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I live nearish Pittsburgh. Our summers can get pretty hot and humid and our winters can get pretty cold. We have been planning to get a whole house humidifier because the house gets really dry in the winter. Recently, I watched a video about a whole house dehumidifier and it sounded like something we could use. We find ourselves running the AC too much in the summer just to handled the humidity.

I started reading about how to make this work with our thermostat (ecobee 4). It supports either a humidifier OR a dehumidifier, not both. This lead me to the question of what I was doing overkill or unnecessary?

Am I off base for wanting both? Or do I need to find a special thermostat?

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  • I have no real idea what I am talking about, but is LPG/natural gas heating an option for you? I posit that this will cost a similar amount to aircon to run, but will humidify the air in winter (as a byproduct - in NZ Gas heating is a problem BECAUSE it creates humidity) It also assumes that your power is coming from unclean sources or you dont care to much about the environmnent.
    – davidgo
    Commented Mar 24, 2019 at 5:19
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    Likewise, have.you crunched the numbers on aircon vs dehumidifier? A dehumidifier is basically an aircon which cools the air so water condenses.on the one side, then heats it back on the other side, slightly heating the environment in the process because dry air is easier to heat then wet air is to cool. So I posit that an aircon (in summer) gives you "free" / near free cooling if used.for dehumidifying.
    – davidgo
    Commented Mar 24, 2019 at 5:21
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    Monk would approve
    – Harper - Reinstate Monica
    Commented Mar 24, 2019 at 7:17
  • As long as they are both on high at the same time you shouldn’t notice anything p
    – Kris
    Commented Mar 24, 2019 at 23:02

3 Answers 3

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The problem is that your air conditioner is probably over sized or the fan speed is set too high. An air conditioners primary function is to remove moisture from the air. To big of an air conditioner and it drops the temperature too fast and can't pull down the relative humidity. If the fan speed is too high then the interior coil doesn't get cool enough to cause water to condense and drip into the drain. There are a few ways to make the air conditioner do its primary job of humidity removal work better. The simplest is lowering the fan speed. This link explains some tactics with a little detail. Air conditioning is tricky and it requires many measurements with specialized tools. It's not really a DIYer job but, with enough acquired knowledge anyone can understand it. Lots of installers and service techs don't actually know what they are doing. They often set the fan to the highest available speed, install the largest equipment possible, charge the system with the beer can cold method and generally accept that if it's blowing cold air it's perfect. That is not the case. Get a good, reputable service tech over and explain the issue. You don't need a dehumidifier, you need to set up the one you have. A good tech will have your house cool and dry in no time.

I'm from Toronto, we get a dry -40°F to a very sticky 110°F. If we can get by without dehumidifiers here, you can in Pennsylvania.

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    I disagree with your first statement that an air conditioner primary function is to remove moisture! It's primary function is to remove heat, a by product of this is a reduction of moisture. swamp coolers actually increase the humidity and cool as a form of airconditioning
    – Ed Beal
    Commented Mar 24, 2019 at 16:11
  • @Ed Beal Yes true, it removes heat and even the moisture it removes is done by removing latent heat. In the end it's only pumping heat to the outside. In my extremely humid climate we tend to think of the air conditioner as a dehumidifier first but in reality it is still a heat pump. I often describe the process to customers from the moisture point of view. Swamp coolers are something I've learned about from this site but would never see one in the field except maybe at an amusement park.
    – Joe Fala
    Commented Mar 24, 2019 at 16:37
  • I have installed swamp coolers all but 1 we're in commercial buildings, they were popular in Ohio cheaper to purchase and run than Freon based systems in the 70's but not able to cool as well in my opinion.
    – Ed Beal
    Commented Mar 24, 2019 at 16:46
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Pgreen2--Let me give you the novice approach to your problem. I live in Butler, Pa. and here is what I do, and it works. @Joe Fala is pretty much spot on but here is what you can do as a home owner. To check the fan speed, go out and buy a thermometer, similar to a meat thermometer, that reads temps between about 30 to 180 degrees. I have 1 that reads 0 to 220. Carefully put a small hole in the horizontal duct above the furnace and A/C coil to measure the discharge air temp. and a hole in the return air drop duct to read the return air temp. With the A/C on for 15 minutes or more check the temperature difference. You want a 15-20 degree temp drop across the A/C coil. Staying closer to the 20 degree drop is preferred. If this is what you get then great. If this is not what you have then changes are in order. Also, I have a humidifier on the furnace for winter use and I run A big de-humidifier in the basement in the summer to help control the humidity. (my basement if finished and conditioned) My total sq footage is 4000 including the 1st floor (ranch) and the basement, 20 year old house. My A/C is 3 ton which works well but may be a tad too big. I am not supposed to recommend a specific brand de-humidifier but I bought it at the orange or blue store and it is rated at 70 pints per day. This works for me. Make sure that you have your whole system looked at by a reputible service company. Get references and do not opt for the cheapest company. A word of caution; LP and nat gas does not effect the humidity in the home unless you are using an open flame heater like those unvented kind. A dehunidifier will not replace an A/C system as some people propose.

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    My last home was 3k sq ft very well insulated and we had a 5ton and it was not large enough for the hot days, in Oregon , a much cooler climate, although I agree with humidifier and dehumidifier. A 3 ton on 4k sq ft being two big??? And the answer you say is spot on? Is totally wrong! AC is there to remove heat not moisture. But no down vote because I agree with the humidity part of your answer.
    – Ed Beal
    Commented Mar 24, 2019 at 16:35
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I lived in Ohio for a few years and I found in the winter we did need need to have a humidifier in the winter because of the extreme cold dry conditions but the humid summers we had a dehumidifier in the basement to keep the moisture down, we did not install a humidifier but used an old school trick of keeping a kettle of water on top of the wood stove something I still do today in the winter on my pellet stove, it actually saves $ because if you want a cup of tea or cocoa the water is already hot. I fill it when I use some but if not used it will last for a few days.

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