Why Do Toilets Sweat? (+How To Stop Toilet Condensation)

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You know summer is around the corner when temperatures begin to rise, you see ants around the house, and — yikes — you notice the toilet sweating!

Sadly, yes, a perspiring toilet is a sure sign of summer. And it’s a dilemma millions of homeowners face each year. You may have encountered it yourself, and considered it a small nuisance. But if left unchecked, a sweaty toilet can lead to bigger problems later. 

Beads of “sweat” can roll down and drip onto the floor, leaving puddles on the vinyl tiles. Moisture can seep into the plywood subfloor,  trickle onto the joists, and cause eventual rotting.

Molds and mildew can also develop, staining the baseboard molding and turning the bottom of the drywall soggy. All of these can require costly repairs that no one wants to have to deal with.

Why Do Toilets Sweat?

Bathroom with white toilet
Bathroom with white toilet (Image: rizzidesigns)

But don’t panic. A sweaty toilet isn’t caused by a leak or backflow inside the tank. It’s simply a sign of water condensing, like when you take out a cold bottle from the fridge and the warm, humid air in the room makes it sweat. Any container holding cold liquid inside, when suddenly subjected to warm, damp air, ends up perspiring.

Thankfully, there are ways to deal with it.

How to Prevent Condensation On Your Toilet 

Use a drip pan

The easiest and cheapest remedy is to catch the dripping water so it doesn’t fall on the floor. Simply place a tray under the tank as a short-term solution until you can find a more permanent one. It’s a quick fix, but you’ll have to deal with the sound of constant dripping when you’re in the bathroom. You’ll also need to empty the tray periodically — maybe several times in a day when it’s extremely hot and humid.


Make it a rule for everyone in the house to crack the bathroom window * and flip the vent fan on when using the bathroom. [*But not if the temperature outside is warmer.  Otherwise, it would just encourage more condensation.]

They can leave the fan on for an extra 10 to 15 minutes after showering to make sure all of the warm, damp air has blown out. If the person is alone in the house, he can also choose to leave the bathroom door open while showering.   

Take shorter showers

Long, hot baths will raise temperatures in the bathroom and cause more toilet sweating. Advise everyone to just take quick showers at cooler water settings. Quick, cool showers are more refreshing and invigorating and save water anyway.

Insulate the tank

Plumb Pak K836-22 Toilet Accessory, Liner, Tank Insert, White
Toilet Insulation Kit (Image: Amazon)

Purchase a toilet tank insulation kit which consists of a sheet of foam that you stick on the inside walls of the tank along with an adhesive application tool. (Some come with self-adhesive backing.) The foam will line the interior of the tank, preventing the heat outside from getting in. It’s an excellent solution especially for houses with their own deep-water wells that supply cold water. For tips on how to prep your tank before insulating it, you can watch this video.

Wrap it up

You can either purchase a pre-made tank cover or make one yourself using an old towel. Sew snap buttons or velcro on each end to secure the wrap in place. Much like a sweatband on an athlete’s forehead, the cover will absorb any condensation that collects outside your tank. Just remember to wash and dry it every week to prevent any buildup of mildew.

Use A Small Dehumidifier

Ivation 13-Pint Small-Area Desiccant Dehumidifier Compact and Quiet - With Continuous Drain Hose for Smaller Spaces, Bathroom, Attic, Crawlspace and Closets - For Spaces Up To 270 Sq Ft, White
13-Pint Small-Area Desiccant Dehumidifier (Image: Amazon)

An air-conditioner will bring the bathroom temperature closer to the temperature of the water inside the tank. There are small, portable models that let you roll the unit to the exact where you need it, such as just beside the toilet. 

A dehumidifier will help reduce moisture in the air, making the room less hospitable to molds and mildew.

Install an anti-sweat valve

Mueller Industries B and K Industries 109-503RP Anti-Sweat Toilet Tank Valve
Anti-Sweat Toilet Tank Valve (Image: Amazon)

Also called a “tempering” or “mixing” valve, an anti-sweat valve is placed in the water supply line leading to the toilet. It adds a little hot water to the colder water in your tank, approximating the water temperature to the ambient room temperature. Some models allow you to adjust the temperature and shut off the hot water inlet off-season. 

An anti-sweat valve can be installed below the floor — if there’s a crawl space or basement — or behind a wall. It may involve cutting and soldering pipes, so unless your water lines are accessible from the basement, and your D-I-Y plumbing skills are top-notch, you’ll need to get a professional plumber to do the installation for you.

Invest in a tempering tank

Purchase a toilet with a temperature-increasing (tempering) tank. It works similarly to an anti-sweat valve, except that the cold water line feeds into a second tank which pre-warms the water before it goes into the toilet. Installing it would require enough space for the tank and open access to the water lines. You’ll likely need a pro to do it for you, too.

Buy an insulated tank

If you have an old tank model that’s uninsulated, you may be able to find a new one that’s insulated and compatible with your existing toilet. Note down the brand and model of your toilet and search online for a compatible tank that’s already insulated.

Upgrade To Water-Efficient toilet

If your current toilet is due for an upgrade anyway, consider getting a low-flow or low-flush model that uses less water. Low-flow, water-efficient toilets have smaller tanks which means they hold less cold water that’s prone to condensing. 

Many people who live in older homes don’t have tanks like those. But since 1992, U.S. law has mandated that new toilets sold in the United States be low-flow, which means that they consume no more than 1.6 gallons per flush. (Before then, typical American toilets used 3.5 to 7 gallons per flush.)  

As an alternative, you can get a dual-flush toilet which uses about .9 gallons per rinse for liquid waste and the standard 1.28 gallons for tougher jobs.

Overall, most of these modern toilets already come with insulated tanks.

Featured Image by philEOS