re: Brand new built home has high humidity. Normal?

What everyone has said about over sizing of the HVAC unit, short run time, in a well-insulated house is correct. But does the house feel humid inside or just the reading on the thermostat is high? And a new house could have higher humidity as building materials dry out.

I ask, b/c as I understand humidity readings on thermostats are often very inaccurate. Buy 1 or 2 these inexpensive humidity meters (Amazon) - they are accurate and can be calibrated. I have several and they are accurate. See how the humidity numbers with these compare with those of your thermostat.



Usually, HVAC blower motors (blower inside the furnace-air handler) are set at the highest run speed for cooling at the factory - that moves about 400 cubic feet per minute (cfm) of air per ton of AC. Many techs don’t change that with the install. But in humid regions it’s best to lower the speed to about 350 cfm per ton which will help with humidity removal (humid air in the house stays in contact with the cold evaporator coil for a longer time helping to lower humidity). That would be the easiest thing to look into first.

Also if you could provide tonnage of the HVAC, conditioned area, sq ft, of the house, and your HVAC running times between cycles in mid to late afternoon that would be helpful. At air temperatures of 85 F and higher you should be having fairly long run times between cooling cycles if system is properly sized.

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you probably have too big of an ac unit in a too good of insulated house. unit isn't running long enough to get to your cool down temps. may have to add a dehumidifier to your system.

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^^^this. Some folks want a bigger unit because they think it cools better and doesn't run near as much, but the info above can be an issue.

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House feels comfortable for the most part. I’m not sweating, just doesn’t feel as cold as I’d like. The 64% reading is coming from the thermostat app. Not sure how it knows but that’s where I’m getting the reading from.

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Understood - for me personally I can tell when relative humidity in my house exceeds 55% just by comfort-feel, but that is rare as my HVAC is properly sized and blower speed is set at 350 cfm per ton.

I’m not sure how humidity provided by the thermostat is determined or calculated, but I follow some professional HVAC sites (just an interest of mine), and they state they are often inaccurate, by a lot, and they are the guys that recommend the inexpensive Accurite humidity meter I provided in my earlier post as a cross check.

As another poster mentioned, what do you set your house thermostat temperature at? Lowering it a couple degrees, even temporarily, should reduce humidity from the longer HVAC run time - just a DYI diagnostic tool to help troubleshoot.

It could also be that the refrigerant level is a bit low from the install - units from pre-charged from the factory but often some additional refrigerant needs to be added if the line set is long run. You said it’s a new house, when did you move in? I ask b/c it is harder for a tech to get a an accurate reading on the HVAC pressures & diagnostics when it’s still cool outside, and sometimes HVAC techs need to come back out and re-check and adjust the refrigerant charge when it’s hot.

As you can see, it could several + things causing the issue, some easily fixed, others, like over-sizing, more problematic.

I’ve been running the fans too as well as lowering the temp to 68°.

The reading has gone from 65% to 60%

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I keep it between 70-72 during the day and 66 at night.

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good lord
you wouldn’t last a day at my house

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Anyone ever dealt with this?

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Everybody with an oversized conventional central AC system.

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I keep it between 70-72 during the day and 66 at night.

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You keep cold enough not to have humidity problem if the unit is properly sized and operating according to specs. It could be as simple leak in a return air duct work in the attic pulling hot humid air into the air handler/furnance. Just another potential possibility.

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Thursday of last week.

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OK, but that still doesn’t mean the refrigerant charge is set properly, would have to be verified by a tech.

I’d try to verify the high humidity in the house with another device as I suggested before having a HVAC tech come out for your one free call. I’d also request that a senior HVAC be sent out to look it over. It’s usually the young techs, some without much experience, that are sent out to do installs and the senior guys handle the more difficult service calls.

Ideally, once a HVAC is installed, it should commissioned - meaning a senior tech comes out measures everything verifies the unit is operating according the manufacturers standards, writes it down on a in commissioning report which is provided to the home owner. Sadly, very few companies do this.

we always commissioned but we charged for it. Usually a nominal fee but that’s why DSLD doesn’t do it

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one free adjustment.

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That’s to balance the system making sure airflow is proper to all rooms. Has nothing to do with humidity control. Mine stays right at 60% but I’d like it to be closer to 55%. I also don’t have a spray foam house. I have blown in insulation.

Is the fan set to auto? I accidentally switched mine to on for a couple of days and never realized it until house was starting to get damp. Switched back to auto and it cleared up in a few days