- Check references: I can not stress this enough. If you are spending $2500 or $10,000 you must check the contractor references. A new furnace or a/c should last 20 years. But even more important is in Minnesota for example you will spend $26,000 over those 20 years on average to heat and cool your home. So ask for testimonials. If the contractor surveys there customers ask to see the surveys. If you want to make the best choice ask to talk to customer they have done work for. Make sure they will call you back on Saturday when it is -20 or 95 degrees outside if your heating or cooling doesn't work.
- Ask for copy of liability insurance certificate: Check to see what there coverage is. You want at minimum $1 million dollars coverage. Then if you really want to be safe call there insurance company to confirm there premiums are paid in full. To many companies can show a certificate but may not be late on payments. If something happens you the homeowner are responsible. If the contractor is not willing to give you this info "walk away".
- Confirm they have a current State Bond: In Minnesota for example contractors are required to have a state bond to help protect the homeowner in case the contractor goes out of business.
- Get Permits: Ask for copy of the local permit at time of installation. Note: some cities do not require permits so you can't in those cases. But call your city hall to confirm that is true.
- Back ground screened employees: Does the company criminally screen there employees. The people installing your new furnace or A/C have access to your home, make sure they are safe.
- Does the company work from home: Confirm they actually work from a office. Some contractors may office from home and do great work. But the majority of bad contractors also work from home. Don't base decision on this but it will help.
Don't worry about the brand of furnace or A/C you buy. If it is a Carrier, Goodman, Amana, Trane, Bryant, Chevy, Ford, or BMW it does not matter as much as who installs it. What matters is how well trained the installers are, will they be there for you if it fails, and will it save you money on your energy bills for the next 2 or 20 years. (BTW: no Chevy, Ford, or BMW don't make furnace and A/C)
The upfront cost of the installation will be determined by factors I listed above. Just because someone offers a lower installation you are not saving money. I have learned that lesson over the years. When the cost is lower the odds say something is missing.