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What Do Windows Have to Do With It? All About Windows and Your HVAC?

In this article, we address why windows are so crucial to your HVAC, including load calculations, how they impact heating and cooling, and what to ask for from your contractor.

What Do Windows Have to Do With It? All About Windows and Your HVAC?

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Olivia Minnier


July 15th, 2022

When you think of the windows in your home, you picture the ability they give you to add ambiance and comfort to your home, a view into the outside, safety, or many other things. Your HVAC system probably doesn’t come to mind. But maybe it should.

The windows in your home play more of a role in your HVAC system and overall comfort than you might think. A good HVAC company or salesperson will utilize the number of windows you have for a load calculation to choose a system.

What is a Manual J-Load Calculation?

In the simplest terms, a Manual J Load Calculation is a series of measurements that include different parameters of your home. Both the Air Conditioning Contractors of America (ACCA) and the Department of Energy state that your HVAC contractor should perform this calculation.

This is not just the square footage of a home. But unfortunately, square footage alone was the old way of doing things, and some still subscribe to it.

There’s an industry joke that contractors used to stand on the curb outside a home and put a finger out in front of them. If the finger covered the home, it needed a one-ton load in its HVAC equipment. Two fingers, two tons, and so on.

While this particular story is likely out of date now, it is pertinent to keep in mind that some contractors cut corners in the process. Whatever contractor you choose, make sure your estimate includes a full load calculation.

But how does this include the windows of my home? Well, actually quite a lot.

How Do My Windows Impact a Manual J-Load Calculation?

The number of windows you have in your home, the direction they are facing, and what they are made out of all are factored into your Manual J Load Calculation. Therefore, they significantly impact the size and type of system that can be chosen for your home.

Other factors are taken into account during a manual J-Load Calculation, such as:

  • The insulation value of the siding on a home
  • How recently insulation was blown into the attic
  • How many windows does a house have
  • The state of the windows (single-pane, double-pane, etc.)
  • The number and type of doors
  • Square footage (total)
  • Square footage of the floor over the crawl space
  • Square footage of the floor over the basement
  • The number of people living in the home
  • Allowances for heat added in the kitchen and bathrooms
  • Rooms that lack ductwork but need heating/cooling
  • Height of the ceilings
  • Whether the house has a basement or is on a slab

Many homes have unique features that require additional calculations or measurements. Therefore, the list above is representative of common aspects of the calculation but does not include all of them.

In addition to playing a large part in choosing the proper size and type of HVAC for your home, windows also impact the efficiency of your system. From sealing your windows to the variety of window coverings, you have to look at both interior and exterior window treatments, they can all impact your efficiency a lot. A good contractor can handle all of these steps for you

Sealing Your Windows Makes an Impact on HVAC Efficiency

Making sure your windows are correctly sealed is the first step in improving your efficiency. Windows are a significant source of energy loss and energy efficiency. Approximately 25% to 30% of residential heating/cooling energy use can be attributed to window performance, according to

The glass itself has sealing properties that can help keep the air in from your HVAC, but if your windows are not insulated properly, it can lead to:

  • Humidity sitting inside your home
  • Reduced Heating Efficiency
  • Poor Cooling efficiency
  • Drafts

Humidity Sitting in Your Home

When humidity gets inside your home, it can make it very uncomfortable. Especially in the summer months, when the air from outside is overly sticky, it can create problems if it gets inside your home. HVAC systems reduce humidity, but if there’s a perpetual influx of air coming in from the outside, your system will have to keep working harder to keep humidity levels down.

This can lead to higher energy bills and increased mold, dust, and allergens inside your home.

Ideally, your home humidity level should be between 30%-60% for all seasons. Having a proper window seal can ensure you keep it at that level or close at all times of the year.

Reduced Heating and Cooling Efficiency

As you may have guessed, having improperly sealed windows can also lead to reduced heating and cooling efficiency as well. Just like keeping your home's humidity at an ideal level, your HVAC will work harder to maintain the heat level inside of your home. In addition, some of the air that is supposed to be heating your home or cooling it down will just leak out, causing not only inefficiency but a money loss as well.

Drafts Inside the Home

Lastly, drafts can also occur if your windows are not sealed properly. Again, these will cause your machine to work harder and for more air to escape.

However, you can take precautions and make sure your windows are adequately sealed and effectively.

Effective Methods of Sealing Your Windows for HVAC Efficiency

There are several methods you can use to better seal your windows or areas around your windows to increase your HVAC efficiency and save you money in the process. These include:

  • Caulking
  • Weatherstripping
  • Bubble Wrap


Caulking is a sealant used to fill joints and is an effective way to repair any areas around windows that could be leaking air. You can find caulking at most home improvement stores for about $3.


Weatherstripping is another effective method of sealing any cracks or seals. Weatherstripping is made of vinyl, foam, or silicone and is weather resistant. Weatherstripping is also affordable and available for around $7 for a roll.

Bubble Wrap

In a pinch, you can also use bubble wrap to seal off your windows. Spray water onto the window first & the bubble wrap will stick to it and act as a second glass layer. Bubble wrap is also relatively affordable and available for around $10 a roll.

Window Coverings Can Help With HVAC Efficiency

Interior and exterior window coverings can play a role in your HVAC. Pleated shades provide plenty of cover for windows and are the most efficient way to cover windows. The air in between the pleats acts as insulation. Drapes are also good at blocking out light and boosting energy efficiency. You can add an energy-efficient thermal layer to your drapes or get specific drapes designed to be energy efficient.

These curtains are relatively inexpensive and run about $9-$12. Whereas the light filtering self-install shades run slightly more expensive at around $19.

There are also window treatments you can add to your windows to increase efficiency.

Window Screens

Adding screens to your windows can also help with energy efficiency and help you get the most out of your HVAC. Screens can be installed onto your windows to assist with UV rays, damage, glare, and solar heat gain inside your home.

Interior and Exterior Reflective Windows Treatments

If your home has many windows facing the sun during the day, you can also try applying a reflective window film to them. You can either do this yourself or have someone install it on your windows.

These products can help with energy efficiency as the light bounces off the film and away from your house, reducing the light and heat that your home attracts. Think of it like a pair of reflective sunglasses for your home’s windows. An added benefit of these products is that they typically provide a tint to your windows that creates an added layer of privacy protection.

This is also an affordable option for custom size windows or accent windows that you either don’t want to cover, have a hard time finding coverings for, or don’t want to pay the cost of having blinds, shutters, or screens installed.

Don’t Wait to Help Improve Your HVAC Efficiency

At Fire & Ice, we understand how complex your HVAC system is and how important it is to ensure your system is running efficiently. If you have any questions about how sealing or improving your windows can help your HVAC efficiency, feel free to call us. If you live in the Central Ohio area and are ready to take the next step towards improving your HVAC, use the zip code map to see if you are in our service area.

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