HellBill » Bills Categories: » Electric Bill » What temp should the thermostat be set at?

  #1 ()
: I have a vacation townhouse in Tampa FL... what temp should the AC be set at for when no one is there? I am trying to make sure I don't get any mold or mildew.

I've had it set to 81 degrees for the past few months... but I have no idea if that is a good number or not.
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  #2 ()
: I use 90F in arizona BUT we do not have humidity there. If your electric bills are high at 80F I would consider buying a dehumidifier---one that drains to a sink or floor drain etc----and go with a high temp to same money.
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  #3 ()
: The temperature itself is not enough to determine whether you'll have problems--it also has to do with other characteristics of your home.

When most people think about air conditioning systems, they think about the idea of cooling the space to make it comfortable, but modern systems also act to dehumidify the space as well. As warm, moisture-laden air passes over the coils, the heat is picked up and expelled, but the process of cooling also causes moisture to condense and drip from the coils. This moisture then collects within the unit and is expelled through a condensate drain. Consequently, when we feel air coming out of the unit, it feels comfortable to us because it is both cool AND low in humidity.

As your'e probably aware, high humidity levels can feel aweful even if temperature is relatively low, and in fact, higher temperatures can feel just fine if humidity is kept very low. The human body senses both of these conditions, and so most home air conditioning systems are designed to keep a healthy balance.

If you own a home that is particularly energy efficient, and you don't normally keep the temperature down very low, it may be possible that the system doesn't turn on that frequently. Consequently, the air inside the home can quickly turn musty and uncomfortable, even when the temperature is within a normally comfortable range. This is particularly true if the home is not very air tight, since it may allow moisture to enter a lot more quickly than heat.

On the other end of the spectrum, you could own a home that is air tight but has poor insulation, and as a result, even if temperature does not remain low, the existing air conditioning system is easily able to remove most humidity without it reentering through walls and floors. In such cases, a thermostat setting of 80 or more might actually feel very comfortable and result in low humidity.

In summary, humidity is a function of both how low your thermostat is set AND how quickly moisture is able to enter back into your home once it is removed. Additionally, the rate at which humidity is eliminated is proportional to how often your system cycles on, which is proportional to the difference between inside and outside temperature. As a result, you can't pick an arbitrary number on the dial and assume that it will be sufficient (or insufficient) for your home. At this point, it's all about your experience with your home. If you find that your home stays comfortable and low in humidity at 81 degrees, there's nothing wrong wtih keeping it there. On the other hand, if it requires a thermostat setting of 75 degrees to get the same result, then follow your experience and keep it there.

As a general rule, heat finds its way back into the home a lot quicker than humidity finds its way in, so in most cases, it's usually okay to let the temperature get a few degrees higher in an unoccupied home as compared to the normal comfortable temperature you set when you're home. In such a case, the system will still cycle on and off enough to remove humidity, but you'll waste less energy since heat transfer through your wall is directly proportional to the temperature difference between your inside temperature and the temperature outside. By minimizing this difference--that is, keeping your inside temperature a little warmer when it's hot outside--your system will turn on less frequently (though it will be frequently enough to eliminate moisture).
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  #4 ()
: 81 is kind of musty and hot. I would go with 78, it can keep things cool enough for things not to "sweat" or get musty and sticky, that's when you get problems. I work for a fire/water restoration company and some lady had her temp set at 81 and caused sweating in her home to where we had to go clean the home of the musty smell. It smelled really bad like sweaty socks. Its your townhouse, so do what your gut tells you.

How much you rent it for? I might be interested.
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