Installing a patio door costs $600 to $6,000 on average for the new door and installation labor. Replacements cost slightly more at $700 to $6,500, which includes an extra $100 to $500 to remove and dispose of the old doors. There are several types of patio doors to choose from, the most common being French doors and sliding glass doors.

• French doors cost $1,300 to $5,500 installed on average for exterior patio doors. French doors are a classic and popular choice for patio doors due to the large amount of natural light they let into a space. They're typically made up of one or more panels of glass, installed as a pair, and open from the middle.
• Sliding glass doors cost $1,200 to $4,000 installed, depending on the size, the type of glass, the frame material, and the number of panels. Sliding doors are among the most common type of doors homeowners use for patios.
• Bifold patio doors cost $5,000 to $20,000 with installation and feature panels, typically glass, that fold like an accordion along a track, creating a much more open space than other types of patio doors. Their premium price point, however, makes them a less common choice.

There are several signs to watch out for that indicate it's probably time to replace your current patio door or sliding doors. Consider replacing them if:

• The door is old and feels drafty.
• The door leaks when it rains, or you notice condensation.
• The door makes squeaking or scraping sounds.
• The door sticks when opening.
• The door glass is cracked or shattered.

Most patio doors last 20 to 30 years on average, provided they are properly cared for. The door's exact lifespan depends on several factors, such as the material it's made of, whether and how much it's exposed to the sun, and how much use it gets that contributes to the wear and tear over time. 

Patio door installation or replacement types about 3 to 6 hours in most cases. This includes removing the existing door, making any necessary repairs, and installing the new door. Depending on the door's size, type, and the structure of the surrounding wall, some installations can take up to a full day.

Follow these guidelines to help you choose a qualified company for your patio door installation:

• Compare 3 to 5 estimates from door installers who have been in business for several years.
• Hire a patio door installer who is licensed, bonded, insured, and has high customer ratings on HomeGuide and Google.
• Get a written contract and warranty in hand before any work begins.
• Avoid going with the cheapest patio door quote as it may signal inferior quality work.
• Don't pay in full until the installation is complete.

Asking the right questions can help you choose the best installer for your budget and needs. Start with these:

• Are you licensed, insured, and bonded?
• How long have you been installing patio doors in this area?
• Can you offer a free in-person estimate to ensure the quote is accurate?
• Will you provide a breakdown of everything the estimate includes?
• What type of patio door do you recommend for this space, and why?
• How long do you think the installation will take, and how soon can you schedule it?
• Does the estimate include removing and disposing of the old door, as well as all cleanup afterwards?
• What additional costs might come up during an installation like this one?
• Do you offer a guarantee or warranty? If so, for how long?