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Indoor Air Quality

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I live in southern KY where outdoor RH levels reach well over 80% every day during the spring and summer months. I like to keep my house cold... very cold. I keep it between 64 and 66 degrees in the warmer month's, and as low as 48 degrees in the colder months, as I just don't turn on the heat. I have 2 dehumidifiers and they keep the RH at or below 50%. I have an older house with single pane windows that always have condensation them in the mornings. This usually goes away with the sunrise and throughout the day. I realize this is due to the temperature difference between the inside and outside of my home. I have a known mold problem in my crawlspace due to excessive water getting under the house and have made some changes to allow the water to go towards a sump pump which empties it out. Due to money restraints I am unable to have the mold problem addressed however, I am doing what I am able. My question is would it be better so far as indoor mold pollination and spreading to increase the indoor temperature or does keeping the temperature level indoors under 66 degrees inhibit mold growth? I have read that mold doesn't pollinate well above 66 degrees.

Great questions.  The most important factor in controlling mold growth is the relative humidity.  This is far more important than the temperature.  For example, it is quite common to find extensive mold growth on framing during construction in the winter months.  Mold can easily grow in temps down in the 40s.   On the other end of the spectrum, mold grows quite well in tropical climates with 90+ degrees temperatures.  Unfortunately, mold thrives in just about any temperature that a human would find remotely comfortable.  Keeping your home at 66F vs. 72F will make little difference.

The only potential problem with keeping your home cold during the summer months is condensation near the HVAC registers and on the ducts beneath the home.  Moisture and subsequent mold growth can occur when you have a large difference between the two temperatures.  I recommend periodically inspecting these areas to ensure you’re not encountering condensation and dripping.

The key factor is the relative humidity.  In the summer, the only solution (in your climate) is air conditioning or dehumidification.

In the winter months the primary solution is heat.  Each degree you drop in temperature leads to an increase in relative humidity.  While a house can theoretically operate in very cold temps – it will take intense efforts to minimize condensation.  Therefore you have to options – 1.) Increase the temperature (and ventilation) until you stop seeing condensation 2.)  Increase ventilation and dehumidification.  Note – standard dehumidifiers are not effective in cool temperatures. You’ll need a desiccant style dehumidifier to succeed in <60F temps.  These are expensive to purchase and operate.  In most cases, you’ll be better off simply increasing the temperature and ventilation.  Ventilation can be improved by replacing your bathroom exhaust fan with a constant flow unit such as a Panasonic WhisperGreen.


I recently purchased a home, and my girlfriend lived in it for a few months and started to feel ill. She had a mold test done, an ERMI. It showed we had aspergillus ochraceous mold. I did some cleaning and installed an allergen filter into my forced air furnace, and I’ve replaced it multiple times. Recently we retested, another ERMI, and the results came back even worse than the first one. How should I proceed?

ERMI testing is not a reliable indicator of current mold problems within a home.  It was designed to assist in research scenarios where you’re attempting to determine the long term load of mold spores in the air.  It is completely inaccurate at determining the current quantity of mold spores in your air.  Please check out our explanation on our ERMI testing page.  I highly recommend 5 minute non-viable mold air sampling such as an Air-O-Cell cassette.  This is the gold standard for the industry and can provide actionable results.