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I think i'm being sold bunk by a mold company, but not sure.

We live in the tropics, we recently had our bathroom ceiling flood due to a burst pipe, and went away immediately after. (the landlord had the bathroom ceiling removed a bit under a week into our holiday)

Before we left, we called a mold control company and said we were going to leave the A/C on to keep the humidity down to prevent mold growth (we have a new A/C, very efficient, was going to keep it on the lowest setting just to dry the air a bit, so the energy usage would not have been a concern). They said not to do that. They're the "experts" so we followed their advice.

When we returned, the apartment had bloomed (literally bloomed) with mold.

Our landlord now is saying that this is because we use the A/C a lot (we don't), and need to open the unit windows more, and buy a dehumidifier. If we actually did use the A/C a lot, wouldn't the cooling and drying of the air have prevented the mold growth more than opening the unit?

We live next to a rainforest, so I would've thought that opening the unit would invite spores and damp air in rather than prevent mold?

Thanks in advance for any help

Yeah, that advice was super wrong. Moisture encourages mold growth.

After a water leak you need to go to extremes to dry the air to get wet things to evaporate into the air, which you then continue to dry. I would run dehumidifiers, or shoot, if your house has A/C, just run the A/C since that is a dehumidifier.

The only risk is if you excessively chill the air, because cooler air has less capacity to hold moisture. This drives the British crazy, their masonry buildings often have utility spaces with "the damp" which are 40-50F (5-10C) and freon dehumidifiers just don't work well at those temperatures. They are forced to heat the space just so the dehumidifier will work effectively. I've witnessed it myself, a dehumidifer that fills in 8 hours at 75F takes a week to fill at 45F. The goal is measured in gallons, and time is a factor, so that is a total lose. And mind you, dehumidifiers do heat the space since all the energy they use winds up in the room as heat. Air conditioners remove the heat.

So you need to also heat the house, which fortunately is something solar load (i.e. The sun hitting your roof) does automatically. All you need to do is have a system whereby the air conditioner doesn't cool the house more than it's being heated by the sun... Some sort of, gosh, I don't know, thermostat :)

Oh yeah, you have one of those. Set it aggressively enough to run a lot, but not so aggressively that you create the British problem. Something like 60-ish (16C), let it go nuts.

You are being sold.

The evaporator coil in the AC condenses water vapor in the air. It does this by blowing the warm air from your home over the cool evaporator coil. The cool coil pulls the moisture from the indoor air, removing it and draining it from your home via the condensate array. This happens with every air conditioning cycle. If the AC unit can't keep up with the humidity, the air will feel clammy and cool when it should feel dry and cool.

Get a humidity measuring tool so you always know what it is at (generally around $10 US). I don't know how bad the mold is but if it only on the surface, run the AC and in the meantime put on a respirator and use a bleach mix to remove/kill it.

It is possible for A/C to cause mold issues but it depends on a few factors. The problem is this: when choosing a A/C unit for a home, often people (even 'professionals') will assume that bigger is better. The installer plugs in the numbers to the manufacturers model and comes up with a recommended unit size, then bumps it up to a larger one.

The problem with this is that the larger unit will cool the home too quickly. It comes on, cools the air down and then shuts off. But because it only ran for a short time, the condenser did not have a chance to remove much moisture. Now you have cool, damp air in the home which results in moisture condensing in the walls. It may be the case that the mold control company has been called into to deal with such issues and that led to them giving that advice.

In order to dry the house out you need to have the A/C running continuously. Setting it on low (higher temperature) may lead to the A/C cutting on and off and if you have an over-sized unit and/or it isn't especially warm outside, it could make things worse. Setting the A/C to the lowest (warmest) setting that still keeps it on continuously is what you should do if you want to get your house bone dry.

Here are some references that discuss and help explain the issues caused by oversized units:

• https://www.cooltoday.com/blog/3-problems-caused-by-an-oversized-air-conditioner


• https://aristair.com/blog/hvac-humidity-control-5-reasons-your-ac-is-ineffective/


• https://airexpertsnj.com/knowledge/entry/air-conditioner-not-dehumidifying-well-a-new-jersey-tech-explains-why


• https://energyair.com/signs-ac-system-large/


• https://trustcompleteair.com/signs-your-air-conditioner-is-too-big-oversized/


• https://www.greenbuildingadvisor.com/article/coping-with-a-wrong-sized-ac-system

It can, but not for the reasons you think

Mold needs two key components to go wild like that

1. Moisture


2. A cool atmosphere

Your A/C can encourage mold growth by not running. If you leave your HVAC unit on cool and the surrounding air gets cool (i.e. a winter cold front blows through), the moisture in your house will condense and feed the mold. Then, when it warms up, the A/C starts up again, but now it's blowing the spores around. The humidity drop will help deter more growth, but what's there has to be dealt with to make the space habitable again.

We live next to a rainforest, so I would've thought that opening the unit would invite spores and damp air in rather than prevent mold?

The mold spores are already inside, A/C or not. Don't think of it as "letting more in". The issue with an open window next to a rain forest is humidity.