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Heating Moisture and Insulation Q's and A's Window Condensation | Duct/Duct Pipe Sweat | Wall/Ceiling Moisture | Other Questions Can't find a solution to your problem? Post a question in our Forums. Window Condensation We bought a ranch type house with aluminum self storing storms and we have a BIG problem with condensation on the inside of our windows to the extent that a towel has to be laid on the sills for the entire winter months. What is our problem??? The water just runs down the windows and pools on the sills. It means the windows are cold and the house humid.... do you get any condensation on the storm window? if not, then the inside windows are tight. You can try sealing the storms better, but that may be a lost cause. Advertisement Contact me to place your ad here You can try lowering the humidity in the house..? Otherwise you are stuck unless you want to buy new windows.... but even they will sweat some when it is REAL cold and/or the humidity is high. More Condensation on Windows We had new insulated vinyl windows installed and now that the cold weather has started, we are seeing condensation on the windows that is much more evident than when we had the old storm windows. Is this normal? We have a bay window that is vinyl and insulated and it never does this except when it's 10 degrees or more and only a slight amount of condensation. I think there is no normal. But if your new windows are sweating more than the old, and the bay window is still not sweating, then my guess is the new windows are not as good a thermal insulator as the old. There are so many things that can affect the equation though. For instance.. is the humidity level in the house the same? Have you added anything to raise the humidity, like an unvented heater? If the new windows are tighter than the old (a strong possibility) then maybe the indoor humidity is higher due to less air in/out leakage. Anyway.. in general.. if things are the same.. and they are sweating more.. they are not as good thermally. Even More Window Condensation Our house is only 5yrs. old and from day one the windows have sweat. I need help to try to stop this. Wood around the windows is molding. Please help me save my home. This happens in colder weather, so all winter long I have wet windows. I know I live in a high humidity area, but there must be some way I can save my home. Ok.. so by now you know that the sweat is caused by humidity inside the house, and cold window panes. To fix... or at least minimize the problem, therefore you can try to remedy those two causes. For the windows, the best bet is storm windows. These are not cheap of course.. but they will had a significant amount of R value.. Perhaps doubling it even, and that will certainly help. Cheaper alternatives for this are those plastic wraps you can put on the window... But I never like those. For the humidity... do everything you can to keep it low. Use your vent fans when showering.. when cooking.. Do NOT use unvented fireplaces or kerosene heaters. Take a look at our article on this subject at the link below. *http//www.handymanusa.com/articles/condensation.htm Last Wet Window Question I saw a post on this subject a while back but I'm going to ask the question also. I live in a 30+ year old home. I'm slowly getting the windows changed over to double paned, insulated ones. Even with that, I notice I get at times, a certain amount of water buildup on the inside. Would a de-humidifier benefit me? It doesn't do it all the time, only when it damp and cool this time of year. Right now it's in the forties and it has rained off and on all day, and there is water on a few windows. Yes, a de-humidifier may help. The problem, of course, is that there is too much moisture IN THE HOUSE. It is not the fault of your new windows. You mention that the house is 30+ years old. Have you done any weather proofing? Added insulation? The house may have become too tight. The solution, add fresh air. This can be done by adding a fresh air intake into your furnace duct work. If you have a basement, you might want to add a cold air supply. (2" PVC pipe - bore hole through box plate to outside - install elbow with hardware cloth to keep vermin out - another elbow on the inside - run pipe to within a couple inches of the floor. The third option is to install a heat exchanger. A bit costly but it helps conserve your heat while providing you with plenty of fresh air. Why is fresh air important - it is drier! Remember, humidity is relative to temperature. As your outside 40 degree 90% relative humidity air is warmed - its relative humidity drops dramatically! The result, dry windows. Good luck!

Sweating Duct Pipes

I have central air and during the latest hot humid weather the duct pipes have sweat so much the basement floor is wet. Any ideas on how to stop it? Or why this happens?

It happens because like a cold glass of beer on a hot day, the humid air's moisture is condensing on the cold duct. The best fix is to insulate the duct. If the humid air cannot come in contact with the duct, it won't sweat anymore. Another thing you can do to help, is lower the humidity in the basement with a dehumidifier. The basement's air is always relatively high in humidity because the air is cooler down there. The lower temperature means you are closer to the dew point...blah blah blah.. you know.. what the weather man is always talking about. Anyway, if you run a dehumidifier, it will take the moisture out of the air, in the same manner as your ducts are doing now.This generally helps with the mustiness that damp/humid basements are prone to.

