DIY Home Improvement Forum banner

1 - 20 of 20 Posts

·
Registered
Joined
·
101 Posts
Discussion Starter · #1 ·
We live near Houston TX. Our house was built in 2016. We moved in in 2019. Roughly 2150sqft. All the energy efficient stuff except radiant barrier. I had radiant barrier installed last summer and another 14 inches of insulation on attic floor.

The days around here have been 92-95 degrees. Our ac is a 3ton, which I though was kinda small but I was told it was sized appropriately for the home. It has a “fresh air dampener” that automatically opens when blower is running. It has no issues running and keeping the inside temp 71-72 all day long. But what I’ve started noticing is the humidity in the home being higher than what I remember in the past. It’s sticking around 62-67%. Then of course when the sun goes down it’ll pull down into low 50s.

I’ve checked all the doorways for leaks. Their actually double sealed. I’ve checked the poop vents in the bathrooms. All windows are double pane sealed up. Ac drains are clear.

Earlier today I installed an access panel to see if the coil was dirty. Looks brand new. Outside unit is clean. I’m getting a 18-19 degree drop across the evap coil.

So I don’t know at this point. Any ideas?
 

·
Registered
Joined
·
12,894 Posts
Not an expert on ac, I'm in the northern cold region, but I'll ask, why the fresh air intake? Relative humidity varies with temperature so bringing in hot humid air and cooling it down raises the RH for that air and the house.

Possibly review why you are pulling in fresh air and adjust as needed to balance the humidity.

Energy efficient homes can require fresh air, but the guidance isn't always a good fit for every home and climate.

Bud

Just another note, does your ac cycle on and off frequently or run for long intervals?
 

·
Registered
Joined
·
101 Posts
Discussion Starter · #3 ·
Not an expert on ac, I'm in the northern cold region, but I'll ask, why the fresh air intake? Relative humidity varies with temperature so bringing in hot humid air and cooling it down raises the RH for that air and the house.

Possibly review why you are pulling in fresh air and adjust as needed to balance the humidity.

Energy efficient homes can require fresh air, but the guidance isn't always a good fit for every home and climate.

Bud
When we first moved here I couldn’t figure out how the fresh air intake could benefit anything other than making the load on the EVAP coil bigger. We go in and out of our home to the backyard quite a bit, so there’s plenty of fresh air changes in my mind. But hey I’m no expert either.
 

·
Registered
Joined
·
12,894 Posts
I added another question to the above.
Being a newer home was there any energy related information provided ot left near the electrical panel or elsewhere?

There are calculations that guide how much fresh air is needed but like you said your activity may be providing most of that.

As a test you could shut off that intake and monitor the RH.

Bud
 

·
Registered
Joined
·
101 Posts
Discussion Starter · #5 ·
Not an expert on ac, I'm in the northern cold region, but I'll ask, why the fresh air intake? Relative humidity varies with temperature so bringing in hot humid air and cooling it down raises the RH for that air and the house.

Possibly review why you are pulling in fresh air and adjust as needed to balance the humidity.

Energy efficient homes can require fresh air, but the guidance isn't always a good fit for every home and climate.

Bud

Just another note, does your ac cycle on and off frequently or run for long intervals?
The AC will run constantly from about 4pm till around 9 or 10pm. I’m assuming that’s because by 4pm the house has absorbed the heat. other Time it does cycle but it’s not a short cycle.

also I forgot to add, I hate the way they installed the blower up in the attic. It’s literally on one end of the attic making some runs short and other over 30 or 40’. When it comes time to replace this thing we are moving it to the middle!!!

another thing I forgot is we have 5 air returns. One main one then one in each bedroom.
 

·
Registered
Joined
·
12,894 Posts
I'm turning in for the night and hopefully some of the pros will review your post.

Long runs are good as they remove more moisture.

See you tomorrow,
Bud
 

·
Registered
Joined
·
8,359 Posts
When it's humid outside, keeping the fresh air manually closed so help. It's designed to make sure that you have fresh air to breath and are pushing "polluted" air outside. (CO2 from your breathing, VOCs from building materials, etc) Overall, the fresh air is better for you and your house, but during very humid times it may be just a bit too much for your system. Having the fan on auto instead of continuous on will help, if you don't already have it set that way.

30-40ft runs aren't terrible, especially when insulated well or in conditioned space. It can be noticeable when in the attic and insulated as standard for your area. Each installation is different but if it's not causing you grief, it isn't a big deal. (I personally avoid ducting in the attic as much as possible, but I live in an area where fully conditioned basements are normal.)

