Could this cause high humidity in my house?

2,351 Views | 12 Replies | Last: 4 yr ago by The Fife
rlb28
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AG
I googled "supply and return air temperature difference" because I think there is an issue. I'll go by The Home Depot on my way home to get a temperature probe. But... if the difference is less than 16 degrees could that make there be high humidity in my house?

Right now my Nest thermostat is set on 72, the outside temp is 75 and the inside humidity downstairs is 60% and upstairs is 61%.

From Google:

Low Delta T issues (less than 16F difference)

Low evaporator Delta T means that there's an excessively small difference between the incoming and outgoing temperature. Low evaporator Delta T problems include:
  • Low refrigerant (Freon) levels
  • Weak compressor valves
  • Leaking reverse valves
  • Leaking return air ductwork
Kenneth_2003
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AG
This probably isn't the best time of year to chase down humidity issues. Most likely the system just isn't running enough to get the humidity down. The last couple nights in Houston were back down in the 50s.

Next week we're supposed to start seeing days up in the 90's. That should have your system running a bit more.
TexAg1987
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Is it 72 in your house? Is the unit running?

It is probable that on high humidity days, when the outside temp is close to the indoor set point, the unit doesn't run long enough to dry the air before the set point is reached.

Easiest thing to do would be to set the temp lower a couple of degrees to get the air dried out then set it back to normal. Don't open doors or windows too much or you will let humidity back in.

You could do the opposite and run the heater for a few degrees then turn cooling back on.

Or get a dehumidifier.

If your unit cannot cool to 72, then you have other issues like you described.
rlb28
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AG
Kenneth_2003 said:

This probably isn't the best time of year to chase down humidity issues. Most likely the system just isn't running enough to get the humidity down. The last couple nights in Houston were back down in the 50s.

Next week we're supposed to start seeing days up in the 90's. That should have your system running a bit more.
I agree, but it's been an ongoing issue since last year. I've just been too lazy.
TexAg1987
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rlb28 said:

Kenneth_2003 said:

This probably isn't the best time of year to chase down humidity issues. Most likely the system just isn't running enough to get the humidity down. The last couple nights in Houston were back down in the 50s.

Next week we're supposed to start seeing days up in the 90's. That should have your system running a bit more.
I agree, but it's been an ongoing issue since last year. I've just been too lazy.
Does your system cool ok?

If it is cooling too efficiently, you can get the same symptoms. The fix would be to slow down your fan speed so that the air spends more time over the coils to draw out more moisture.
rlb28
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AG
TexAg1987 said:

rlb28 said:

Kenneth_2003 said:

This probably isn't the best time of year to chase down humidity issues. Most likely the system just isn't running enough to get the humidity down. The last couple nights in Houston were back down in the 50s.

Next week we're supposed to start seeing days up in the 90's. That should have your system running a bit more.
I agree, but it's been an ongoing issue since last year. I've just been too lazy.
Does your system cool ok?

If it is cooling too efficiently, you can get the same symptoms. The fix would be to slow down your fan speed so that the air spends more time over the coils to draw out more moisture.
I think it's cooling fine.

Of course, it's always hotter upstairs and the humidity level is higher. Right now Nest thermostat says humidity downstairs is 61% and upstairs is 68%.

Once I check the temp difference between return and vent I think I'll call in a claim to my home warranty.
evan_aggie
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AG
I had a 2nd humidistat+thermometer sensor that was always 5-8% lower than the Nest.


ABATTBQ11
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AG
What is your delta T? You need to take 3 measurements at different supply registers and one at your return with a temperature probe. Average the 3 supply measurements and subtract from the return to get your delta T.

Edit: Nvmd. I misread the OP a little. When is the last time you cleaned your coils?
buddybee
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Having years of experience in the HVAC business. I would do the following, 1) Have evaporator coils cleaned 2) Make sure you have an approx. 25 degree drop across the coils. Take tempt. at intake and vents for the drop. 3) If the humidity is too high have the fan speed slowed down and this result in more humidity being removed. 4) Make sure your system is balanced. A 50-60 % humidity is in the ball park. You do not want the humidity too dry. All of this can be done by a good HVAC tech. If he gives you that deer in the headlight look when you ask him about these items, find a new tech. Hope this helps.
EcoZapp.AC&Air.Purifiers
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No shout out for us yet :/


-figured we would have been mentioned as the cause of high humidity because of a video or something...
EcoZapp.AC&Air.Purifiers
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Best advice after being in the HVAC business for years now....

- stay away from those Home Warranty claims when it comes to HVAC or most companies that work for home warranty companies. Slim margin calls usually doesn't equal the best techs, or really even the average techs..

~$500 Home Warranties Policies 'usually ' don't offer much of anything when HVAC trucks/ Vans/ Techs take $$$$ just to turn on every morning.

Time Vs. Money Vs. Them not covering much tends to be a lose- lose

BrazosDog02
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AG
OP, before you do anything I'd make damn sure your measurements are right. im going to guess you have an oversized AC system. Builders and shoddy techs love this because man j is hard and people ***** and moan when their AC won't keep 77 degrees in the middle of August. Pro tip...it's not supposed to in this region. Anyway..... You can get a tech out to set the settings properly and make sure it's running and set up for the proper tonnage of the outdoor unit and air handler. Perhaps the installer left everything default. I have seen this multiple times Check that first.

Let's work our way up from obvious and cheap to complicated and expensive.
Whoop99
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AG
I had my roof replaced 2 years ago in March. The roofer installed new power vent fans. Last spring, while up in the attic, I noticed that the fans never had power run to them. After calling the roofer and having the vents wired up, the humidity in my house shot up and the AC ran all day for 2 days. Using the data collected by my ecobee thermostat, I eventually pieced together that the new vent fans were having trouble pulling enough air through the soffit vents, so they were pulling conditioned air from inside the house. I spent an hour working my way around the outside of the house pulling the vent covers off and hosing them clean. As soon as I did this, the humidity returned to normal and the AC stopped running constantly. Make sure your attic ventilation is working as it should.

Good luck!
Gig 'Em,

Whoop99
The Fife
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BrazosDog02 said:

OP, before you do anything I'd make damn sure your measurements are right. im going to guess you have an oversized AC system. Builders and shoddy techs love this because man j is hard and people ***** and moan when their AC won't keep 77 degrees in the middle of August. Pro tip...it's not supposed to in this region. Anyway..... You can get a tech out to set the settings properly and make sure it's running and set up for the proper tonnage of the outdoor unit and air handler. Perhaps the installer left everything default. I have seen this multiple times Check that first.

Let's work our way up from obvious and cheap to complicated and expensive.
This and the reply below are the two best ones in the entire thread.

If whoever installed the A/C sized it based only on the square footage of the house or some rule of thumb you're starting from behind and may end up needing to add a dehumidifier to the system. Don't know without knowing more detail.
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