HVAC Register Condensation; Condensation on exterior of attic unit

Morgan

3 years ago

last modified: 3 years ago

First time poster - I've been chasing an issue over the last month or two in my home. House details:

- 1749sq ft

- single story

- built in 2017

- crawlspace (unconditioned)

- ac unit in attic

- located in central Virginia

The first thing I noticed was condensation on the register in the master bath. This vent is closest to the AC unit upstairs. I removed the register and did not feel any condensation in the ducting. I did notice that the mastic around the boot wasn't attached to the drywall very well, so I picked up some Hardcast 1402 mastic tape to seal the gap (per suggestions in another thread). This did not fix the issue.

I picked up a humidity gauge, and with the AC set to 71 around the clock, I'm seeing around 56-58% humidity in the house. The set point in the unit is 40-45%, so it's clearly having difficulty pulling moisture from the air.

I went into the attic and did not see any condensation on the ductwork, but it is insulated, so it's hard to tell. The boot was completely covered with blown in insulation as well. However, I did notice that the AC unit itself was sweating, with the drain pipe being the worst.

Under the unit:

Drain sweating quite a bit:

That's a fresh puddle directly below this section of the drain. I think that may be mold spores on the piping as well:

Sidenote - Is the drain pipe supposed to have a trap in it?

After reading this thread , it looked like the authors AC unit was oversized and was short cycling. I'm not sure if I'm experiencing a similar issue. I plan on calling the company that installed the HVAC system Monday along with the builder to describe the issue and see what their suggestions may be, but is there anything I need to look for?

Potentially related(?) - I noticed condensation in the dryer lint trap this morning. I moved the dryer out of the way and saw condensation inside the vent ducting as well. The duct is 21 feet long (if the plaque is to be believed), and runs down into the crawlspace and out near the foundation. Glancing in the crawlspace, I don't see any standing water, but I did not do a thorough inspection. I'm heading to one of the big-box stores today to grab a dryer duct cleaner to see if there's a blockage there.

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Comments (5)

Morgan
Original Author
3 years ago
Update - no blockage in the dryer duct. The humidity dropped as low as 53% yesterday evening but is currently sitting around 60% during the day - which is peculiar as I always thought humidity in a house tends to rise at night.
mike_home
3 years ago
Do you think the AC is short cycling? How long does it run when the thermostat cools for cooling? Do you want the house to be 71 degrees or you trying to see if you can reduce the humidity? Most people are comfortable at 75 degrees and 50% humidity. Do you find the house to be uncomfortable?

What is the humidity level in the unconditioned crawl space? Is the ceiling above the crawl space sealed. The crawlspace may be a big source of the high humidity problem.
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Morgan
Original Author
3 years ago
last modified: 3 years ago
@mike_home According to the device logs, the AC is running for 6-10 minutes at a time. I'm not sure if that's considered short cycling. I had set the thermostat to 71* in an attempt to reduce humidity. Previously, it would be set between 73 and 75, but the humidity would make the house feel hotter than the temperature made it seem.

I can put a probe into the crawlspace to get a better idea on what the humidity levels are. When you ask about the ceiling above the crawlspace, what do you mean? When I look under there I see what I think is a vapor barrier on the ground, and then the joists and insulation are open - nothing covering them.
mike_home
3 years ago
The ceiling above the crawlspace is the bottom of the first floor. The warm moist air in the crawl space will rise up into to house if there is no vapor barrier to stop it. I would expect a three year old house to have tight windows and doors. The crawl space might be a source of the excess moisture in the house.

What size is the AC? I would think a 2.5 ton single stage, or 3 ton 2-stage AC would be sufficient for a newly constructed 1749 sq. foot single story house. Did the builder provide a load calculation? A 6-10 minute run time might be considered short cycling. How often does this happen in an hour and what is the outside temperature?
Morgan
Original Author
3 years ago
last modified: 3 years ago
@mike_home I believe it's a 3 ton unit, but I will verify this afternoon.

I don't believe the builder provided me with a load calculation. I bumped the temp up to 73 this morning as it was pretty cold in the house. Within the last hour (after the temp change), the AC ran for 19 minutes and then 31 minutes. It just kicked on again, 5 minutes after going idle. I've not really paid attention to how often it runs in the past, but that seems like a lot.

It's currently 88* outside and overcast, and approximately 77% humidity.

At 10am this morning, the humidity inside the house (according to the controller) was 55%. It's now 64%.

HVAC Register Condensation; Condensation on exterior of attic unit

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HVAC Register Condensation; Condensation on exterior of attic unit

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