Question

Our aluminum-frame windows are harboring condensation and mold. Can you recommend window solutions for a damp environment?

Asked by Norm Milstein

I live in a townhouse near the water. The windows are double-paned and fairly low quality, with aluminum frames. As we live in a damp, foggy area, the windows that don't get much solar exposure tend to condense water on the inside, which results in mold growth. I think the aluminum frames contribute to this problem by conducting heat away. Would it make sense to replace (or perhaps retrofit) the windows in the shadier areas of our townhouse? If so, what windows would be likely to do the best job for us given our damp location?

Answer

Steve Saunders

Answered by Steve Saunders

Irving, TX

TexEnergy Solutions, Inc

January 15, 2010

Condensation on windows is a common and frustrating situation. Fortunately, you have a lot of options for addressing this problem. 

The condensation is caused by a combination of high humidity and a less-than-great window. Aluminum windows have a high U-value. This means they transfer heat well. If it gets cool outside, indoor heat escapes through the metal frame of the window. Often the aluminum frame becomes colder than the dew point of the water in the air. The warmer the air, the more moisture it can retain. When warm air comes in contact with the cold window frame or the cold glass surface, the air is cooled and moisture is released, causing droplets to condense on the window and window frame. The water eventually pools at the bottom of the window, where it can lead to mold growth. 

Regardless of the location of the condensation (frame or glass), there are a variety of ways to address this problem.  

  • Replace the entire window. You may want to make the change from highly conductive metal frames to thermally broken frames or frames with a lower U-value. A lower U-value means the frame resists the transmission of temperature and is less susceptible to condensation. Less heat-conductive framing materials, such as wood or vinyl, are good choices to reduce the formation of condensation. 
  • Replace the glass. You may choose to keep the frame and replace the glass. You would want to choose energy-efficient low-e (low emissivity) coatings, or glass with wood or vinyl spacers between the dual panes. 
  • Dehumidify. You may want to consider a whole-house or in-room dehumidifier to lower humidity. Moist air in the home is coming in contact with the cold window frame or cold glass surface, and when the air cools it releases moisture onto these surfaces. As you reduce the moisture content of the air, you reduce the relative humidity and make the glass less susceptible to condensation. 

All the choices have merit and each has a specific cost-benefit relationship. Let's address the relative costs and benefits of each possibility. 

Replace the entire window

New windows offer an exciting prospect for a new outlook on the world. Vinyl windows have improved dramatically in recent years, and I have become a believer that today's vinyl is a durable product. Wood windows can be wonderful—adding warmth and class to the interior and exterior of your home. The maximum benefit will come from choosing a high-quality window with a lower U-value frame and double or triple panes (with a low-e coating). A new window would likely reduce or eliminate condensation so that the mold problem would disappear. Other benefits are likely to follow. I bet the seals are broken on your current windows, causing the glass to look fuzzy or dirty. Improved windows will enhance the tightness of your home's "envelope." The window panes will be sealed, so the view out the window will improve. There could also be a slight reduction in energy usage. 

However, I am not certain that the benefits outweigh the costs, and there are some potential pitfalls to think about when replacing windows. 

Windows have a huge range of installed costs. Vinyl windows are generally less expensive than wood. The installed cost of windows can range from $500 per window to literally several thousand dollars per window. You will want to find replacement frames that match the color of the original frames as closely as possible to give your home an integrated look. Another major consideration is how the windows are installed. The best methods involve removing the siding or brick from around the window and installing proper flashing. The purpose of the flashing is to ensure that the water that comes down the drainage plane (behind the exterior wall of your home) is pushed to the sides of the window, continues down the wall, and finally kicks away from your home at the bottom of the wall. The key is to keep bulk moisture (water droplets) from getting into your wall cavity, where it can pool and cause mold. Yes, the biggest potential risk in replacement of windows is that the walls may not be properly flashed and you may eventually wind up with water damage. 

The financial and aesthetic cost of removal and replacement of the brick or siding from around your windows can be substantial. Most replacement installations are window-for-window only and the exterior of the home is not impacted. Replacing the window and using caulk as a barrier is so much less expensive that the vast majority of window replacements follow this method. A good installation will include some focus on pushing water away from the window, and lots of 20-year caulk will be utilized to reinforce the ability of the replaced window to repel water. I have concerns as to the durability of window replacement in the long term (meaning more than 20 years). 

