Will Clogged Central Air Filter Cause Sweaty Ducts

Back in the summer of 2005, I got a call to figure out a moisture problem in a new house. The homeowners took me into the primary suite, where the commencement thing to take hold of my eye was the towel folded neatly on the floor. It hadn't only fallen out of the laundry basket; it was there to catch the water dripping from the air conditioner supply vent in the ceiling directly to a higher place. Another one was on the other side of the bed, and those two vents were dripping steadily. It didn't take me long to find the trouble.

Air conditioner vents get cold. H2o vapor loves cold surfaces. Sometimes it leads to mold, as you can see in the photograph in a higher place. Other times information technology leads to the paint coming off and rust forming on the vent (photo at bottom). If you're lucky, it's just an occasional nuisance that doesn't pb to long-term harm to the supply annals, indoor air quality issues, or the need for towels on the flooring. And if y'all're really lucky, yous wonder why I'm even writing virtually this considering you've never seen it.

One cause, multiple reasons

At that place are a lot of reasons why this happens, but there's only one crusade. Let'southward start with the cause. Condensation occurs simply when boiling air is in contact with a cold surface. If your air conditioner supply vents are sweating, you take a cold surface (the vent) and most it you accept air with water vapor in it. The threshold for condensation to occur is that the temperature of the cold surface has to exist below the dew point of the water vapor in the nearby air.

That'southward simple, right? Boiling air with a dew indicate above the temperature of the supply vent causes condensation. Now, every bit for the reasons, nosotros tin start with the 2 big ones. Either the air is too humid (dew bespeak likewise high) or the supply vent is too common cold. That means the fixes are just reducing the humidity of the air or raising the temperature of the vent, depending on which of the ii reasons is causing the problem.

Dew point and the temperature of conditioned air

But how practise you tell which is the culprit? Is the dew point too loftier or the supply vent too common cold? The special number here is 55° F. Well, it'due south special if you keep your house at or shut to the indoor design atmospheric condition recommended by the Air-conditioning Contractors of America (ACCA). Those weather are 75° F for the indoor temperature and fifty% relative humidity. Those conditions correspond to a dew signal of 55° F, our special number.

If you don't keep your firm at 75° F and fifty% relative humidity, the table above shows the relative humidity levels that correspond to a 55° F dew indicate when you go beneath or above a temperature of 75° F. As y'all tin can see, the colder you keep the house, the higher the relative humidity can be to proceed your 55° F dew signal. Conversely, if yous go on the business firm warmer, you have to keep the relative humidity lower or the dew signal will rise above 55° F.

Simply what if yous're non on or close to ane of those lines leading to a 55° F dew bespeak? The higher your relative humidity is, the higher the dew point is at a given temperature. That means you're more likely to get condensation because the supply vent doesn't accept to exist equally cold. At a temperature of 75° F and relative humidity of 60%, for instance, the dew betoken volition exist lx° F. A supply vent at a temperature of lx° F or below will sweat in that instance.

If your indoor temperature and relative humidity are at or close to any of those rows in the table above, your dew signal is about 55° F. That means every bit long as the vent itself is warmer than 55° F, you shouldn't meet any sweating. How common cold is conditioned air? When information technology comes off the cooling coil, it's usually about 55 to threescore degrees Fahrenheit. By the time information technology reaches the supply vent, information technology might be a chip warmer, depending on where the ducts are located and how well they're insulated. Even if the air gets to the vent at 55° F, though, the vent itself is in contact with the warmer room and probably will be warmer than the air passing through it.

The starting signal of figuring out whether your trouble is humidity or supply vent temperature is to measure them. Getting the indoor air temperature and relative humidity isn't difficult, and in one case you have those you can hands find the dew point. The Dew Betoken Calculator website makes information technology piece of cake with sliders for the 3 variables. Once you lot've determined whether humidity or vent temperature is the culprit, yous're in a position to eliminate the problem.

Why the indoor humidity might be as well high

Hither in the southeastern United States, the summer dew indicate is oftentimes in a higher place 70° F. The more of that loftier dew indicate outdoor air that gets into your house, the higher your indoor dew bespeak will exist. In some places, like condos on the beach, that outdoor humidity gets into the business firm because people open the doors and windows while the air conditioner is running. Like shooting fish in a barrel fix: Close the doors and windows.

