity in the Antarctic and its dry as a bone , whereas 30% humidity in death valley Arizona is like a sauna . You need to calculate the amount of water in the air with a Psychrometric chart and I will put one up on the forum. Here we measure RH against temperature to calculate the actual weight of water in the air. So its a combination of two factors temp and RH NOT just relative humidity.
Mould needs warmth, no ventilation and moisture (not wet) and preferably NO UV light (sunlight)

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