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Thermo Twin | Frequently Asked Questions

Frequently Asked Questions


What is Condensation?

Is your glass “sweating” – is water beading or ice forming on the inside surface of your windows?  Don’t be too quick to blame the windows!  There’s a good chance that what you are seeing is condensation, a sign that there is excess humidity in your home.  Humidity, water vapor mixed with air, is drawn to the coolest surfaces, such as your window. Cool air cannot hold as much moisture as warm air, so windows and doors often collect this moisture and make it visible. A surface that is cooler than room temperature is more likely to show condensation.

What Causes Condensation?

Indoor moisture is caused by a variety of factors, including cooking, showering, running dishwashers, storing firewood, pets, fish tanks, plants, clothes dryers that are not vented properly, even breathing. Your new windows are most likely showing condensation more than your old ones because they are more air-tight – less air is entering your home from the outside. The air leaking from older windows evaporated the moisture before it could collect.  While some humidity is necessary for health and comfort, chronic and excessive condensation should be tipping you off to take some action before serious, costly damage, such as decay, mold, paint problems, and even major structural damage occur.

Temporary Condensation

There are several ways to tell if the condensation on your windows is temporary. Does condensation typically form:

  • During baths or showers, cooking, dishwashing, laundry, or other steam-producing occasions?

  • During the start of each heating season? Houses absorb moisture during humid summers, and will dry out after a few weeks of heating.

  • During sharp temperature changes? Sudden drops in temperature, especially during the heating season, can create temporary condensation.

  • During new construction or remodeling? Building materials contain a great deal of moisture. When the heat is turned on, this moisture will flow into the air inside the home. It usually will disappear after the first heating season.

Problem Condensation

Excess moisture in your home may eventually cause problems. It may be time for action if you notice the following signs in your house:

  • Condensation remains on windows throughout the day, even when the outside temperature has warmed up.
  • Condensation is forming and running down the walls. It may also be causing discoloration, staining, peeling wall paper, and blistering paint.
  • The air smells musty – this could indicate mold, mildew, or in the worst cases, rot – or odors from everyday activities that linger too long. Odors increase in intensity with high relative humidity.
  • Mold, mildew, and/or rot is visible. Mold and mildew thrive in moist areas and can cause health and house damage.

Interior Condensation

Interior condensation forms on the inside pane of the glass within your home. This is the type of condensation most homeowners notice and become concerned about. It usually forms in the winter, especially at the beginning of the heating season. As the outside temperature drops, the inside surface will also get cooler; therefore, condensation will form at lower relative humidity on cold days. The colder the air outside, the more likely condensation is to occur. The good news is you have a great deal of control over interior condensation.

Exterior Condensation

Conversely, exterior condensation, which forms on the outside pane of the window, typically occurs in summer. This type of condensation can occur for several reasons: the glass temperature drops below the dew point temperature of the outside air, no air movement, there is a high relative humidity, there is a clear night sky, or there are plants located near your window.  Exterior condensation should not concern you, since it usually evaporates as the day wears on and will not affect the interior of your home. Since you cannot control the relative humidity outside your home, the only step you can take to combat exterior condensation is to warm the inside surface of the window, as this is a way to warm the outside surface. Seeing exterior condensation on those rare days should be a reassurance that your windows are doing their job: keeping your heating and cooling in your home where it belongs, and saving you money.

Condensation and Health

Improper temperature and humidity can cause comfort and health concerns. Warm, humid environments encourage the growth of molds and fungi which can lead to allergic reactions. Dry environments can irritate sinus linings and can progress to a sinus infection. The best way to combat this is to achieve the appropriate balance of temperature and moisture in your home.

Acceptable Ranges of Temperature and Relative Humidity During Winter

The humidity level that should be maintained in your home during the winter varies with the outside temperature. The colder it is outside, the lower the humidity level must be inside your home. All major manufacturers of humidifiers list the recommended humidity settings based on outside temperatures. The charted guideline is recommended by every major manufacturer of windows and humidifiers.