Ducts Sweating between Floors & Ruining Ceiling

This week it was so hot the A/C Ducts sweat in the ceiling of the kitchen--we can find no one who has any real solutions ! This happened 5 years ago when the last 115 degree heat wave hit! We wrapped the duct at the source of leak and put a pan under the joint-and finally closed up the holes--until now! We have more spots than before-stretching along the duct which runs from front to back exterior walls/front of house gets the blistering afternoon sun.No other T.H. in neighborhood has this problem! Did they not insulate our house properly ten years ago?Is there a fan we need to install between floors? We are going on common sense alone--help? We can find no local expert who has a clue!


Did you say that you wrapped the duct in insulation? I realize that means opening up the ceiling over the whole length of the duct, but that is what you need to do. The humid air is making contact with the cold duct and the moisture is condensing there. If you open that part of the ceiling, insulate the duct and then fill the entire space between the joists with insulation. The whole thing should be wrapped in plastic to keep any moisture from migrating in through the insulation. Pay attention to the ends of the section where the humid air can be coming in from outside. Once the humidity in your house drops (from using the A/C) this problem should have stopped.
The things that may make your house susceptible are things like.. not keeping your house airconditioned...letting the humidity rise and then trying to cool it off daily. (maybe your neighbors run their A/C constantly) Or maybe that section of your joists has a hole to the outside which is feeding it moisture laden air. Just some thoughts...

Moisture in Carpet: Sweating Air Duct?

I have a spot of carpeting that keeps getting damp, even wet. It is an on and off problem. And it happens only in this one place. After blaming the dog a couple of times it seems that she is not the culprit. I went into the crawl space and there are no puddles on the ground, and there are no
pipes of any kind anywhere near the spot. The insulation under that part of the floor is missing. The other insulation is very wet, the papar backing is even molded in places. There is obvious condensation from the air-co ducts. Could the dampness be from cold air condensing on the subfloor and seeping up?

Where in the country do you live.. and what time of year is this problem noticed.. just now during the cooling season?? I think you are on the right track. The house is cool from the A/C and the floor there is cold enough to condense the moisture coming up from the crawlspace below...What is on the floor/ground of the crawlspace? Dirt? If so, you should cover the whole area with 6 mil polyplastic sheeting. Over lap all the edges (you can even tape the two together..) and run it right to the edges of the wall. Weighting the whole thing down at the edges with 2x4s or something.
Also, get some insulation for that area that was missing it.

Interior Wall Shadowing: Moisture Condensing in Walls/Ceiling?

We are experiencing a problem in the great room of our three year old home. This room has a vaulted ceiling with unheated attic space on each side. Both walls and ceilings in this room are drywall painted white. We have noticed shadowing or gray areas appearing on the walls above the heated area and ceilings specifically on the stud lines and around our recessed can lights. Could this be attributed to differences in insulation thickness or caused by moisture?

Yes I believe it is. Probably you have much higher insulating value in the walls then the studs can provide (wood is only about 1 R per inch) And they usually keep the insulation away from the lighting fixtures to keep them from getting too hot and starting a fire. So those areas are the cold spots. Then, the moisture in the house is probably condensing on those areas which may cause the discoloration or it may be attacting dust which is causing it.

(I doubt it would be moisture coming through... since it generally would be going out from the warm moist indoors to the cool dry outside)

Mold on Inside Walls

I have a problem with mold on the inside of my home. the house had been sided over with aluminum siding, and has new vinyl double pain windows and plenty of insulation in the ceiling. the mold is growing on the inside of the out side walls of the house. what do I need to do to get rid of it.

My guess it is a sort of combination of two things.. Hi humidity (perhaps from a house that is too tight) and cold spots on your walls. To help me here, does the mold grow everywhere or anywhere, or in particular spots. I ask because, if it chooses the same spot all the time, what is happening, I believe, is the wall is getting damp because the insulation has a hole or thin area. If the wall is colder there due to a bad spot in the insulation, the humid air will condense and support mold growth. If it is everywhere and anywhere, then the problem is just the humidity level. You can lower the humidity level by doing a few things make sure you vent off as much as possible such things as, when cooking.. run that range hood vent fan. Run the bathroom fan while taking a shower and until the room clears. It helps to crack the window just a bit while running these fans. Make sure you never vent your dryer indoors. Buring unvented fires add humidity. Kerosene heaters add a BUNCH.. or any unvented fires. including the gas stove and oven if you have one. But.. eliminate the kerosene heater if you have one. If you have done all those things.. and you still have a problem.. you can do some things.. they sell air to air heat exchangers.. which will add fresh (dry) air from outside and use the outgoing indoor heated air to warm it. These can be pricey, and you may want to just try cracking a window in the house... ever so slightly. The thing is to increase the number of air exchanges the house gets. I hope that helps.. this and maybe more are in the article we have on our site.. check out http//www.handymanusa.com/articles/condensation.htm

Moldy Walls

I have a rental home that is collecting mildew on the exterior walls of the house. Certain areas continue to collect mold. What can I do? Do you think I have poor insulation? The house has aluminum windows, which were replaced 4 years ago. What would be most cost effective?

