[mbswitzer]

This is my first summer away from our new home in The Villages. Two weeks ago I received an alert from my Ecobee thermostat advising me of high indoor humidity. I remember the guy from Munn’s setting the “high humidity” alert level at 70% and advising me to set heat at 60F and cool at 80F while I’m away. After receiving the high humidity alert I phoned Munn’s to see if 70% indoor humidity was an issue. The person I spoke to said that indoor humidity above 60% may lead to mold / mildew problems. She suggested that I turned the AC on to help reduce the humidity. I incrementally reduced the thermostat setting down from 80F to 68F and monitored the humidity level. After about 24 hours the humidity was below 60% so I raised the thermostat setting back to 80F. Since then the indoor humidity has mainly been in the high 50’s to low 60’s. I’m a bit concerned because this alert happened in the springtime which is nowhere near the hottest and most humid part of the year. I’m hoping I’m not going to have to cool my house to the low 70’s all summer to control the humidity. I’d appreciate anyone sharing their experiences with me on this subject. Thanks!

[mulligan]

What did your homewatch service do when you called them ??

[vintageogauge]

I don't know anything about a Ecobee thermostat but our's has a setting for humidity the turns the AC on to dehumidify if it get's over whatever % we set it at. If you have that feature and set it at 60% that should take care of it. If you don't I would suggest having a separate humidistat installed to keep everything dry.

[dewilson58]

Actually in the summer, your A/C will be running more so it will control your humidity.

Having the A/C we at 80 during the summer, away from home, you will be fine.

What I find interesting.........................Why are their not mold issues in garages??? Hot, humid...........Hmmmmmmmm.

[vintageogauge]

Originally Posted by dewilson58

Actually in the summer, your A/C will be running more so it will control your humidity.

Having the A/C we at 80 during the summer, away from home, you will be fine.

What I find interesting.........................Why are their not mold issues in garages??? Hot, humid...........Hmmmmmmmm.

A friend of ours did just that, set the AC at 80 and when he came back his carpets were buckled. He put in a humidistat and had no further problems. I guess it depends on the weather and how the air circulates in your home.

[tophcfa]

Originally Posted by dewilson58

Actually in the summer, your A/C will be running more so it will control your humidity.

Having the A/C we at 80 during the summer, away from home, you will be fine.

What I find interesting.........................Why are their not mold issues in garages??? Hot, humid...........Hmmmmmmmm.

Agree, our A/C does not have a humidity setting and we keep the house A/C set at 81 and have never had a problem. As cheap insurance we keep a couple of dehumidifiers, with the relative humidity set at 60%, as a back up in case our A/C fails and drain them into a sink/shower.

Good question about why no mold in garage, never thought about that?

[ton80]

Originally Posted by tophcfa

Agree, our A/C does not have a humidity setting and we keep the house A/C set at 81 and have never had a problem. As cheap insurance we keep a couple of dehumidifiers, with the relative humidity set at 60%, as a back up in case our A/C fails and drain them into a sink/shower.

Good question about why no mold in garage, never thought about that?

The key variable in mold formation is relative humidity (RH) not absolute humidity. A garage does not generally have moisture generators such as showers etc, It is generally hotter than the ambient temperature so it usually has a lower RH than the outside air even when the outside air has a higher absolute humidity. The garage can have a higher absolute humidity than your house but a lower Relative Humidity. In Florida there usually are no cold surfaces in the garage that cause high RH unlike partially underground garages in the Northern states. Put a temp/RH measuring device in your garage to see for yourself. The same is true of your attic space. The attic is a good place to dry herbs.

To decrease RH you can increase the temperature thereby raising the dewpoint or reduce the moisture in the air inside your home. These are the reasons that running a standalone dehumidifier will lower the RH quickly. Running the AC alone to reach the RH setpoint when equipped will drive the inside air temp lower along with the RH by condensing and removing moisture in the air exchanger.
I agree with your use of dehumidifier for extra protection and agree with your setpoints. We never had a problem using these settings during our snowbird years.

An unoccupied home set at 80F for AC usually will have RH less than 60% except for long periods of cool rainy weather when the temp does not cause the AC to run. Air circulation is necessary. Keep room doors and closets open.


Some definitions
Absolute humidity is a measure of how much water is present in air inside a closed space. Maximum humidity at a given air temperature is basically the dewpoint. If the air gets cooler or there are cool surfaces drops of water will condense on the cooler surface.

