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Started By
Message
Condensation on Air Registers
Posted on 6/25/21 at 7:31 am
Posted on 6/25/21 at 7:31 am
I got my AC serviced recently and the old 2003 unit is running great and blowing ice cold air.
The problem is that the previous owners probably didn’t service this unit for years and now it’s blowing colder... which leads to the next problem - condensation.
The two vents closest to the plenum are sweating and I think the issue is humidity leaking in from the attic. They installed 6 can lights at some point right around the two problem registers and I know they can let bad air in from the attic. Plus they have a really old skylight that is uninsulated and gets insanely hot during the day. I’m sure that area of drywall is letting in a lot of unconditioned air as well.
My plan is to demo the skylight area (not touching the roof right now though) and put fresh drywall on my ceiling, then float, paint, etc. I also will get some of those Tenmat covers for the can lights to air seal.
I ran a dehumidifier to see if the humidity being high in the room is causing the sweating. Low and behold, the issue goes away with that. So I figure sealing off air leaks will at least be the first step to fixing the problem.
Thoughts?
The problem is that the previous owners probably didn’t service this unit for years and now it’s blowing colder... which leads to the next problem - condensation.
The two vents closest to the plenum are sweating and I think the issue is humidity leaking in from the attic. They installed 6 can lights at some point right around the two problem registers and I know they can let bad air in from the attic. Plus they have a really old skylight that is uninsulated and gets insanely hot during the day. I’m sure that area of drywall is letting in a lot of unconditioned air as well.
My plan is to demo the skylight area (not touching the roof right now though) and put fresh drywall on my ceiling, then float, paint, etc. I also will get some of those Tenmat covers for the can lights to air seal.
I ran a dehumidifier to see if the humidity being high in the room is causing the sweating. Low and behold, the issue goes away with that. So I figure sealing off air leaks will at least be the first step to fixing the problem.
Thoughts?
4
Posted on 6/25/21 at 8:54 am to bapple
Insulate the boots where the resisters are and the duct work. Many hvac people don’t do a very good job insulating ductwork. That will cause the biggest problem with condensation like you described. Also any penetrations insulate seal them up tight vent the attic space as best you can.
This post was edited on 6/25/21 at 8:57 am
Posted on 6/25/21 at 9:24 am to bapple
Sounds as though you have identified the potential source(s) of the problem, and the steps to correct it. Cracker also offers good suggestions on the boots and ducts. Also check for potential leaks in the return air ducts/plenum (under negative pressure) that could be pulling in hot, humid air from the attic into the air handler. Are the sweating registers closest to the air handler/supply plenum, i.e., shortest duct run?
What do you set your thermostat at? The colder the house, the higher the probably of warm, humid air that enters the house from whatever source reaching dew point and condensing on the cold registers. If you keep the house cold, you can can temporarily raise the temperature to 74 or 75 F to see if that corrects the problem.
You monitoring your house humidity? A properly sized, tuned and operating HVAC should be able to maintain a relative humidity of 50% or lower during long run times of summer.
What do you set your thermostat at? The colder the house, the higher the probably of warm, humid air that enters the house from whatever source reaching dew point and condensing on the cold registers. If you keep the house cold, you can can temporarily raise the temperature to 74 or 75 F to see if that corrects the problem.
You monitoring your house humidity? A properly sized, tuned and operating HVAC should be able to maintain a relative humidity of 50% or lower during long run times of summer.
This post was edited on 6/25/21 at 9:42 am
Posted on 6/25/21 at 10:19 am to bapple
Insulated duct work and around box.
Posted on 6/25/21 at 1:52 pm to CrawDude
I appreciate the suggestions for insulating the registers. Unfortunately I already tried that and put quite a bit of the yellow batt insulation around them. I even insulated around the nearby can lights (using LEDs so no risk of overheating) and they still sweat.
Yes, only the two registers closest to the plenum are sweating. All the other registers are fine.
I have two units and this one is on my kitchen/living side. I keep it about 71 during the day and 73 at night while we sleep. I like my bedroom a good bit colder but that's for the other unit.
I haven't been but I notice on the thermostats, my bedroom side (the newer 2012 unit) can keep it around 49%-55% humidity. The kitchen one (2003 R22 unit) can only maintain the humidity between 60%-70%. So I think the massive air leaks in the kitchen are contributing to the sweating.
When I run my dehumidifier it reduces the amount of condensation on the registers and sometimes get rid of it entirely.
Here's a picture of my ceiling. There are a lot air entry points so I think I just need to start sealing stuff up.
[/img]
quote:
Are the sweating registers closest to the air handler/supply plenum, i.e., shortest duct run?
Yes, only the two registers closest to the plenum are sweating. All the other registers are fine.
quote:
What do you set your thermostat at?
I have two units and this one is on my kitchen/living side. I keep it about 71 during the day and 73 at night while we sleep. I like my bedroom a good bit colder but that's for the other unit.
quote:
You monitoring your house humidity?
I haven't been but I notice on the thermostats, my bedroom side (the newer 2012 unit) can keep it around 49%-55% humidity. The kitchen one (2003 R22 unit) can only maintain the humidity between 60%-70%. So I think the massive air leaks in the kitchen are contributing to the sweating.
When I run my dehumidifier it reduces the amount of condensation on the registers and sometimes get rid of it entirely.
Here's a picture of my ceiling. There are a lot air entry points so I think I just need to start sealing stuff up.
[/img]Posted on 6/25/21 at 2:26 pm to bapple
Your leaking hot moist air which is condensing at the vents.
Insulate and seal around cans and vents.
I had the same issue on a few spots - used a can of spray foam around all my lights and vents, then had guys come in to top off blown in insulation - no more condensation.
Insulate and seal around cans and vents.
I had the same issue on a few spots - used a can of spray foam around all my lights and vents, then had guys come in to top off blown in insulation - no more condensation.
Posted on 6/25/21 at 4:23 pm to eng08
I plan on doing that plus getting rid of the skylight. Highly doubt it’s airtight either.
Posted on 6/25/21 at 5:52 pm to bapple
Make sure all of your registers are 100% open, as this can also cause condensation issues.
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
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.
Posted on 6/26/21 at 11:01 pm to bapple
If your A/C filter is too restrictive (too high a rating), it will cause the vents to sweat. I use the lowest rated pleated filter.
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