FAQs on causes & cures of / for condensation on plumbing pipes, tanks, toilets.

This article series gives the causes, significance, and cures for condensation or "sweating" on plumbing system components like pipes, water tanks, and toilets.

What is Sweating or Condensation on Plumbing Pipes, Tanks, Toilets

These questions and answers about "sweating" or condensation on pipes and on plumbing fixtures were posted orignally at CONDENSATION or SWEATING PIPES, TANKS - be sure to see the explanation, diagnostic advice & cures given there.

Question: what can I do to stop moisture from condensing on the bathroom ceiling & trim?

We have floor ac/heat vents. In master bathroom, we have ventilation fan over the toilet, there is warm air seeping from the attic through the vent and cool a/c coming up from the floor vent.

(I think) This is causing the moisture to form on the ceiling and crown molding of the bathroom. What can I do to stop it? We live in very humid Alabama. - L.F. 9/4/2013

Reply:

Thank you for the interesting question - it helps us realize where we need to work on making our text more clear or more complete. A competent onsite inspection by an expert usually finds additional clues that would permit a more accurate, complete, and authoritative answer than we can give by email alone. You will find additional depth and detail in articles at our website.

That said I offer these comments:

Causes of down-flowing air in buildings

First, it's unusual for warm moist air to flow downwards from an attic or roof space into a bathroom or other room below, and indeed if warm moist attic air enters a cooler indoor space the moisture carried in that air might be expected to condense or collect on cooler building surfaces.

Such downflowing air in buildings, contrary to the usual upwards convection currents in buildings, can indeed happen for several reasons, all of which have one of two basic underlying causes. Either

• Room depressurization:
  
  the room into which attic air is flowing down has been de-pressurized compared to the attic air pressure, perhaps by a powerful exhaust fan
• Cooler room air flows downwards:
  
  the room into which the warm moist attic air flows downwards is filled with air that has been chilled, say by central air conditioning, sufficient that the cooler air flows out of the room and downwards to lower building floors or spaces, thus creating a downdraft.

In both of these cases the room is basically "sucking" warm moist attic air downwards from above, with that air passing through any openings it can find, such as around a ceiling vent fan or light fixture.

The cool air coming up from the floor is not itself "causing" indoor condensation, but the cooler indoor temperatures it creates as well as possible downflow of heavier cool air in that room could be factors in the condensation or moisture collection you describe.

How to fix down-flowing moist attic air leaks & related indoor condensation

• Improve or correct the attic ventilation system,
  
  making sure that there is both adequate soffit air intake and roof ridge vent air outlet.
  
  See ATTIC CONDENSATION CAUSE & CURE
  
  and SOFFIT VENTILATION if you need details.
  
  For a thorough discussion of proper roof ventilation designs begin
  
  at ROOF VENTILATION SPECIFICATIONS..
• Seal openings 
  
  in the room ceiling such as around the ceiling vent fan and light fixtures.
  
  Details are at AIR BYPASS LEAKS and
  
  at AIR LEAK SEALING PROCEDURE
• Use indoor vent or exhaust fans:
  
  be sure that the bathroom (or kitchen) exhaust fans are properly ducted to outdoors, adequately sized, and are used when moisture is being generated indoors by bathing or cooking.
  
  See BATHROOM VENTILATION CODES SPECS
  
  See VENTILATION, EXHAUST ONLY
  
  For better energy conservation, we discuss the benefits of balanced ventilation
  
  at  VENTILATION, BALANCED - an approach that can reduce both heating and cooling costs
  
  VENTILATION, BALANCED HEAT COST SAVINGS
• Check for duct leaks & check attic moisture levels:
  
  don't forget to inspect the attic to be sure there is no ongoing water or leak problem such as a roof leak or ice dam leaks or condensation collecting in and leaking back out of HVAC ducts or vent fan ducts routed through that space
  
  . For ducts routed through the attic also check for missing or damaged duct insulation; any of these conditions can cause moisture to collect in and leak out of ductwork in the attic.
  