The best environmental choice of frame material is another interesting question. In some ways it is like going to the grocery store and choosing between paper and plastic bags. Paper represents the wood frame, which is produced from a renewable resource. Plastic represents a vinyl window, which could be considered an alternative to cutting down our forests. You can frame the debate in a way that favors either argument: both could be good, both could be bad. Many (and I suspect most) homeowners let cost be the deciding factor and choose vinyl over wood. 

Replace the glass

This could be a good decision if the majority of the condensation is caused by the glass and not by the window frame. Key benefits to this choice are less condensation on the window, improved sight lines because the replacement glass will have the seals intact, and avoidance of risks related to changing the flashing on the window frames. You may need to closely examine your current windows. If a significant percentage of the condensation comes from the window frame, replacing the glass may not be the best solution. 

This option would likely cost less than wood windows but may not be less expensive than vinyl windows. This is a much less common choice than replacement of windows and the work requires a high level of skill from the glazier to properly match the size and installation characteristics of the windows to be replaced. These glaziers are not the easiest to find, and they will need to visit your home more than once for measurement and installation. Installation of window glass will likely cost $300 and up per window, depending on size, location, and ease of access for installation, among other factors. 

Dehumidify 

This is my favorite idea for quickly getting some traction on your problem with a low-cost solution. This is an "end around" your condensation problem. Remove the humidity from the air and it is more difficult for the water to condense and puddle on your windowsill. 

A test is very simple. You can go online or to your local hardware store and find an inexpensive "in-room" dehumidifier. These start at under $300. You may find that the dehumidifier quickly addresses your concerns, and if so, it is such a simple and quick fix. From your posting, it sounds as if you may have more than one room that is affected. You can start by trying it in one room to see if works. If the experiment is successful, you may decide to invest in multiple dehumidifiers. 

Since you live near the water, you might consider installing a whole-house dehumidifier. This, like window replacement, is a job for a professional. You can purchase a whole-house dehumidifier through a quality HVAC contractor in your neighborhood. Depending on the product you choose and the complexity of tying the product into your existing mechanical and drainage systems, the installed cost could range from $1,800 to $3,500. There are other significant benefits to a whole-house system. The system will lower the humidity in your home and keep it low all the time. The window condensation problem will be eliminated or reduced to such a low level that it no longer creates a mold problem. Your summer comfort may also increase with less humidity and at higher temperature settings on your thermostat. More comfort at higher temperatures generally results in lower electricity bills for air conditioning. I like the dehumidifiers listed in the resources section at the bottom of this article. 

Summary 

For all three options, the range of costs begins at minimal and could get very expensive. Given the fact that the problem seems to be concentrated in certain parts of the house, I would try the in-room dehumidifier first. This is quick, cheap, and easily actionable. At the end of a month, you have a pretty good basis to evaluate your potential next steps. If the condensation problem is dramatically reduced, you may have the answer. If more work is needed, then you can think about which of the other options makes the most sense to you. 

In my own home, I have tried or considered each of the options I recommend to you. I have replaced metal-framed windows in my home with vinyl windows. I did not remove the siding because it would have been prohibitively expensive. I made the trade-off for what I wanted now, and I may or may not have a problem in 20 years. 

We are considering the replacement of panes on the eastern side of our home. This will make the hot Texas summer mornings more comfortable because the low-emissivity coating will reflect UV rays and keep the rooms at a temperature more consistent with the rest of the home. We are not planning on changing out the remaining metal window frames because we can resolve our concerns without adding the risk of water intrusion around a window that is not properly flashed. 

In addition, we recently had temperature and humidity recorders at our home. We were testing the change in humidity levels in the home at different times of day. It does appear that a dehumidifier could have a positive impact on the average relative humidity in our home, and we are likely to add a whole-house system by next summer. 

There are many choices and you are only limited by your imagination and your budget. Good luck with your project. 

Room Dehumidifiers

Good: Comfort-Aire 501 and 651 low-temperature electronic dehumidifiers; $319.95 and $349.95 respectively 

Better: Delonghi DE650P 65-pint low-temperature dehumidifier with built-in condensate pump; $399.95 regular, $299.95 on sale 

Best: Santa Fe Dehumidifier (Classic); $1,385 

Whole-house Dehumidifiers

(Note: Whole-house dehumidifiers require professional installation. It is generally best to purchase this type of item through the HVAC service company you normally use for repairs and maintenance on your system.) 

Good: Aprilaire Dehumidifier Model 1750A; $1,349 

Better: Comfort-Aire WHD-130A Whole House Dehumidifier; $1,265 

Best: Santa Fe Rx; $1,885

Tagged In: mold removal

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