When the temperature in your home is just right, you’ll feel like Goldilocks of “Three Bears” fame—not too hot and not too cold. For the air inside to stay comfortable during chilly times and on sunny days, heating and air-conditioning units must function properly. Finding a good HVAC company to maintain and repair these systems ensures all occupants stay happy—even breaking-and-entering fairy-tale children. Here are tips on finding pros, dealing with them, and the scoop on how to buy new equipment.

Our surveys of heating and air-conditioning customers revealed that some companies were rated “superior” for “overall performance” by 90 percent or more of their surveyed customers. But not all contractors are such cool characters: Several others received poor overall ratings from their surveyed customers.

We also found huge price differences. For example, to replace the ignitor for a Trane gas furnace, our undercover shoppers were quoted prices ranging from less than $250 to more than $650 among contractors in the seven metro areas where we survey consumers about service providers. To replace the dual-run capacitor for a central air conditioner, prices ranged from $125 or less to more than $500.

For new equipment, to avoid overspending get written proposals from at least three pros—some companies charge thousands more than others for the same install.

Need a new central air conditioner? Consider a heat pump instead. These devices are basically air conditioners that can both heat and cool buildings. New models are extremely energy efficient and quiet and can reduce reliance on furnaces.

For new furnace installs, you’ll have to decide whether to pay extra for more energy-efficient equipment; for example, a highly efficient 98 AFUE gas furnace costs about $1,500 more than an 80 AFUE model. But in most parts of the U.S. you’ll recoup the extra cost quickly via utility rebates and lower gas bills.

Don’t spend thousands of dollars upgrading to energy-efficient HVAC equipment without taking other steps to reduce waste. In our “Saving Energy at Home” section we detail 30 ways to cut usage. Many improvements cost little or nothing but will have big effects on your utility bills.

For installation contracts, get performance guarantees specifying how warm or cool the equipment will keep your house, and how uniform the temperature will be inside when outside temperatures reach a specified level. Be sure your contract clearly states the company’s responsibilities on issues like providing an electrical supply and hooking up your equipment to the electrical panel; providing drainage for condensate; enclosing ductwork; and painting and patching holes.