  See AIR LEAKS in RETURN DUCTS
  
  and AIR LEAKs in SUPPLY DUCTS

Reader follow-up:

We finally got it fixed, we added a larger vent fan to bathroom, but that didn't seem to help

We took temp. readings from the floor vents, the temp. of the air was 34 degrees (first vent, closest to AC unit). We closed it almost all the way and that reduced the moisture and (so far) we've had no more problems. Thanks! R.F. 12/4/13

Thanks R.F. for the followup; it sounds as if by reducing the extent of cooling in the bath you reduced condensation that was occurring there. When you cut back on cooling in the humid bathroom you gave the vent fan a chance to exhaust moisture outside, and by warming the bathroom surfaces you're reducing the rate at which condensation forms there.

Question: A/C condensate drips into sink in a nursing home

(May 7, 2012) Lemastre said:

In a nursing home I noted a 3/4" copper pipe protruding an inch or so down from the ceiling and dripping water into the sink directly below.

The nursing home uses a tempered-water heating/cooling system, so there are pipes and maybe even a heat-exchanger in the ceiling over each living area. What does a building code usually say about disposing of condensate in such a system?

Reply:

Lemastre

If the water you see dripping into a sink is A/C condensate there is a risk of legionnaire's disease and the installation is unsafe.

Question: toilet sweats a lot, how can we fix it

(June 20, 2012) Jo said:

The tile flooring in our toilet sweats alot I think this is due to the clay base if it has been raining for some time. How can we prevent this.

2015/12/16 Jill said:
We have very cold well water and our toilet, and some of the pipes inside the house that are exposed to air, sweat.

My question is two-fold. Should I worry that the pipes hidden in the walls are also sweating? and If the toilet tank and bowl are sweating, is it possible that there is unseen sweating beneath the toilet pedestal that I can't see?

I've pulled up the tiles around the toilet to dry the subfloor, but there is a little wet spot emanating from the side of the pedestal beside the bolt, but I don't think the toilet seal is leaking. What do you think? Thanks.

Reply:

Jo, since it is usually not at all cost feasible to chop up a concrete floor to insulate below it, what remains to stop condensation on a cool floor surface is to reduce the indoor humidity level.

That means running a dehumidifier as well as finding and fixing any indoor leaks or moisture sources.

In a small bathroom where there is not good air circulation, the condensation problem may be worse than elsewhere on the same floor.

A small fan that increases air circulation across the floor might also help. But try a dehumidifier.

But first, check for a toilet fill valve or flush valve that's leaking, causing a running toilet - the most common cause of excessive condensate formation on toilet tanks and bowls.

Jill

Except during times of heavy use I don't expect to find condensation on toilets, even when the water supply is quite cold, except when the toilet is actually leaking or running. Often a running toilet is a bit subtle so you may not be aware of the problem.

See TOILET RUNS CONTINUOUSLY

Yes there can be unseen sweating - which is actually condensation since water is condensing out of the air onto the cool surface; water is not actually moving through pores in the toilet or pipes onto the component exterior.

And yes there can be hidden damage in walls or floors, though on cold water pipes condensation is less likely to occur in an insulated wall cavity than on an exposed cold pipe routed through open air in a locale of high humidity.

Besides checking for running toilets (that can also explain extra condensation on cold water supply pipes as well as flooded septic fields), also check that you don't have a avoidable indoor moisture source that is raising the indoor humidity.

Question: condensate on sewer pipe

(Jan 2, 2013) Diane V. said:

We have cast iron sewer pipe in the basement and it condensates and drips rust-colored drops.

The previous owner had wrapped a plastic garbage bag around part of it, but we'd like to know how to keep it from happening.

We can't find a leak source. I'd like to move our chest freezer to under where the pipe runs down to make more space in the laundry area, but can't until we get this drip figured out...I don't want it dripping all over the freezer!

Reply:

It sounds to me as if there is a leak; cast iron can have a hidden crack or on occasion rust perforation. A thorough inspection is needed. I agree that it may be unsanitary

Question: solar panels and attic condensation

(Jan 9, 2013) michael said:

can solar panels cause condensation in attics

Reply:

Michael that'd be unusual. More likely there is an indoor moisture source or the attic is not properly ventilated, or both.

Question: aquarium heater used in toilet to stop condensation?

(1 days ago) Nicholas Alipaz said:

I was able to quickly solve my toilet sweating problem by placing a small standard aquarium heater into the tank.

I have an outlet just below my toilet to plug in the heater, so it was quite easy.