-20° F

15% or less

-10° F

15% - 20%

0° F

20% - 25%

+10° F

25% - 30%



Climate and Other Factors

Areas where the temperature average for January is 35° F or colder tend to have more occurrences of condensation. The greater the extremes between outdoor and indoor temperatures, the more likely moisture will become visible on your windows.

Bay, bow and garden windows often create opportunities for condensation to show because air circulation is frequently limited, and their projection from the insulated house wall generally makes them a few degrees cooler. Heavy draperies, blinds, and other restrictive window treatments also limit air flow and increase the likelihood of condensation.

Reducing Condensation

Now that you know the what and why of condensation, it’s time to learn how to reduce the conditions that cause it, especially if you are concerned about the effects of that excess moisture on your home and health. There are several steps you can take in three main areas:

  1. Reduce Moisture Sources
    1. Stop or severely limit the use of humidifiers, or adjust them to the appropriate setting (see page 3).
    2. Run a dehumidifier if needed.
    3. Limit plants, aquariums, and pets. If you care for a lot of plants, group them in one sunny room and avoid overwatering.
    4. Inspect your gas appliances. Malfunctioning gas appliances can deliver excessive water vapor into the air along with more dangerous contaminants. Be sure you have a carbon monoxide alarm.
    5. Store firewood outside.
    6. Eliminate plumbing leaks.
    7. Do not air-dry clothes indoors  
  2. Increase Ventilation
    1. Open windows for a few minutes each day, particularly after steam-producing activities such as showering/bathing, laundry, and cooking. Heat loss will be minimal.
    2. Run kitchen, bathroom, and other fans longer and more often.
    3. Improve or add a ventilation system in your home through attic, roof and soffit venting. Ensure that everything vents to the outside.
    4. Make sure crawl spaces are properly ventilated and attic louvers remain open all year.
    5. Open blinds and drapes. Heavy window coverings restrict the flow of warm air over the interior glass surface.
    6. Operate ceiling fans to improve air circulation.
  3. Increase Air Temperature
  4. Raise the temperature inside the house.
  5. Direct warm-air supply ducts toward windows or even use a fan for increased air circulation at windows.

If you continue to have alarming condensation and other moisture problems and you have taken the steps above, it may be beneficial to consult a heating contractor specialist for further cures.


Is Thermo-Twin Energy Star certified?

Yes! Thermo-Twin products are Energy Star certified as a reflection of our quality and dedication to environmental friendliness. Energy Star certified windows help to decrease household energy bills up to 10 percent. Reduced energy consumption means decreased greenhouse gas emissions and a smaller carbon footprint from your home.

What is Super Spacer®?

Super Spacer® is a unique space-aged technology by Quanex that Thermo-Twin incorporates into all of our window products. These spacers help to provide better insulation and increase the energy efficiency of each of our window products. Learn More

What is virgin vinyl? Why is it unique?

Virgin vinyl is what Thermo-Twin uses in all of our vinyl window products. The material is unique in that it is 100% new vinyl, as opposed to recycled, which improves the stability of our window products and consistency in quality.

What are double hung windows?

Double hung windows are similar to single hung in that they have two individual sashes. However, double hung windows are unique in that both sashes move up and down and tilt to allow for easier cleaning. Learn More

What are wood-clad windows?

Our wood clad window products incorporate the beauty and durability of western pine wood in the jambs, sashes and trim. Just like our other windows, wood clad products incorporate Super Spacer technology and are available in a number of styles, from double hung to casement or picture windows.

Can you tell me anything about aluminum windows?

Thermo-Twin offers a wide range of aluminum window products, in styles ranging from awning to casement or picture windows. Aluminum windows are especially durable, making them ideal for practically any location, like residential or office use. Our aluminum products come with Super Spacer technology designed to enhance energy efficiency and may be ordered in white or dark bronze color configurations. Learn More

Does Thermo-Twin provide window installation services?

Of course! Not only does Thermo-Twin design, manufacture and deliver each of our windows; our professional installers will come to your home for custom installation. We take the greatest care in handling our products and use caution to protect your home and possessions during the installation process.