Cheers!
 

·
Registered
Joined
·
101 Posts
Discussion Starter · #8 ·
So the fresh air dampener has 3 settings. I put it on the lowest one. So it barely opens. I stuck a temp probe in the fresh air duct and it’s pulling in 95 degree humid air from outside. while the rest of the returns are 73-74. We go in and out quite a bit so my thinking is, maybe during these really hot months, closing the fresh air dampener. Then during the cooler months, Plugging it back in.

Also one of the things I noticed today, we raised the thermostat to 74 instead of 70 during the day and humidity stayed around 59-60 instead of high 60s. Something about cooler air won’t carry moisture to the coil. Dew point, etc etc.

the reason I don’t like the super long runs is because. My air gets cooled to 54-55 degrees but
By the time it gets to the end of those long runs it gets up to 62-65 degrees. the shorter runs it stays around 55-56 at the register.
 

·
Registered
Joined
·
12,894 Posts
Those longer runs need more insulation, a lot more.

Bud
Some reading
 
  • Like
Reactions: supers05

·
Registered
Joined
·
8,359 Posts
You really should insulate your longer ductwork better. Even if that's literally applied over top of the existing Insulation.

Cooler air holds less absolute moisture then warmer air. This means that cooler air with the same amount of water in pounds than the warmer air, will have a higher relative humidity. AC's also struggle more at removing moisture the cooler the return air is.

Cheers!
 

·
Administrator
Joined
·
41,579 Posts
Here we put the fresh air damper on a control that only allows the damper to open for X minutes an hour.

Helps a lot to keep the humidity from rising too much in summer, and getting to low in winter.
 

·
Registered
Joined
·
101 Posts
Discussion Starter · #13 ·
Here we put the fresh air damper on a control that only allows the damper to open for X minutes an hour.

Helps a lot to keep the humidity from rising too much in summer, and getting to low in winter.
yea mine just opens whenever the blower is on. Maybe I should try just closing it for the summer.
 

·
Administrator
Joined
·
41,579 Posts
Try it for a week or so. If the house starts to feel stuffy, open it up maybe 5%.
 

·
Registered
Joined
·
101 Posts
Discussion Starter · #15 ·
It only has a 0-4 setting. So what I noticed is we raised the thermostat temp to 74 during the day vs 70 and humidity was about 10% lower. then at night we put it down to 72. Does that make sense?
 

·
Administrator
Joined
·
41,579 Posts
The higher the indoor temp, the more moisture it can hold, so RH will be lower.

Set it to lowest setting. If its already there, turn it off for the weekend and see how it feels Monday night.
 

·
Registered
Joined
·
101 Posts
Discussion Starter · #17 ·
The higher the indoor temp, the more moisture it can hold, so RH will be lower.

Set it to lowest setting. If its already there, turn it off for the weekend and see how it feels Monday night.
Higher indoor temp means more humidity gets Carried to coil to be dehumidified?
 

·
Registered
Joined
·
8,359 Posts
Higher indoor temp means more humidity gets Carried to coil to be dehumidified?
70°F at 60%rh has the exact same water in the air as 74°f at 68.6%rh. (0.01078 lb.water/lb.air)

Since the dew point is also the same,(59.2°f) the ac will be removing the same amount of moisture, for every min it runs.

Cheers!
 

·
Administrator
Joined
·
41,579 Posts
Higher indoor temp means more humidity gets Carried to coil to be dehumidified?
No. Just means the air can hold more.

Air at 70°F and 52% RH. When the air is warmed to 74°F with no moisture added or removed is now at 45.4% RH.

RH means the amount of moisture the air contains, compared to how much it can hold.
 
  • Like
Reactions: supers05

·
Registered
Joined
·
68 Posts
93 °F°C
Precipitation: 0%
Humidity: 47%
Wind: 9 mph
Houston, TX
Friday 4:00 PM

67 °F°C
Precipitation: 20%
Humidity: 93%
Wind: 8 mph
Northern Virginia
Friday 5:00 PM
Cloudy

So I don't know much about houson. If your gaining humidity it must come from somewhere. You said you have a ceiling fan sucking hot air out of the top floors (i assume that's what it's for, and that it's not running backward wired backwards).

You said you know the subcooling of your evap, so you know it's not icing over and thawing.

Jack: it's gotta come from somewhere. Your not telling us everything.

Now it's natural for eval coils to drip and drain, so that can't cause "high humidity". Some people even install hamster wheels to add humidity since the AC might removes "too much".
 
1 - 20 of 20 Posts
Top