In my 2 floor apartment that I own, I have a problem with duct condensation in the utility room and in a sheetrock drop ceiling where the ducts go through on the lower floor. My tenants keep the AC thermostats at 70 which results in a dew point of 49 degrees in the conditioned space. In the utility room, the temperature is 68, the dewpoint is 54, and the duct temperature is 53. In the drop ceiling space, the temperature is 66 degrees, the dewpoint is 55 and the duct surface temperature is 54.

In addition to the problem of duct condensation, with the thermostat set at 70, I have one bedroom at 74 degrees and another at 76 degrees.

Any thoughts on fixing the condensation issue and the warmer bedrooms?

I thought I would add a dehumidifier to the utility room, which is connected to the drop ceiling space, and get the dewpoint below 50 degrees, which is below the duct temperature.

For the hot bedrooms, I thought I’d add additional ducts to those rooms or window AC units and ask the tenants to turn the main thermostat up.

Any ideas? Thanks

I don't know why anyone needs it that cold. My temperature is set at 78. If it wasn't for my wife, who is already complaining, it would be at 80 or higher.

What happens if you turn the thermostat up a few degrees?

It doesn't sound like the unit is able to keep up at that setting anyway.

What is the temperature in NJ?

I agree, 70 setpoint in the summer is a little extreme. And funny thing in the winter it is set to 76.

Conditioned air should have a lot less moisture to condensate, it makes me think you have some unconditioned outside air penetrating into the utility room or perhaps the dryer vent is not sealed tightly and allowing moist air into the room. So, seal it up, tighten up the dryer vent, and wrap the ducts in insulation and see if you still have a problem.

Thank you Mike, that is great input. I hadn't considered the dryer vent, but there's a long one running though that space. And I think your right on moist outside air getting in somewhere, considering the dewpoint is 49 degrees in the conditioned space and 54 degrees in the duct chase and utility room.

And nice ideas on the balancing. Closing vents a bit is an easy thing to try. And I wouldn't be surprised if I have some air leakage in the hot room. Makes me think, I should get a blower door test.

I would agree that balancing is going to help. I insulate everything that I can. If balancing it out with the vents doesn't help then insulation might be the next step.

Thanks Zero for the reminder on the thermal camera. I think that would help if I get up there with a camera and some spray foam. I have a Fluke IR thermometer that I use all the time. I see the fluke IR camera is $1500-$2000 vs $120 for the IR thermometer I have. I'd guess you'd think it's worth it, as you have one. I see Klein Tools has one for $280 that looks good. What do you think? Thanks!

My camera is nothing that extravagant. It is a FLIR C2. Small, hand held, recharges with a USB port. You can save pics and I believe video to cards.

Think I got mine for just over $300 as a factory refurbished unit because newer versions were released.

Also have a little IR thermometer. Point and click type thing for getting close temps. It is not as fun to use and probably would be more of a pain in trying to find air leaks.

With regards to the warmer bedrooms, do they have return ducts in them or close by? In my old place, which had the return air in the middle of the house, if we closed doors too long it drastically changed the temps in there. I put smaller returns in each bedroom of the new place to help with balancing.

If leaving the rooms open doesn't help maybe simply running the fan on the furnace will help. It will keep circulating the conditioned air throughout.

Thanks zero for the details on your camera. I might go with that. No the bedrooms don’t have returns other than the space at the bottom of the doors. Makes me think I should get smart on this stuff so I can know what pressures, airflows, delta Ts, I should be seeing. At this point I’m shooting in the dark.

Thanks Givans. Learning why and how to adjust blower speeds will be part of my getting smart on this.

Robert, the mini split route is interesting but I’m thinking it’s $6k per zone, plus I’d still need to do something with the bedrooms.

Amy, my town is under rent control, so I’m restricted on what I can do.

Jason, I was looking for that on my thermostat but guess I need to check the manual.

I’m on vacation now, but will give you an update once I’ve taken action. Thanks all!!

I didn't read all the responses but...

1) Having a single return rather than in each room can contribute to this. Not a perfect fix, but leaving bedroom doors open when not in use can help this...or you can remove each bedroom door, trim 1/2" off the bottom, and reinstall to help air flow throughout the house

2) Install "gates" in some of the ducts to throttle down the air flow in some areas and not others...you may also be able to do this with the registers

3) Insulate all ducts in crawlspaces, attics, or other unconditioned areas.

Thank you Hoosier,

The problem is the students want privacy, so they keep their doors closed and they wished there were no air gaps around the doors to prevent sound transmission, but I do know return air is essential for hvac performance.

I'm afraid the system may be oversized and the ducts undersized, so I'm not sure the dampers will work and the system may have bigger problems.

I'll let you know once I hopefully have something worked out. Thanks again!