How to Diagnose and Repair a Humid Air Conditioner | Ask This Old House
Ask This Old House plumbing and heating expert Richard Trethewey travels to Orlando to diagnose and repair an HVAC system that is creating way too much humidity
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Time: 3-4 hours
Skill Level: Expert
Steps:
1. When diagnosing a humid air conditioning system, Richard usually follows a series of steps based on the most common issue and works his way to more specific issues.
2. First, Richard checks the sizing of the equipment. Square footage alone isn’t enough to determine the appropriate size of a unit, since insulation, building materials, window openings, etc., can all also impact how much work a unit will need to do. He’s often found that units are oversized with the thought that “bigger is better”, but when that happens, the unit won’t stay on long enough to eliminate humidity. If the unit is the wrong size, it will need to be replaced.
3. The next thing Richard normally checks is thermostat setbacks. If the setback temperatures are too far apart during the day, the air conditioning system will have to work too hard to eliminate heat and humidity in the building, which would explain why the house feels humid. Keep setback temperatures to around 5 degrees difference to prevent the system from overworking.
4. If neither of these issues is causing the problem, it’s time to start digging into the specifics of the system. In this case, Richard found that a UV light was requiring a fan to be on all day. That fan was pushing the moisture collecting on the cold coil of the AC unit back into the building, causing the humidity.
5. To solve this issue, Richard removed the UV light and adjusted the fan so that it only turns on while the unit is in cooling mode.
Resources:
Richard installed the Healthy Climate Solutions MERV 16 air filter [https://amzn.to/2wfqX9k], manufactured by Lennox (https://www.lennox.com/).
Expert assistance with this project was provided by 4 Seasons Air Conditioning & Heating (https://www.4acnow.com/) and by Air Conditioning Contractors of Central Florida (https://www.accacf.com/).
About Ask This Old House TV:
Homeowners have a virtual truckload of questions for us on smaller projects, and we’re ready to answer. Ask This Old House solves the steady stream of home improvement problems faced by our viewers—and we make house calls! Ask This Old House features some familiar faces from This Old House, including Kevin O’Connor, general contractor Tom Silva, plumbing and heating expert Richard Trethewey, and landscape contractor Roger Cook.
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How to Diagnose and Repair a Humid Air Conditioner | Ask This Old House
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Thank you!!!
First
How can I get one of you out to help me
this part is boring
That filter was thick.
How did the temp on the thermostat go from 73 to 78 so fast?
Good information
Richard did not go up in the attic. he would be sweating like a pregnant nun
No insulation? SMH That woman's electricity bill must be big.
Is that the only place that filter could be installed? I know I would not be well if I had to climb up into the attic to change the filter, even if it is only once a year. Couldn't it be installed on the return vent on the wall, in the house for easier access?
Clearly this problem has existed since installation. Why didn't she get it addressed by original installer earlier?
Karra needs to call in an insulation service. She's likely spending way, way more on cooling than she needs to.
Why did the audio quality get so bad on TOH videos? All the videos posted in the last three weeks have a bit rate of like 2.
Great show! Im wondering which app is used to calculate the decision on tonnage of AC? Thanks in advance!
Man the comments on these videos are disgusting. What is wrong with you people.
This was a really good segment! Thank you! Just goes to show to solve some problems you need experience and think very methodically.
Man, this 32kbit/sec audio you guys are pumping out lately in your videos is killing me.
Her hair is super nice.
The audio is a little different lately
Why does the audio sound off
Or sound bit deeper
If you wire the UV outlet off of the EAC terminal on the air handler board it will only turn on if blower is energized. That's what I do if the UV light makes ozone also
Wow, great info! I had no idea constantly running the fan would increase humidity. Our's is a little high and I’m running a dehumidifier to drop it.
The lady is very pretty.
Did I just watch
Audio is still terrible
mold mold mold mold mold
The uv light is used for one reason.
Mold!
Are u suprised yet. People get a uv light when mold is present. In the air or in the home.
Trees should never be included in a load calculation. They could be gone tomorrow.
Your smart… U made me smart with plumbing
Still audio problems
Ugh this video sucked
I think it’s safe to say this woman didn’t care about anything Richard was saying
6:03 if they're that worried about allergens, they should have some better way of preventing air bypass. Gaskets, weatherstripping, or whatever.
And maybe still use the 1 inch pleated filters to protect that giant expensive thing!
no insulation but at least her house is made of blocks am i right Europe?!? eh eh?