What is NFRC? Why is it so important that Thermo-Twin windows are NFRC certified?

The National Fenestration Rating Council (NFRC) is dedicated to quality home finishings. At Thermo-Twin, we diligently oversee the manufacturing process and quality check each window that comes through the assembly line for chips, cracks, scratches and overall product durability. The NFRC label on our windows is our guarantee that you are receiving the best products possible.

Do you provide products other than windows? If so, what other products do your specialize in?

Yes we do! We also sell entrance and sliding glass doors, vinyl home siding and we build custom sunrooms!

Do you make your own door products?

We partner with Provia Door, working together to provide you with high quality, energy efficient entrance and sliding doors. Each steel or fiber glass door we sell and install is Energy Star certified, foam-filled and is weather sealed for thermal efficiency.

What can you tell me about your entrance door products?

Our standard and custom entrance doors are made with beauty, durability, security and energy efficiency in mind. We aim to both beautify and protect your home.

What is unique about your sliding glass doors?

Each of our sliding glass door products is manufactured with energy efficiency in mind, constructed with weather stripping on both panels and incorporating Super-Spacer technology. Learn More

Are your doors standard-sized or custom?

At Thermo-Twin, we create and sell both standard and custom doors to fit your needs. Designs can both be tailored to your individual style and cut to fit your home’s doorway.

What kinds of sunroom options does Thermo-Twin offer?

We specialize in three different custom sunroom options: year-round, seasonal and patio cover sunrooms. Why let the weather get in your way when you can enjoy the outdoors all year? Learn More

Why should I get a year-round sunroom?

Year-round sunrooms let beautiful light into your home all year, without compromising the temperature of your home. We offer gable, studio and existing roof styles.

Can you tell me a bit about seasonal sunrooms?

Seasonal sunrooms function as extra living space in your home, but not all year round. Spending time in your seasonal sunroom is ideal during mild weather, rather than the heat of summer or the coldest winter days. Our seasonal sunrooms are available in various colors and may feature different screen types, like aluminum-framed or fiberglass.

What if I just want a patio cover?

Thermo-Twin can design and install a custom patio cover for your home. Built on top of your existing patio, screened-in patio covers let you enjoy the outdoors without putting you within reach of pesky insects or strong UV rays.

How do I get in touch with Thermo-Twin about my project?

For a free estimate, feel free to complete the form on our website. You may also call 800-641-2211 to discuss your needs, ideas and associated costs.

I need to reside my home. Can you do that?

Of course we can. Thermo-Twin provides durable vinyl siding options for any home, from a classic remodel to new construction. Vinyl siding stands the test of time because it doesn’t split, crack or require repainting. Our proprietary designs deliver outstanding durability, rigidity and wind resistance.

I have an old home. Do have need to be concerned about lead paint?

Lead paint may be hazardous if not handled properly. However, Thermo-Twin is a lead-certified renovation firm and our professional window installers are trained to safely work around and/or remove lead products during your renovation.

Where are your offices located?

Thermo-Twin has four locations in Pennsylvania, Ohio and New York! Get directions to our offices online so we can meet and discuss your needs.  Open hours are Monday - Friday 8:00AM to 4:00PM.  Please call us during the holidays to verify open times.

I want Thermo-Twin to help with my window installation. What are my next steps?

We make the process of choosing and buying windows simple. You will be on your way towards having gorgeous new windows for your home in just a few steps.

  1. To begin the process, give us a call at 1-800-641-2211 to discuss the scope of your project.
  2. We’ll arrange for a sales representative to come to your home to chat in-depth about your needs and to help you choose your ideal window products.
  3. Next, we’ll do a rough measure, followed by a final measure of your window spaces to determine the proper size and shape.
  4. We’ll work with you to arrange the logistics of your window installation and choose an installation date.
  5. Our team will install your energy efficient windows, keeping the cleanliness and safety of your home in mind, and we’ll clean up before we go.

How do I become a wholesaler?

To become a wholesaler, visit our wholesale page. Here you may register to become one of our wholesale partners and learn about the benefits of partnering with us!