The rule for these heaters however is to always keep them immersed in water to avoid breaking them, however I found that the very short amount of time whilst the toilet tank is filling with water after a flush has no visible ill effect on the heater. I have had the same heater in my tank for 2 years and it is still going strong.

Reply:

(1 days ago) (mod) said:

Interesting idea Nicholas. I would take the solution to toilet tank just one step further and make sure that the toilet is not running. Sometimes that sort of leak is ot immediately obvious. We don't want to fix joist the symptom if there is an underlying problem to be addressed.

For example a running toilet wastes water and floods septic leachfields.

On 2018-08-07 by (mod) -

To reduce condensation on cold Plumbing components of any sorts there are two fundamental approaches

One is to reduce the humidity level in the area

The second is to insulate the surface on which condensation is appearing

On 2018-08-07 by Pankaj

How to avoid sweating from chilled water valve and flange joint from insulation

On 2018-07-26 by Fred

I have well water and the holding tank seats a lot. How ca I fix that problem?

On 2018-02-16 by (mod) -

Jerrie

No, not unless the "excessive water pressure" is causing leaks or water spills.

On 2018-02-15 by Jerrie Kent

Does excessive water pressure coming into the house make the problem of condensation worse?

On 2018-01-10 by (mod) -

"Stopping the damp in the wall" leaves me confused.

Opening the wall to insulate the cold water pipes to stop condensation on the pipes and to check for leaks might be appropriate.
Steps to check for and seal air leaks into the wall might also help.

If the wet wall is drywall it is inviting mold growth so cutting it away to get to the pipes isn't giving up much.

On 2018-01-10 by chris

We have a fairly severe damp patch on our internal wall and condensation issues in the same room on the windows, the cold water pipes that serve the other (4) flats in the building are running through the room (boxed in) and apparently this is the cause of the damp patch, condensation on the pipes.

The solution we were offered was one of stopping the damp in the wall but it doesn't seem to offer a solution to the damp / condensation forming in the first place. How would we go about that?

On 2017-09-03 by Norm MacDonald

We have had to water leaks in our cement basement. We have copper pipes and the repairman has repaired the two leaks with plastic pipe. Shall we have
him replace all our copper pipes with this plastic pipe, and shall we have a fan in the basement/crawl sites to blow out the moisture

On 2017-01-15 by Anonymous

Why is my septic rant sweating?

On 2017-01-10 by (mod) -

I'm not sure what a kitchen "rv" is.

But "sweating pipes" are, as noted in this article, condensation of moisture out of warm moist air onto colder piping surfaces. So insulating the piping is a smart idea. It doesn't need to breathe and your insulation will work better wrapped as you describe.

Best if you don't wrap wet pipes though. Dry them off before insulating and wrapping or you may grow mold in the insulation.

On 2017-01-09 by Michelle Perry

My kitchen in my rv is sweating a little underneath. I checked the pipes, and their is no actual leak. I wrapped plastic around it to stop it. How5, should i let it breathe?

On 2016-12-20 by (mod) -

Joe

Thanks for the interesting question. A hot water supply line that suffers night sweats is probably actually getting cold at night and is located in a wet or moist area that thus causes condensation. OR there is a leak that shows up at low temperatures. I'd try gently tightening the cap nut that compresses the washer around the valve stem.

On 2016-12-20 by Joe

I have a hot water supply valve that is sweating at night. The weather has been quite frosty recently.

The valve has a pool of water in the morning under it. During the day when the weather has warmed up it stays dry. It is the only valve that has the problem.

Other than insulating the valve, could it be anything else?

On 2016-10-12 by Sarah

I've a combi heating system and a pipe in the old boiler cupboard was showing condensation drips. I've followed advice to insulate them but now the insulation is soaked and the smell of damp is rife. What do u suggest next.

On 2016-06-17 by (mod) -

I would certainly look into the ceiling as well as in the bath above; it's essential to understand the cause of the leaks and to fix it. Don't just insulate pipes until you know that condensation is the only problem - something I question.

Search InspectApedia for HOW TO CLEAN UP MOLD for advice.

On 2016-06-17 by pam

I have an issue with dripping water from ceiling above, which is another bathroom. We previously had an issue with water damage from ice dam, had that replaced and fixed, but it got very humid and leaks started again. Should I take look and insulate the pipes? the house was built in 1962. We now have a molding issue too. thank you.

