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re: Condensation on Air Registers
Posted on 6/25/21 at 9:24 pm to bapple
Posted on 6/25/21 at 9:24 pm to bapple
Ok - can see from your photo the two registers are very close to the air handler/supply plenum, as the return air grill, is right behind them. You have short supply duct runs, and the ducts are not picking up much heat from the attic, blasting out cold air in the kitchen (I’m guessing the HVAC service included additional R-22 refrigerant), the metal grills are cold and the room’s air dew point temperature is higher than the temperature of the metal registers causing condensation on the grills. I suggest you raise the thermostat temperature to 74 for a couple days to see if condensation ceases when you raise the room temperature.
With high humidity in that area, It seems you do have significant air filtration (heat seeks cold, wet seeks dry) so sealing the lights, skylight, etc. even if it doesn’t solve the immediate problem will not be wasted effort. If need be have a blower door test conducted to determine areas and severity of air infiltration into the house - so you’ll know what areas to be sealed. About $300 for the test - I’m having a blower door and duct leakage test done on my house next week.
If humidity is indeed 60-70% in areas serviced by the 2003 unit you do have serious air infiltration, another issue with the 2003 HVAC or a combination of both. Your 2003 HVAC should be maintaining humidity near 50% in this heat with long HVAC run times, unless your HVAC is seriously oversized. Get a hygrometer to double check your humidity against your thermostat - posted a photo below of a cheap but good one that’s pretty accurate and can be calibrated - I have 3 of them.
Lastly I’m posting a good article to help you understand and further troubleshoot your problem. Why Do AC Vents Sweat
With high humidity in that area, It seems you do have significant air filtration (heat seeks cold, wet seeks dry) so sealing the lights, skylight, etc. even if it doesn’t solve the immediate problem will not be wasted effort. If need be have a blower door test conducted to determine areas and severity of air infiltration into the house - so you’ll know what areas to be sealed. About $300 for the test - I’m having a blower door and duct leakage test done on my house next week.
If humidity is indeed 60-70% in areas serviced by the 2003 unit you do have serious air infiltration, another issue with the 2003 HVAC or a combination of both. Your 2003 HVAC should be maintaining humidity near 50% in this heat with long HVAC run times, unless your HVAC is seriously oversized. Get a hygrometer to double check your humidity against your thermostat - posted a photo below of a cheap but good one that’s pretty accurate and can be calibrated - I have 3 of them.
Lastly I’m posting a good article to help you understand and further troubleshoot your problem. Why Do AC Vents Sweat
1
Posted on 6/26/21 at 8:21 am to CrawDude
Man, this is some excellent information! Thanks for taking the time to write it up. 
You’re correct that the air plenum runs perpendicular to the skylight and the two registers that sweat are very short runs. My HVAC tech was actually surprised there’s a return air in the kitchen. We changed the filter which was covered in cooking oil and has only been installed for a month. Which leads to our next plan...
The wife and I had already planned on installing a vent hood in the fall since this kitchen has no way of venting cooking vapors. The cooktop is on the island (directly below the skylight) and it gets very steamy when we are cooking.
So step 1 will be to close up the massive hole where the skylight is. I’ll remove the framing, stick a section of drywall in there, and then float the drywall in place. That should give a good seal where the skylight is now. If the problem persists, I’ll get those Tenmat covers for the can lights.
I may still buy that humidity monitor for accuracy but since I already plan on plugging the skylight I think that’s first priority. I bet it reduces temperature in the room considerably too - the drywall in there measures about 120-130 degrees with an infrared thermometer on a hot day. It’s just pouring into the kitchen! That’ll be the first step.
Will report back.
You’re correct that the air plenum runs perpendicular to the skylight and the two registers that sweat are very short runs. My HVAC tech was actually surprised there’s a return air in the kitchen. We changed the filter which was covered in cooking oil and has only been installed for a month. Which leads to our next plan...
The wife and I had already planned on installing a vent hood in the fall since this kitchen has no way of venting cooking vapors. The cooktop is on the island (directly below the skylight) and it gets very steamy when we are cooking.
So step 1 will be to close up the massive hole where the skylight is. I’ll remove the framing, stick a section of drywall in there, and then float the drywall in place. That should give a good seal where the skylight is now. If the problem persists, I’ll get those Tenmat covers for the can lights.
I may still buy that humidity monitor for accuracy but since I already plan on plugging the skylight I think that’s first priority. I bet it reduces temperature in the room considerably too - the drywall in there measures about 120-130 degrees with an infrared thermometer on a hot day. It’s just pouring into the kitchen! That’ll be the first step.
Will report back.
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