BS4D: The case of the Sweating Toilet

Ok, we know the toilet really isn’t sweating over the burial at sea of one aforementioned Barbie doll, performed with full military honors by none other than one little Timmy… so why is it sweating? The short answer is it’s not; it simply is the water in the air (humidity) condensing on a cold surface (dew point). You generally see this happen during the summer with an ice cold glass of sweet tea or bottle of your favorite brew. In some cases you might see it when water starts condensing on your windows during winter.

While we could discuss grains of moisture, dew point, Psychrometric charts, hygrometry, and your eyes rolling to the back of your head, let’s not & instead focus some common & not so common fixes and then deal with the real issue & how to solve them.

Common fixes:

One of the most popular fixes is running to a hardware store & explaining your issue to the guy in the plumbing area where they will point you to; (from cheapest to more expensive)

An in bowl insulation kit
- Pro: Relatively inexpensive & if it prevents the bowl from getting cold it won’t sweat on the sides plus it might reduce water usage some
- Cons: Unless the bowl is cleaned perfectly, the glue being mixed & applied perfectly & the toilet sits for the required 12 to 24 hours the kits tend to fall off, block stoppers & make a mess of things. Most kits also do not insulate the bottom of the bowl where condensation can still occur
A sweater for your bowl aka a glorified shag rug or cover for your toilet
- Pro: No cold back when you sit down & it does cover parts of the bottom of the bowl
- Cons: No full coverage which still allows for condensation to form & become a food source for mold growth
A mixing valve to warm the water entering the tank:
- Pros: They have an adjusting valve to get the right amount of hot water, a shutoff & it takes care of not only the tank but the supply line & connection.
- Cons: Generally they need to be installed by a licensed plumber, needs adjustment to get the right tempering level (for many places due to long water runs that means 0% cold 100% hot), & wastes energy if you forget to turn it off when not needed

A few uncommon fixes:

While this one was accidental, some people have resorted to piping hot water directly to the toilets to eliminate the issue. Do I really need to say that isn’t such a bright idea? Let me give a quick shout out & say thanks to Kevin Hergert of Hergert Inspection for allowing us to use this shot. If you get a chance he has some great infrared shots on his site worth checking out.

While uncommon it is worth checking the toilet for leaks which should be done every so often anyway. A toilet that is constantly running will remain cool instead of getting a chance to warm up. To see if it is leaking, just pop the lid off the tank & place a few drops of food coloring in the tank. Come back 15 minutes later & check the bowl, if the water in the bowl has changed colors you need to fix the toilet. If this does stop the “sweating” you might be in luck.

Replacing the toilet: In all fairness, I don’t have an issue with replacing the older 3.5 to 5 gallon ones which commonly have this issue. Some on the other hand will advocate replacing a newer 1.6 gallon one with a pressure assisted one as it has a secondary tank inside preventing the tank from being exposed to the cold water. If you do have a newer 1.6 gallon toilet the issue is probably larger than just the toilet.

Dealing with the real issues:

The real issue is two fold, you have a surface that is cool enough to form condensation on due to the incoming water temperature and a high level of moisture in the air. Sure the toilet is sweating which can cause all sorts of flooring issues, but what about what you can’t see. The water doesn’t just arrive at the toilet does it? The copper pipes run in wall cavities & the damage can be quite interesting to say the least.

In the wintertime it is pretty obvious that when you take a hot steamy shower the mirror fogs up & the toilet may appear to be sweating. In this case by turning on the fan not only while you take a shower but leaving it on after you have finished will eliminate that issue. The same holds true in the summer, (yes even if you are taking a cold shower) as you are releasing water vapor into the air. Close the lid on the toilet, as the act of flushing the toilet releases water vapor into the air.

Air leakage is one of the biggest transport mechanisms for pulling humid air inside, whether from outside the house, from the basement, or a crawlspace – especially an unsealed crawl space
Run a dehumidifier &/or the AC to help pull moisture from the air 40 – 50 RH is your target depending on how warm you keep your house & what the water temperature is (the warmer you keep your house, the lower you want the relative humidity value)
Don’t forget to run your vent when cooking, especially if you are boiling something or cooking with gas
While plants are nice to have in the house, they are best left outdoors during the summer as they also release water vapor (if you can keep the humidity down & the water temperature up this point is moot)

In some cases because of the incoming water temperature you won’t be able to pull enough “humidity” from the air without running into that dreaded “you shocked me” & in this case you need to find a way to raise the temperature of the water or prevent the moist humid air from reaching the pipes & the toilet

Insulate the pipes – in most cases this is easier said than done, sure you might hit a few runs in the crawl space or basement, but what happens when it goes into the wall? What happens when you reach the shutoff?
If you are re-piping or building new, skip the copper & go with PEX, PVC or CPVC as it has a little more insulation value
Place the tempering valve back where it will do the most good, where the water comes into the house. In many cases you just need to bring the temperature up a few degrees. Set reminders to turn it off.
Get a cheap 2^nd water heater and use it as a storage tank. This allows the water to come up to room temperature without it sweating all over the place & when water is drawn from it the incoming water is tempered with what is in the tank.

Psychrometric charts are a great tool once you learn all the terminology & how to use them. With that said, you may not always have one handy & while there are apps for that, batteries do die. There is one quick rule of thumb that can help you figure out the dew point which is to take any given temperature & pretend it is at 100% RH. For every 10% you reduce it, take 3° off the temperature & there is your dew point.