This can be quite the task. A quick Google search will reveal a number of Heating and cooling companies within .004 seconds. Reference this checklist to assure you are dealing with a quality company.
Ask the people that you surround yourself with who they have used in the past or present. Online reviews can only tell you so much. However, your social circle will offer the best reference possible.
Don't be afraid to ask contractors for their contractors licence, mechanic information, WSIB certificate and liability insurance. Most companies will have this ready in an instant. Any pushback and you may want to reconsider. All work done in your home can be your liability, if the contractor doesn't have the appropriate coverage.
Assure that the installer/service person is an employee of the company that you purchase the product from. This will assure that the installation will comply with the company standards and the employee is directly responsible to answer to any defect in workmanship. Location of your contractor is important for long-term service and ask for 24 Hour service.
Creature Comforts belong to the BBB (Better Business Bureau), HRAI (Heating Refrigeration Air Conditioning Institute) and the Burlington Chamber of Commerce to name a few. Other companies may belong to other groups which indicate that they are active in the industry to restore quality installations and overall work practices. Owners and staff invested in the community is often an indication of pride within the company.
Estimates/quotes should never be entertained unless a sales representative has viewed the project. Every project is different and you don't want to enter a contract with someone that keeps adding additional charges after the work has started. Get a written bid/estimate up front. Reliable contractors are professional, prompt and courteous. How a company treats you now reflects on how they will treat you in the future.