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Troubleshooting bedroom humidity levels (continued from previous thread)

Posted on 5/18/23 at 5:41 am
Posted by StringedInstruments
Member since Oct 2013
18526 posts
Posted on 5/18/23 at 5:41 am
I posted about a week ago about my bedroom being uncomfortable

Before investing in a nest or ecobee thermostat system, I grabbed a few thermometers/hygrometers to place around the house to check the relative humidity at night. I learned that in my bedroom, even when the a/c pumps at a 69 setting, the temp will cool and remain stable but the RH is rising to 75% after around 20-30 minutes.

Granted it’s rained a good bit here in Birmingham the past few days, I still don’t like the mugginess of my bedroom at night, and I think it’s keeping me from sleeping.

My bedroom sits over the crawlspace entrance. I rebuilt the door myself with a thick layer of wood, and it’s a really snug fit into the entry way. I also glued a thick layer of foam insulation on the back to help with…insulation. A new crawl space vapor barrier was installed two years ago.

But I’m wondering what else I can do to fix this? I don’t think the new thermostats will work because the temp is getting low. It’s the humidity that is rising too quickly in my bedroom.

I assume new windows (there is one large double window frame plus a single) would help. I know the attic needs an update regarding insulation.

But should I also look into insulating the subfloors beneath my room? Or installing a whole house continuous dehumidifier in the crawlspace?

I don’t think there are any bedroom-sized dehumidifiers that will be quiet enough to use at night.

Thanks, gentlemen
This post was edited on 5/18/23 at 5:43 am
Posted by notsince98
KC, MO
Member since Oct 2012
18099 posts
Posted on 5/18/23 at 8:08 am to
to do this right you need a pro like a home energy expert. Someone that can come in and do blower door tests, duct leakage tests and IR camera testing and find out where the leaks are in the house. Otherwise, you will mostly just be guessing and throwing money at things hoping it works.

In the mean time, what CFM/ton setting are you using on your furnace/air handler? Or, what tonnage is your AC/heat pump and what CFM output is your blower set to? There may be an easy first attempt here that wont cost you any money.
This post was edited on 5/18/23 at 8:09 am
Posted by notsince98
KC, MO
Member since Oct 2012
18099 posts
Posted on 5/18/23 at 8:11 am to
Also, at night when your thermostat is set to 69F, what is the temperature at the t-stat and what is the temperature in your room?

One common issue of setting cooling temperatures so low (less than 70F especially) is that you get higher humidity levels. It is hard to cool moist air down that far and keep humidity low because as temperature drops, relative humidity goes up.
Posted by baldona
Florida
Member since Feb 2016
20597 posts
Posted on 5/18/23 at 12:24 pm to
quote:

I don’t think there are any bedroom-sized dehumidifiers that will be quiet enough to use at night.


These are super quiet actually, for a bedroom you just need a very small one.

When you say 69, that's at the thermostat right? You need to measure the temp in your room also.

For best humidity control you want your HVAC running almost constantly during the summer. This means its proper sized and running often pulls the most amount of moiusture.

Given that, as said already you also likely have a bad air leak situation from the crawlspace, windows, etc. that's letting in moist outside air.

If this is an older home many of them also have very poor return air vents or usually none at all. So you may be getting cold air vented IN but no air pulled OUT. So you just have cold wet air in your room. You need to have a space under your door or even better return air vent to your unit for best results.

ETA: FWIW when most people say they like it cold to sleep they mean they like it low humidity. They turn the air colder to remove humidity, but the cold air is just a secondary benefit.
This post was edited on 5/18/23 at 12:26 pm
Posted by magicman534
The dirty dell
Member since May 2011
1588 posts
Posted on 5/18/23 at 1:41 pm to
Do you have a cathedral ceiling with a beam ?

Reason I ask is I had the same issue last year. Vents sweating, leaking on bed, high humidity, took forever to cool. The Sheetrock had a 1/4” gap between beam, 16’ long x 2 sides so every time the AC kicked on it was sucking hot air from my attic. Never noticed it bc it’s 15’ in the air. Sealed that up and now I freeze my tits off in there. Here’s a pic
Posted by Snow
Member since Nov 2016
74 posts
Posted on 5/18/23 at 8:11 pm to
I fought humidity issues for years and eventually figured out my blower speed was set too high. It’s not hard to adjust, but it will vary based on the system. My house went from 60% - 75% humidity to 45% - 60% year around.
Posted by Baers Foot
Louisiana Ragin' Cajuns
Member since Dec 2011
3547 posts
Posted on 5/18/23 at 10:20 pm to
Whoever your energy provider is likely offers free residential energy audits. I did one with LUS here in Laffy and a guy came with a FLIR tool and looked around my house for any leaks.

Try reaching out to your energy company, or you could even purchase a FLIR device that on Amazon that attaches to your iPhone ($300-$400 though).
Posted by Pezzo
Member since Aug 2020
1995 posts
Posted on 5/19/23 at 7:20 am to
it may only be a temporary fix, but a dehumidifier may be an option

is there any windows in the room?
This post was edited on 5/19/23 at 7:21 am
Posted by CrawDude
Baton Rouge
Member since Apr 2019
5291 posts
Posted on 5/19/23 at 2:09 pm to
You’ve gotten good advice and recommendations from notsince98 and others in this thread. I would have a blower test (energy audit) conducted to check and identify leakage.

You may have to reduce the air handler/furnace blower speed to get better dehumidification particularly if you have a furnace as furnaces are usually set at the factory to the highest speed which is near 400 CFM per ton. You probably need to set air flow at 350 CFM per ton, or 1400 CFM, in light of the fact you upsized the unit.

And you are measuring relative humidity within the room (mixed air) and not the humidity of cooled air exiting the floor vent - correct?
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