Relative humidity is a measure of how much water is present in the air versus the maximum water that can be carried at a given temperature. Relative humidity is expressed in percent. As stated previously, a relative humidity of 60% is often recommended as a maximum allowable relative humidity to avoid mold formation.

[dewilson58]

Originally Posted by vintageogauge

A friend of ours did just that, set the AC at 80 and when he came back his carpets were buckled. He put in a humidistat and had no further problems. I guess it depends on the weather and how the air circulates in your home.

And maybe carpet.

Two houses, about 10 years each, no issues.

[tophcfa]

Originally Posted by ton80

The key variable in mold formation is relative humidity (RH) not absolute humidity. A garage does not generally have moisture generators such as showers etc, It is generally hotter than the ambient temperature so it usually has a lower RH than the outside air even when the outside air has a higher absolute humidity. The garage can have a higher absolute humidity than your house but a lower Relative Humidity. In Florida there usually are no cold surfaces in the garage that cause high RH unlike partially underground garages in the Northern states. Put a temp/RH measuring device in your garage to see for yourself. The same is true of your attic space. The attic is a good place to dry herbs.

To decrease RH you can increase the temperature thereby raising the dewpoint or reduce the moisture in the air inside your home. These are the reasons that running a standalone dehumidifier will lower the RH quickly. Running the AC alone to reach the RH setpoint when equipped will drive the inside air temp lower along with the RH by condensing and removing moisture in the air exchanger.
I agree with your use of dehumidifier for extra protection and agree with your setpoints. We never had a problem using these settings during our snowbird years.

An unoccupied home set at 80F for AC usually will have RH less than 60% except for long periods of cool rainy weather when the temp does not cause the AC to run. Air circulation is necessary. Keep room doors and closets open.


Some definitions
Absolute humidity is a measure of how much water is present in air inside a closed space. Maximum humidity at a given air temperature is basically the dewpoint. If the air gets cooler or there are cool surfaces drops of water will condense on the cooler surface.

Relative humidity is a measure of how much water is present in the air versus the maximum water that can be carried at a given temperature. Relative humidity is expressed in percent. As stated previously, a relative humidity of 60% is often recommended as a maximum allowable relative humidity to avoid mold formation.

Thanks for the very informative post.

[Laker14]

Another factor working in your favor while you are away all summer is that you won't be opening doors and windows, and allowing an influx of outside air (humid outside summer Florida air) into your house, repeatedly throughout the day. This will assist your AC in keeping the RH down, with less work than if you were actually living there.

[asianthree]

Since 2010 we have kept the air at 80 in the summer. 2019 and 2020, left the air temp, at 77. We have a stucco designer, 2000sf.

Compared each month from 2010 to 2020. Cost at 80 for 9 years, was about $13 dollars less than the last 2 years at 77. What I did notice at higher temps, was anything made of plastic became brittle. Combs, sunglasses, and so on broke when used. 2019 and 2020 I didn’t have to replace anything.

This year we had to get a new system.
Installer said keeping at 77/78 keeps air running a small amount more than at a higher temp of 80, since the house is closed up. So if seco stays about $13 more, a month, keeping house cooler I am good with it, and I won’t have to replace so many sunglasses.

[Djean1981]

If possible, get a dehumidifier (versus having to run the AC real low). We got an "Ivation" model ivaduwifi60, with wifi connectivity. It can remove over 6 gallons of water out of the air in one day. It's programmable and app controlled (from anywhere) and will keep the house humidity to where you want it, without babysitting it. Some people place it in the bathtub, so there are no concerns about drainage. My understanding is that humidity is a concern for newer houses.

[C. C. Rider]

Heating the air in the house or cooling the air in the house will both reduce the relative humidity (RH). The problems with high RH occur when we have extended periods (a couple of days) of moderate temperatures and rainy weather. Under those conditions, neither the furnace nor the AC will run much at all, and this allows the RH to increase inside the house.

If your thermostat has a humidity control, that's great and that should take care of any RH problem. If your thermostat does not have a humidity control setting, then it's a good idea to have a dehumidifier or two in the house.

Dehumidifiers are relatively inexpensive and they have a control where you can select the maximum humidity. They won't kick on until/unless needed. Most houses should probably have two of them due to lack of air circulation when the furnace or AC is not running.

Be sure to get a dehumidifier that saves your settings if the power goes out. Otherwise, when the power comes back on, the dehumidifier will revert to the default factory setting which may not be suitable for what you want. In fact, it may not even come back on at all. That's not good if you're 1,000 miles away.