More likely, the house stays too humid considering of unintentional infiltration. Most houses are too leaky. The fix is air sealing. Get a blower door test, seal upwards equally many leakage sites as possible, and the indoor humidity will become down in summer. A business firm above a vented crawl space is continued to a big source of humidity, peculiarly when it has holes as large as the bathtub drain hole shown below. Encapsulate and condition the crawl space or make the flooring above the crawl space airtight.

Ane way that outdoor air gets inside intentionally is through ventilation. When you plough on a bath fan or a range hood, yous exhaust indoor air and cause outdoor air to come in. Clothes dryers do this, too. On the whole-business firm ventilation front, estrus recovery ventilators (HRVs) bring in outdoor humidity; free energy recovery ventilators (ERVs) as well bring in humidity but less than HRVs. (An ERV is not a dehumidifier.) Ventilating dehumidifiers reduce the humidity.

If the house doesn't accept a lot of infiltration and isn't over-ventilated, look for indoor sources of humidity. Some possibilities are:

Showering without running the bath fan
Doing a lot of cooking
Having a lot of aquariums (You know who yous are, afishionados!)
Steam showers, hot tubs, indoor pools, water features

Two more than humidity trends are working confronting you lot, besides. New houses keep getting more insulation and air sealing, which reduces the cooling load so air conditioners don't run as much. Besides, some of the more advanced ac systems have less ability to remove moisture. In some cases, the merely mode you tin become the humidity low enough to prevent the vents from sweating is to utilize a dehumidifier.

That humidity's got to exist coming from somewhere. Your two fixes here are to reduce the source of the humidity or use a dehumidifier.

Why the supply vent might be too cold

If the indoor humidity is OK, the AC vents however can sweat if they go too cold. The two master causes of excessively common cold vents are low refrigerant level and low air menses through the system. You'll need an HVAC company to check the refrigerant level, just you may be able to practise something about low air menses. Hither are some of the principal causes of low air menses:

Dirty filter
Excessively restrictive filter
Return or supply vents blocked by article of furniture, rugs, or other items
Dirty cooling coil
Excessively restrictive duct system

You'll probably need to hire a pro for the last ii, but if you suspect low air flow, the kickoff matter to do is check the filter. Then check to run into if all the vents are unblocked and the louvers open.

I've also heard of cases where the air flow was too depression in multi-stage or variable capacity air conditioners operating at low speed. Ideally, the refrigerant and air menstruum modify together in just the correct amounts, but complex systems don't always practise what y'all want them to do. Sometimes the air period is fine at 1 speed but too depression at another speed. In addition, multi-stage or variable capacity air conditioners are designed to requite you long runtimes. If cold air is always blowing out of the vents in a house that's on the edge of having sweating vents, that might exist just enough to get those vents wet.

Showtime with the nuts

The cause of sweating vents is simple. Air that's humid enough finds a surface common cold plenty. When vents showtime beading upward with water—or worse, dripping—either the humidity is as well high or the vent is too cold. It's not difficult to effigy out which of those 2 is the culprit. Just notice the dew betoken of your indoor air. If it's close to 55° F, the problem lies with the vents beingness also common cold. If it's to a higher place 60° F, the problem is probably the indoor humidity. From there, you lot can sort through the potential sources of humidity or low air menses to encounter if yous can set the problem yourself. Otherwise, call in an HVAC pro to find the problem and end those vents from sweating.

Oh, you lot're probably wondering about that house with the dripping supply vents in the master suite. Turns out it had a problem with humidity, not supply vent temperature. They had spray foam insulation installed beneath the roof deck to encapsulate the attic and arrive part of the conditioned infinite. But the spray foam contractor missed office of the eave, and then it wasn't sealed well.

To brand matters worse, the master bedroom had a tray ceiling with a gap all the way around, connecting the bedroom to what should have been a sealed attic. Negative pressure level in the cranium from duct leakage and in the master bathroom when the frazzle fan ran pulled in boiling Georgia air, and it didn't mind the gap. It got into the sleeping accommodation through that tray ceiling gap, finding those nice, cold air-conditioning vents. The spray cream contractor sealed the eaves, and the trouble went away.

Allison Bailes of Atlanta, Georgia, is a speaker, writer, building scientific discipline consultant, and founder of Free energy Vanguard. He is also the author of the Energy Vanguard Blog. You tin follow him on Twitter at @EnergyVanguard.

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