What to set thermostat (A/C) in empty Florida condo?

redcurlsFebruary 23, 2014

We go back and forth from Florida to a northern state every couple of months. We have obviously been leaving the thermostat setting too high because we have been seeing signs of mildew on our last few returns. I don't want to waste money cooling a place more than necessary, but don't know what the proper temperature setting should be. Any ideas? We will also be leaving several ceiling fans running and the thermal draperies pulled to protect against the major heat gain we get. Thank you.

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Ceiling fans won't have an appreciable effect.

An appropriate thermostat setting depends to some degree (pun not intended) on what is the typical ambient during the absence period. Assuming you're referencing the summer season, or a non-winter period, the A/C system needs to run enough to maintain a reasonable indoor humidity level.

    Bookmark   February 23, 2014 at 6:57PM
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What temperature have you been setting the thermostat? Where are you finding mildew?

    Bookmark   February 23, 2014 at 8:33PM
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My many seasonal neighbors (Stuart area) keep theirs at about 82.

A humidistat does help.

    Bookmark   February 23, 2014 at 8:36PM
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And I absolutely agree with running your ceiling fans!

    Bookmark   February 23, 2014 at 9:36PM
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Yes, I should have included more info. Thanks for asking. I've been setting the thermostat on 84. Obviously, it's too high for the amount of humidity we get down here. I found signs of mildew in the living room which is the center room of our ground floor unit. It adjoins the warmest room in the condo,which is a Florida room. The Florida room has two 72" wide windows and gets sun from dawn until noon. Down here in the tropics, it can easily be 75 degrees at 6 AM and goes up from there. We DO have solar blinds on the windows and thermal lined draperies. Another room that had mildew was in the bedroom which shares a wall with the living room. It seems to form a musty/dusty grayish film on certain surfaces and has the telltale smell of mildew. I thought the ceiling fans would help with circulation of air, not temperature. Thanks again.

    Bookmark   February 24, 2014 at 12:19AM
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No higher than 80 but really the humidistat is the best idea and solution for your issue. Ceiling fans do nothing about humidity control. Just good for stirring the air.


    Bookmark   February 24, 2014 at 6:37AM
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Running ceiling fans when there's no one in the rooms to benefit from effect of the moving air (fans cool by evaporation of moisture from the skin) would increase the room temp slightly from the heat of the running motor and *technically* ever-so-imperceptibly-more from friction of the blades against the air.

    Bookmark   February 24, 2014 at 7:11AM
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High humidity and mildew is usually a sign of an over sized AC. The capacity of the AC is supposed to be designed to cool the house to 75 on a hot day. Your AC may have been over designed and setting the AC at 84 is making the problem worse. The AC is probably short cycling which means it does not run long enough to dry out the air.

You need to lower the thermostat so that it will run for longer periods of time. The other option is to install a thermostat which monitors humidity so it will turn on the AC when the humidity goes above a specified level.

If you have a wireless router in the house, then consider getting a thermostat with WiFi. This will allow you to monitor the temperature and humidity while you are away. You could even change the settings in case you get some unusual weather.

If you have very high ceilings (10 feet +) then the ceilings fan will help circulate the air. Otherwise I don't think you need to leave them running when you are not there.

    Bookmark   February 24, 2014 at 8:21AM
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Excellent idea from Mike about the WiFi thermostat. Make sure it can both monitor and control humidity in the home.


    Bookmark   February 24, 2014 at 8:24AM
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And again re ceiling fans, mildew occurs when moisture is allowed to remain on surfaces such as walls, the drain pipe inside a front loader washing machine, etc, etc.

Promoting air flow will hasten evaporation of the water and help prevent the moisture remaining on any given surface.

Not sure why the resistance to increasing air flow in this thread, I have not said it reduces humidity... just that it helps prevent mildew formation by promoting evaporation.

For the OP, give a call to a Mildew or mold abater and ask the question - if you doubt yourself as to using the fans.

    Bookmark   February 24, 2014 at 9:18AM
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I think the ceiling fans would help the mildew situation, but I don't know how much.

The key question for me is would it to be better to run the ceiling fans 24/7, or turn them off and use the energy savings to run the AC to a lower temperature?

    Bookmark   February 24, 2014 at 10:31AM
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I agree in principle, however a typical ceiling fan uses 60-80 Watts on high speed. Run at half or slow speed we know that it would require 1/8th of that. :-)

10 Watts for the fan continuously is peanuts.

I am skeptical abo0ut UV lights for this application, but it could also be explored.

In any event, one of the large power companies has conducted a study on what do do about a vacant home in their service area as the OP is not alone in his behavior and in aggregate those folks have a HUGE effect on aggregate electric usage.

    Bookmark   February 24, 2014 at 11:03AM
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Leaking ducts may be sucking moist air into the house if the ducts are located outside of the house envelope (attic or crawl space). Where is the mold appearing?

What you really need is a dehumidifier. Check out this study. There may be others and it would be worth your trouble to study this issue a little.

Here is a link that might be useful: Vacant homes in FL

    Bookmark   February 24, 2014 at 8:36PM
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That's the link I alluded to and provided to the OP... I think you're right that it's a real help.

    Bookmark   February 24, 2014 at 8:42PM
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I could not put my fingers on the full study, but that summary is probably good enough for most people.

    Bookmark   February 24, 2014 at 9:42PM
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