I live in Florida, so I'm not really concerned at all about the coolness of the home in the winter. However, I'd obviously like to save as much energy as possible while gone for the day during the Spring/Summer by setting out Nest thermostat to the maximum safe temperature while away at work -- unfortunately, I'm having a hard time finding what this is.

I say safe because Florida is notoriously humid - I want to save money, but not at the expense of harboring mold behind the walls or something.

  • So you're really just thinking of running the A/C to limit humidity, and using temperature as a surrogate for humidity? I'm not sure that would work. If you set the threshold to 85F, and you had 2 weeks of 70F and rain, the A/C might never run but the mold would bloom! Can you convince the Nest to run 30 minutes a day regardless? – Harper - Reinstate Monica Feb 7 '17 at 3:13
  • Actually this would only be while I'm away at work - so maybe 10-12 hours a day most days. – ctote Feb 7 '17 at 3:44
  • Basically, I'd like to set it at like 90+ during the summer months while I'm gone to work, and have it start cooling off an hour or so before I come home (it's much cooler in the evenings so the performance of cooling I think would be much better than a constant lower temperature through the afternoon) – ctote Feb 7 '17 at 3:46
  • EcoBee has this as well: ecobee.com/2015/05/feature-friday-ac-overcool. It can also use a ventilator (eg whole house fan) to cool the house, depending on outside temperatures, which may also help. (No affiliation, just satisfied customer). – gregmac Feb 7 '17 at 16:44

I think you're asking a question that's analogous to "how do I measure the length of these pieces of wood, which have varying widths and densities, using these kitchen scales". Length and mass are related, but they're not the same thing.

You've asked about managing relative humidity by using measurements of temperature.

Don't. Temperature and relative humidity are related, but they're not the same thing.

Manage relative humidity by using measurements of relative humidity. Use your dehumidifier, heating and cooling, to keep the relative humidity below 70% or so. And when the property is occupied, keep it in the range 45-55%. That will be the most comfortable and healthy range, minimising the hazards from dry irritable air, dust mites, mould, and so on.

If you find particular spots that are susceptible to mould (these will be spots that are colder than the rest of the property), put the relative-humidity sensors there - you need to keep these spots well below 80% relative humidity: 80% is where you start to run the risk of condensation, and thus mould.

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