Pam

On 2015-12-16 by (mod) -

Jill

Except during times of heavy use I don't expect to find condensation on toilets, even when the water supply is quite cold, except when the toilet is actually leaking or running. Often a running toilet is a bit subtle so you may not be aware of the problem.

See TOILET RUNS CONTINUOUSLY

Yes there can be unseen sweating - which is actually condensation since water is condensing out of the air onto the cool surface; water is not actually moving through pores in the toilet or pipes onto the component exterior.

And yes there can be hidden damage in walls or floors, though on cold water pipes condensation is less likely to occur in an insulated wall cavity than on an exposed cold pipe routed through open air in a locale of high humidity.

Besides checking for running toilets (that can also explain extra condensation on cold water supply pipes as well as flooded septic fields), also check that you don't have a avoidable indoor moisture source that is raising the indoor humidity.

On 2015-12-16 by Jill

We have very cold well water and our toilet, and some of the pipes inside the house that are exposed to air, sweat. My question is two-fold. Should I worry that the pipes hidden in the walls are also sweating?

and If the toilet tank and bowl are sweating, is it possible that there is unseen sweating beneath the toilet pedestal that I can't see?

I've pulled up the tiles around the toilet to dry the subfloor, but there is a little wet spot emanating from the side of the pedestal beside the bolt, but I don't think the toilet seal is leaking. What do you think? Thanks.

On 2014-11-04 by (mod) -

Anon

It sounds as if the vent fan duct needs to be insulated and have its routing checked to be sure there are no low spots that accumulate condensate.

On 2014-11-04 by (mod) -

Mary those ceiling stains suggest either roof leaks or condensation traps in the ceiling.

On 2014-11-03 by Anonymous

newly refinished bathroom. now that the cooler weather in the northeast is here. the vent stack has condensation.it runs out through the vent fan.

i thought that was the culprit. it is not. how will i stop the condensation from ruining the drywall on the ceiling. should i wrap the vent stack with some type of insulation?

On 2014-10-27 by Mary

There are numerous brown stains on the ceiling in my the trailer that tend to be on both sides ofthe brown wood strips nailed vertically across the ceiling in my kitchen, but there is also a brown stain around the light fixture in the kitchen which leaks when it rains to the point where there is now a hole in the ceiling beside the light fixture.

However now there is one stain in the bedroom wood strip that leaked without rain. So I am trying to determine if the two are connected or if only the bedroom one could be condensation since it has its own shower.

There is no door separating the bathroom from the bedroom. I hope I gave enough details for you to be able to provide inout.

On 2014-09-26 by (mod) -

IN short, yes. Often bath exhaust fans move too little air too slowly to overcome lots of steamy bathing.

On 2014-09-17 by Rachel

Hi
I read through the above guide with interest and found it very useful. I will really appreciate if you can help me unearth the cause of constant issues in the bathroom of my flat that is let out. In the last two years i have had water leaking through the tiles as the grout started to break.

The bathroom was redone to very high standard so i know it was no short cut applied when it comes to tiling the bathroom. The water usage is quite high according to meter readings.

A few times i have seen above average amount of steam in the bathroom when i have attended the property myself. I have seen walls dripping in water, floor covered in water and recently ceiling had water droplets at least 10 min after last shower use

. I have an extractor fan and window. The reason I am raising this question is recently i visited again following more water leak and i noted quite a lot of condensation on the cold water pipe and reading your article I am hoping i am nearing the cause of the issue. Can having very long/hot showers result in enough steam which increases moisture in the bathroom and it starts damaging the walls and ceiling?

Can it also be the reason to see so much condensation on the cold water pipe? Many thanks

On 2014-09-08 by (mod) -

John, someone has probably tried just about anything any of us can imagine in managing building mechanical and plumbing systems, but in my opinion warming cold water to avoid condensation would be a rather expensive way to address the problem. You want to insulate the pipes so that the pipe surface doesn't reach the dew point, and to find and remove sources of abnormally high indoor moisture.

On 2014-09-08 by John

Hello, looking for help with water pipes that condensate. I wrapped the pipes in the basement because there running above a drop ceiling and was causing damage. Know the pipes in the 2nd floor ceiling are causing damage to the 1st floor ceiling. I wanted to know if anyone has used a whole house tempering valve after the well tank to raise the temperature of the water to eliminate this problem?

