How do you seal a vertical window air conditioner?

Installing a vertical window AC comes with sealing any gaps between the window frame and the unit with insulation foam to prevent possible air leaks.

Window air conditioners are installed through a window opening in a room you want to cool down. Not all windows are the same, however, some require a specific vertical window air conditioner to be installed correctly in a vertical or casement sliding window.

Installing a vertical or any other window unit requires that it be properly sealed in order for the unit to work efficiently. Sealing the unit protects it from any air leaks, but how should a vertical window air conditioner be sealed to protect it from harsh weather conditions and other possible issues?

Sealing vertical window air conditioners

Some air conditioning systems require an added layer of protection from interference with its cooling and heating abilities.

This is why any air conditioning system must be properly installed and sealed around the unit where gaps may pose a risk of air leaking inside or out, causing the unit to overwork to compensate.

Window air conditioners, particularly, need to be correctly sealed to prevent gaps between the unit and the window where air could enter and escape between the indoors and outdoors.

How do you seal a vertical window air conditioner?

Vertical window air conditioners are not like standard window units as they are designed to fit into narrower, vertical window openings.

These windows slide up and down or side to side. The trick to avoiding having a lot of work to do to seal the unit is to find the right sized unit with minimal gaps between the window frame and the window air conditioner.

However, even with the right size, you will still need to seal your vertical window air conditioner after you have installed the unit into the window opening and it has been solidified securely.

In order to seal the vertical window air conditioner, you need to use a window air conditioner foam insulating strip or foam weather strip which closes off any gaps that can be air leaks.

This window foam seals between the windowpane and glass around the body of the window unit and needs to be inserted as such. Some units come with the insulating foam strip while, for others, you have to purchase them yourself.

Amazon has some affordable, durable insulating foam strips you can purchase.

Insulation tools Description Amazon price
YIJUHOU foam seal

Buy it on Amazon
·   High-resilience flexible weatherstrip seal

·   Strong self-adhesive

·   Easy to customise, cut, and bend

Yotache foam seal

Buy it on Amazon
·   Strong adhesive backing that is waterproof

·   Highly resilient to compression and deformation

·   Superior weather resilience

Magzo foam seal

Buy it on Amazon
·   inch thick

·   Multifunction open cell foam for wide use, not just insulation

·   High-resilient weather stripping


Another option for sealing your vertical window air conditioner

The top of the vertical window air conditioner is usually the one place where there is a gap between the unit and the top of the window.

To seal this, you can use plywood. It needs to be cut to the same size of the gap and sealed.

Where there still might be small gaps, insulating foam can be used again, as long as the air conditioner has no gaps between it and the window frame or between the glass panes of the upper and lower sashes.

Consulting manufacturer insulation guidelines

Following the insulation guidelines that the air conditioner manufacturer has provided can also help you ensure you have sealed your vertical window unit properly.

Before you proceed to seal your window unit, carefully read and follow these guidelines to ensure you are doing the job properly.

If you do not feel confident enough to do it yourself, it is a better idea to have an HVAC professional do it for you, that way you can avoid doing something wrong and dealing with a malfunctioning air conditioner later.

Is it possible to install a standard window AC to a vertical casement or sliding window?

It is not really recommended that you fit a regular window unit into a casement window, but if you really need to, then some handiwork will be necessary.

A wooden frame needs to be constructed to fit the opening and the unit needs to be supported by either a board or metal bar across the top rail opening.

When the window is closed against the unit, the opening above must be closed with glass or plexiglass and gaps must be sealed with foam strips.

Leave a Comment