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A new AC system will typically cost you thousands of dollars, so it’s important to do your research before buying and installing one.

But while it’s important to choose the best make and model for your home — and find a price within your budget — it’s just as important to choose the best installation company for the job. The quality of an installation can impact how well your system runs, how long it lasts and how much maintenance and repairs are required throughout its life. Before hiring a contractor, vet them on more than just the price they’re offering you. Here’s what you should look for.

1. Guarantees in writing

Contractors can promise to offer you the best service, but verbal agreements can only go so far. Look for an installation company that puts satisfaction and performance guarantees in writing. Make sure it includes written estimates of how much the installation will cost, a scope of work documentation that clearly outlines what it will entail and change-order policies, which details how the company will handle work that falls outside their checklist. For instance, if they find a part of the AC system that needs replacing or low refrigerant level, a change-order policy explains how those issues will be addressed.

Before you hire a contractor, you should clearly understand (and have in writing) what equipment will be installed, how long it will take, the labor included and what happens if performance issues arise.

“If you don’t have clearly written guarantees that back up the workmanship, the system, the comfort or any problems that you may have under warranty, then all of your investment is at risk,” says Steve Wade, senior director of operations and procurement at ARS. “That’s what we like to inform our consumers, our clients: You may find somebody less expensive. Actually, it’s very likely you can find someone somewhere who’s less expensive than our company. But what you’ll do is put all of that investment at risk.”

2. Manufacturer authorization

It’s important to make sure the company you hire is authorized to sell, install and service the system you’ve purchased. Authorized companies have met certain standards and have been vetted and trained to work with the manufacturer’s equipment. They also likely have access to technical support directly from the brand and product-specific knowledge that will be necessary during the installation.

You can often find an authorized company through a manufacturer’s online dealer locator. You can look on the AC company’s website for badges, or ask them directly.

Keep in mind that just because a company is authorized doesn’t mean they’re the best for the job. There are plenty of authorized manufacturers to choose from, so be sure to also seek out references from friends and family, and read reviews.

3. Manual J load-calculation methodology

An essential part of choosing and installing an AC system is the manual J load calculation, which is a standardized method developed by the Air Conditioning Contractors of America (ACCA) that HVAC contractors can use to determine the right model for your home. It takes into account factors such as the height of your space, the number of windows and doors in your home, air leakage, which direction your home faces and how many people live in the home.

The technique helps ensure your HVAC system is the right size so it can run efficiently. Simply replacing equipment with a system of the same size or basing the size on the square footage of the area can result in systems short-cycling and having trouble keeping the space cool, plus higher utility bills.

If an installation company simply does a quick walk through to determine the AC model you should go with, consider that a red flag. Ask them if they will perform a manual J calculation before recommending a unit.

4. Workmanship warranties

Many people know to look for equipment warranties when buying new home appliances, but it's critical to ask about workmanship warranties. While a manufacturer warranty will cover the equipment, a workmanship or labor warranty covers mistakes made during installation — and they’re important. Some studies indicate that more than 65% of residential HVAC systems haven’t been installed properly.

Before working with an AC installation company, ask how long their workmanship warranty lasts and about any other extended labor coverage options.

5. Post-installation support

Once your AC system has been installed, you don’t want to be left hanging if any issues come up. Look for a company that offers post-installation support such as start-up testing to make sure the system is running efficiently and commissioning, which is a quality-assurance process.

You should also ask about maintenance plans — and what you need to do on your own, such as change air filters — plus whether the company offers emergency support. You can also ask about their warranty services so you’re prepared should your AC break down.