I live in Florida, an incredibly wet environment where it's very difficult to get moisture out of house without using a dehumidifier 24/7, which is too expensive. Would charcoal briquettes be of any use?

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    $\begingroup$ No, and even if the briquettes were able to absorb water, they'd be saturated in a day, and then you'd have to dry them or replace them, far more expensive than A/C. $\endgroup$ – DrMoishe Pippik Aug 5 at 23:11
  • $\begingroup$ I know this wasn't your question, but it might be helpful: Dehumidifiers differ in their energy efficiencies. You might want to make sure yours is on the high side (you could check the Energy Star rating; you can also check Consumer Reports if you have a subscription). And you probably already know this, but there are several things you can do to optimize your dehumidifier's efficiency (keeping it away from walls to ensure maximum airflow, keeping the filter clean, etc. -- you can search for more detailed info. online if you're interested). $\endgroup$ – theorist Aug 6 at 1:52

The body of your question shows that your primary concern isn't charcoal's hygroscopic character per se but it's suitability as a practical means to lower the relative humidity inside your house.

Let's start with it's hygroscopic character: It seems that charcoal indeed displays hygroscopic properties (the propensity to absorb water to itself) to some degree (at least to the extent that it affects it's burning properties).

The subject was treated by this paper, wherefrom the following citation was selected as part of this answer to your question:

The charcoal samples placed in the environment with high relative humidity showed an increase in humidity by the heightened final carbonisation temperature, with the highest average detected for charcoal produced at 750 °C. This was the reason why the charcoal produced in this temperature showed higher moisture related to higher porosity presenting a larger area available for water condensation inside the pores.

The difference between the moisture adsorbed by the charcoal packed in two environments can be attributed to more water molecules present in the humid atmosphere (RH = 98%) and a greater ease of inducing the porous region of the charcoal. This means that the more humid the environment, the greater the adsorption of moisture by charcoal.

These two different moisture conditions represent different possible situations of charcoal storage where high relative humidity is not ideal.

Now if one of the reasons you would like to use charcoal over other means of lowering the humidity inside your house is that you were planning to re-use the charcoal later for it's primary purpose (as a fuel), this means that it wouldn't suit that purpose very well, at least if you don't plan to dry your charcoal as an intermediary step in the process (dehumidify > dry > burn). Water requires a lot of energy to evaporate which would waste fuel if you wanted to use it directly as such after using it for your house.

Now for absorbing humidity, there are other (much better) substances you could use out there: You could for instance use the very safe and well known SiO2 form frequently referred to as "silica-gel", which works very well at higher RH levels, and can be conveniently "recycled" by ~ 1h pass in the oven at ~100-120C. The main weakness of silica gel in your case is that it quickly loses efficiency at higher temperatures that are not uncommon in Florida. If you'd like to be a slightly less conventional, one could recommend Calcium Chloride (CaCl2), a fairly cheap substance which will hold up to ~4 molecules of water for each of it's own up to a temperature of 45°C, and at the very minimum 2 molecules of water for each of it's own at any temperature naturally encountered in Florida.

I hope this helps!

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    $\begingroup$ Desiccants are not practical for whole house dehumidification. $\endgroup$ – MaxW Aug 6 at 4:09
  • $\begingroup$ Desiccants need to be cycled, which I agree can be impractical, but I firmly believe that CaCl would be more practical than coal. Without using desiccants, condensating the water would be the only practical option. $\endgroup$ – Veritas Aug 6 at 5:22
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    $\begingroup$ Here's an application that will dehumidify your home and provide running water: nature.com/articles/s42004-018-0028-9 :-) $\endgroup$ – Buck Thorn Aug 6 at 6:56
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    $\begingroup$ A couple of comments: it's $\ce{CaCl2}$, and the mole ratio looks much less attractive when translated into a weight ratio. $\endgroup$ – Buck Thorn Aug 6 at 6:57
  • $\begingroup$ @BuckThorn That is correct, not sure why I wrote it wrong (twice!) $\endgroup$ – Veritas Aug 6 at 8:48

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