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Thermostat and humidity settings when away in coastal FL

Dave_61Dave_61 Member Posts: 269
Hello we have a condo in coastal FL that we use several times a year. I am most concerned about mold, not temperature. What should we set thermostat temp and humidity to when it is unoccupied?

We have an Ecobee Smart Si thermostat that allows us to use ac as dehumidifier. Essentially, if I understand it correctly, when the thermostat temp trips the ac, the thermostat will monitor the humidity. If the humidity is above our upper limit, it will run the ac to decrease the humidity and continue to run ac up to 5 degrees below our temp set point. So, if we had upper level of humidity set at 56%, and temp at 82, when temp reached 82, ac would run until humidity was below 55% or until temp got to 77.

Thank you



  • icesailoricesailor Member Posts: 7,265
    edited June 2014
    What I did/my opinion:

    Here's what I did for my place in Wellington, Florida.

    I installed a Honeywell HC 60-1000 humidistat and wired it in parallel with the thermostat. Which is a clock thermostat. When I left, I set the humidity at 55% and the thermostat on Override at 85 degrees. At 80 degrees in my place, the humidity is always in the low 50%. In the heat of the Summer, as long as the temperature is above 85 degrees, the AC doesn't run but it will run if the humidity goes over 55%, the AC comes on. I've never had any problems with mold or high AC bills. For a while, I had it wired so that if the inside temperature supercooled and went below 65 degrees, it would turn on the heat strips. They never came on. I now live here. What I surmised is how it has worked.

    From what I learned about heat transfer from living in the North, most that I have come in contact think that heat flows backwards. In New England, when it gets cold, the heat in the house flows to the cold or out through the wall. If you take down sheetrock in a heated house in Massachusetts, you will see signs of mold on the inside of the plywood. In Florida, you find the mold on the back side of the sheetrock because the hotter air outside with the high humidity, flows to the cooler inside. But according to "discussions" I've had, its the other way around. And so, that makes me wrong in suggesting that the floor is colder in a AC'ed room than the ceiling, which as I understand it, is hotter because hot air rises. So, therefore, the damp earth gives off moisture close to the ground, which passes through the wall system to the inside. Because dampness flows to dryness. I see lots of rot on wood frame on slab houses here with AC. The Dew point is really the critical number If you don't let the temperature and Dew Point coincide, you won't get condensation.

    You want it cool, but not too cool.

    That's MY opinion. Its worked for me.
  • Rich_49Rich_49 Member Posts: 2,541
    edited June 2014
    Read This

    check out the whole site , also go to building science corporation site . All who have commented here should read this

    And this ; perfect wall
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • icesailoricesailor Member Posts: 7,265
    Way Up North:

    One article mentioned that this was devised in Norway and Canada. It probably works just as well in Massachusetts in the winter.

    Which way does the heat flow in a house in a tropic climate like the Gulf South, Florida or the tropics?

    If you have a cooled structure in South Florida, and it is 100f degrees  outside and the AC is keeping the inside temperature at 78f degrees, which way does the heat flow?

    If the outside air at 100f degrees has 80% humidity, and the inside 78f degree air is 40% humidity, which way is the moisture flowing?

    If you have a house in New England, and it is heated in the winter, and all the trim that is exposed to an outside wall, and the wood trim shrinks, whuch way is the moisture flowing? Which way is the heat flowing? If you had wood trim in the same heated New England building, and the trim is on an inside wall, why doesn't the wood shrink?

    Why is it that it swells back to its original size in the summer?

    Why is it that in New England, the moisture mold forms on the inside of the outside sheathing? But in Florida, it forms on the back side of the wallboard?

    WHy is it that in a Florida house that is stucco'ed outside, that there will be more mold at the base of the wallboard wall in the inside than at the top?

    An inquiring mind is inquiring.

    I have always understood that heat flows to cold and dampness flows to dryness. Etc.
  • SpenceSpence Member Posts: 316
    Vapor Barrier

    These posts are an incredible perception. Vapor barriers have traditionally been installed on the warm side, as should be. Easy if you live in Canada, and easy if you live in Florida. So what happens in between, when there are two seasons to overcome?

    Vapor barriers retard moisture flow from warm to cold; never the other way around. This means if I live in the Midwest, for example, I have to change my VB to one side of the wall in winter and the opposite side in the summer. No wonder there is confusion!

    What we have learned (among other things) is incorporating an air space within the wall, to allow moisture to condense and fall to the lower quadrant of the wall. That is why you see tuned-in builders adding weep holes in stucco or brick (for example) to wick out the juice.
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