Probably lack of insulation; but you need to curtail the source of moisture first...

Sweating Ceiling

During the winter months, our ceiling sweats along the outside edge. The problem is so bad that mold and mildew will go. The attic is insulated between all the joists but not over the area where the carport is. It is a annoying problem but we do not know how to fix it. Any ideas?

You need to get insulation over the effected area. You also need to make sure if there is a ventilation path from soffit vents up... that the insulation does not block the air flow. But.. the cold ceiling.. is condensing the moisture in the air.. and the mold loves it. Warm the wall surface with better insulation and the moisture won't condense there.

Proper Humidity Level Inside Home

What should the humidity be inside your house?

For comfort and health in the wintertime, relative humidity should be between 30 and 50%.

Crawlspace Ventilation Fan for Moisture Control & Fungus Killer

During annual termite inspection, it was noted that there was wood fungus on floor joists due to high moisture levels. It was recommended to apply a fungus killer and install power ventilation (3 fans). Question is can a homeowner due this as far as applying the fungus killer and where do you get the fans for this application. I prefer placing one that has louvers and is mounted in the crawlspace foundation in an opening of 18" X 18".

If you are handy with tools and electrical wiring you can install this system yourself with a little planning. The parts you'd need (including ventilation fans) are available at most large home centers, although for your problem I would probably go to a HVAC contractor/outlet. The system of ventilation would be controlled by a humidity control unit that would come on/off according to moisture levels.
I would be very concerned that you have so much moisture under your floor joists. If you know the cause of the moisture levels you should go to the root of the problem and correct it (e.g. failed or no drain tiles around your foundation). But if there is minimal options you need to certainly get on with doing something to dry the space under your floor.

Eliminating Odor by Insulating Crawlspace?

I live in a rambler on a crawl that was built 50 years ago. We remodeled the inside of the existing house and built an addition on to it. After getting new carpet throughout, the floor in the old portion of the house seems to be emitting a mildewy odor. When the house was remodeled, plastic was placed in the crawl and the insulation value was increased. Under the carpet are some old tiles that look to be almost as old as the house. My suspicion is that the crawl space was not insulated well and had no plastic in it until about a year ago caused the wood subflooring to mildew and the smell has resurfaced through the new carpet. I want to rid myself of this odor. Can I get away with stripping the tiles, applying a sealer to the sub-flooring, and reapply something like linoleum, hardwood floors, to get rid of this odor once and for all or do I need to take all of this sub-flooring out?

If the wood dries out and should with the plastic down in the crawlspace, you may be able to get away with just sealing the floor and recarpeting.
If you can run a dehumidifier down there to keep it dry that will help to.
Another idea if you have access to the crawlspace is to pour a cement floor in there on top of a plastic barrier. That would eliminate the moisture for sure.. and I am for eliminating the source.. because I think the stink will cease if the wood finally dries.

Humidity: Cost of Keeping it Down

my workshop has some equipment that is very sensitive to moisture(humidity). during work, the temps is at 70 and RH is at 60%. This is acceptable, lower would be better. During the night(off work), I would like to save electricity so that there is no heat on. When the temps lower(outside temp is 40and RH is 95%!!) during the night(50f indoors) the RH is at around 70%. I have already tried venting the air to outside but this just causes a draft, outside air being sucked back into the shop and RH remains the same. Any ideas? I have a 40pint dehumidifier, if all else fails, I will have no choice but to use this. I want to save electricity. any ideas? Anyone know how many watts a 40pint dehumidifier uses?

Just a note that moister air takes more energy to heat than dryer air...so you may want to control the humidity more than controlling the heat.

Another suggestion is to house all the moisture sensitive equipment in a separate room ( if it is practical to the work flow process) and either heat or dehumidify just this room (or both) to maintain the conditions you require...

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Click here for our Moisture In The Home Article Click here for our Heating Tips Article Click here for our Dealing With Condensation In Your Home Article