On 2014-09-07 by (mod) -

Gina

Indeed condensation in a chimney venting gas fired appliances could be due to UNSAFE heating equipment operation.

I'd ask your water heater and gas furnace installers to check out the system for safety. If they're not up to it ask your gas company for help; also a certified chimney sweep may be able to help.

On 2014-09-06 by Gina

I have a new gas water heater (March 2014) with a vent pipe which ties into the gas furnace vent pipe to the chimney. I also got a new roof (Feb 2014).

About April/May 2014 after a hard rain storm I notice water dripping from the gas vent pipe down into the gas furnace and on the floor below.

I got the roofers out there and they sealed the vent around the chimney really well. Problem didn't get solved. I thought it was connected to rain because that is the time I notice it but now I wonder if it is condensation because I don't think it rained last night and moister/drops on the ground (it is very humid today also). Any help or insight would be greatly appreciated.

On 2014-07-09 by (mod) -

Dave, if the water ever is hot we know it's from the heaer.

If its a gas or oil fired heater take a look in the combustion chamber where you may see leaks.

Check for wetness inside the end of the TP relief valve discharge tube end.

Follos the AC condensate drain with care to see if it's leaking.

On 2014-07-09 by Dave

I have a new 40 gallon tank gas hot water heater which sits next to my furnace/central air combination unit all located in a closet in the basement. The central air is now running continuously during the hot weather, and today I noticed a pool of water, which I believe is condensation, coming from under the water heater.

There is not enough visual clearance under the water heater to make an accurate determination of the actual source under the tank. How can I determine if it is condensation, and if it is, how do I correct the problem?

On 2014-06-21 by (mod) -

Sure, DP

In the article above just take a look at the section titled

How to Cure Condensation or Sweating on Plumbing Pipes, Tanks, Toilets

And let me know if that text is unclear or incomplete

On 2014-06-21 by D.P.

WELL BLADDER AND PIPES ON BACK PORCH
NOW IS THERE ANYWAY TO STOP PIPES FROM SWEATING PURFUSELY WICH IT CREATES A MOISTURE MOLD PROBLEM

On 2014-06-07 by Naila

good afternoon. my apartment is in block building. 3 walls my bathroom are made of briks. hot and cold water pipework is hidden in the walls. outer side of the walls are covered by wallpaper. since last autumn the wallpaper is detached from lower parts of all 3 walls due to humidity inside walls. mould and insects are observed. air in the apartment is not wet. please advise the possible reasons and best solution for the problem. thank you.

...

Continue reading  at CONDENSATION or SWEATING PIPES, TANKS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• AIR BYPASS LEAKS
• ATTIC CONDENSATION CAUSE & CURE
• BATHROOM VENTILATION CODES SPECS
• BIBLIOGAPHY for ENVIRONMENTAL HEALTH, MOLD, IAQ
• CONDENSATION or SWEATING PIPES, TANKS
• DEW POINT TABLE - CONDENSATION POINT GUIDE
• FORENSIC INVESTIGATION of BUILDINGS
• HOUSEWRAP AIR & VAPOR BARRIERS
• HUMIDITY CONTROL & TARGETS INDOORS
• MOISTURE PROBLEMS: CAUSE & CURE
• MOLD on TANKS, WATER, OTHER - photos of mold growth on water pressure tanks and comments on where the health hazards may lie
• VENTILATION in BUILDINGS
• VENTILATION, BALANCED HEAT COST SAVINGS
• VENTILATION, EXHAUST ONLY
• SOFFIT VENTILATION

Suggested citation for this web page

CONDENSATION SWEATING PIPE or TANK FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to PLUMBING SYSTEMS

Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia

Ask a Question or Search InspectApedia

Try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Note: appearance of your Comment below may be delayed: if your comment contains an image, photograph, web link, or text that looks to the software as if it might be a web link, your posting will appear after it has been approved by a moderator. Apologies for the delay.

Only one image can be added per comment but you can post as many comments, and therefore images, as you like.
You will not receive a notification when a response to your question has been posted.
Please bookmark this page to make it easy for you to check back for our response.
Our Comment Box is provided by Countable Web Productions countable.ca

Citations & References

In addition to any citations in the article above, a full list is available on request.

---

ADVERTISEMENT

---