What’s up with the sound?
In spring and summer I have higher humidity than I like in the house. Several years ago I replaced my old Trane with what the dealer recommended – a very high-efficiency unit (even thought the old unit was very efficient and gave us no humidity problems whatsoever for almost 20 years and ran like a champ. But a freak problem NOT within the Trane unit forced us to scrap it (sadly) because the coolant needed was no longer available. So we were forced to buy a whole new system in order to comply with the new regs. Ouch! The new unit cools like gangbusters but it does it so fast there is not enough time to dehumidify the house like before. Have to have napkins under your glass of ice tea or whatever to soak up the condensation. Never had to do that before. I complained several times to the dealer/installer but to no avail.
I love how Richards narration during the HVAC upgrade clearly he watches a lot of How It's Made XD
We recently set up our Nest to run the fan for 15 minutes each hour between 12pm-10pm. I don't think it increases the humidity at all.
Interesting
Another larger than life blimp woman.
you couldnt put that downstairs so she could change it herself??? how is she supposed to get up there??? she is gonna have to pay to change that filter. sad. and what about old houses that leak air like a sieve? a constant fan keeps the temp constant, so what about their humidity??? good otherwise.
That's great you should make more HVAC videos so we can save on some energy, thank you!
I always assumed a 2 story house should leave the fan on all the time to help stop hot spots in the home. I've never had an issue with too much humidity. I'm kind of surprised he's saying that is one of the primary causes.
Why is he not putting it in? but yet he had a different technician
y no mastic
Awesome video some really helpful stuff
Wow that thing was big I wonder if it works the fan harder
I have an air conditioner which has a cooling function, heating function, and …….drumroll…..a dehumidifying setting. This dumb bimbo has too much money – no insulation, don't know how to use the dehumidify setting on the aircon, buys a dehumidifier, wants the house at 73/22 degrees in summer. WTF – 25 degrees is plenty cool enough and saves a shitload of electricity.
so should you run the fan on all day? Or should it only turn on when the AC turns on?
Going from a 1inch filter to a 4inch filter , wouldn't that causes significant air flow reduction? Isn't the evaporator fan motor designed for that one inch filter?
The AC coil is not cold when it is not running , so it wouldn't pick up humidity off the coil just running In fan mode. She's pulling in alot off outside air because off the lack off insulation. Might as well run the fan with the window open.
On that next thermostat there is an option for cool to dry. And it monitors the humidity level and turns on the ac if it is too humid.
Too much talking….
Hi, I mistakenly removed the styrofoam inside an 18000 btu air conditioner because I thought it was packing. Can this be repaired? Where do I buy the polystyrene styrofoam to repair this????
I don't think she expected such a HVAC Lesson! She's like umm-ok mmmm-hmmmm, Right! Ok, Yeah! I think she is over it and just wants to get it fixed! Lol!
should have put it downstairs where she can get to it. that is 75.00 just to have someone come and change that filter, if not more.
Did he say 3 tons on a 900sqft home?!??
I see obesity
The filters thickness being a 1 inch or a 5 inch is completely irrelevant to it's ability to filter larger or smaller sized particulates.The only point is that it's going from a merv 8 to a merv 16
Oh. My. Gosh. All this time and I thought running the fan at all times would help, but I have this exact issue.
Richard rocks! Life changing.
I had the same thing happen with my system when I ran the fan continuously. I disagree with Richard regarding the UV light, particular in the age of Covid. I am undergoing chemotherapy, and I have UV lights on my 2 systems in my house. While the light won't do anything against allergens, they certainly are effective against viruses, bacteria and mold spores. Plus, you can now get UV lights that don't generate ozone. These are relatively inexpensive insurance, and provide peace of mind. Obviously, they need to be maintained but so do the filters on the system.
The Filter which is MERV16 will not let a much air flow which means it will take longer to cool which means there will be more humidity removed when the A/C is operating.
Have no idea what he did to make the house “less” humid. All he said was he changed the settings on the thermostat but didn’t say what he set it to.
Something else that needs to be mentioned, is that the fan speed setting for the evaporator needs to be set at 400 CFM per ton of A/C. In this case, 1200 CFM. If the inside unit fan speed is set too high, there will be no way for the A/C unit to effectively remove the humidity in the house air. The inside evaporator in the basement will cool, but not dry the air if the airflow is too high, resulting in a cool, but very damp home.
Very well diagnosed.