provided by: 
1. Is there a local license, permit or some other local municipal notice that needs to be secured by the installing contractor?
2. Is there a mechanical license required for the installing HVAC contractor?
3. Has the installing contractor performed an engineering study called a heat-gain/heat-loss for your application? This is a room by room analysis of the BTU's needed for heating and cooling. A properly performed heat-gain/heat-loss is critical for success in any heating or air conditioning installation.
4. Is the installing contractor using all of his or her direct employees?
5. Is the contractor providing a certificate of insurance for liability coverage and for workmen's compensation insurance?
6. If the contractor is using other trades which are not their direct employees, are they providing certificates of insurance for non-direct employees from the respective non-direct employees companies?
7. Does the contractor have a certificate of training from the manufacturer of the heating and cooling equipment he or she is installing?
8. Has the installing contractor provided at least 3 references for you to check before proceeding with the installation?
9. Does the total installed price quoted by the contractor include applicable local, state and/or federal sales tax?
10. Is the installing contractor giving you a written, delivered performance guarantee?
11. What is the warranty on the boiler or furnace heat exchanger? Who is the warranty through - the manufacturer, the installing contractor or both?
12. What is the warranty on the compressor portion of the air conditoning/heat pump?
13. Is the installing contractor giving you a one year, unlimited warranty on both parts and labor? This means that for the first year, 7 days a week, 24 hours a day, the contractor will provide service at no charge in the event of a problem.
14. If the warranty offered is less than that stated above, has the contractor offered you the ability to purchase an extended parts and/or labor warranty?
15. If the air conditioning or heating system is being installed into a home with no pre-existing ductwork, has the installing contractor provided written guarantees regarding your ceilings, floors and walls?
16. If the old heating plant is being removed, and the new heating plant is to be vented into the same masonry chimney; then has the installing contractor recommended and/or included lining the chimney to prevent the mortar from being denigrated?
17. Is the installing contractor providing lien waivers to you from all of his suppliers on the jo efore final payment?
18. Is the installing contractor offering some form of financing? Many have "free period" terms which allow you to defer payment in part or in full for a proscribed time frame?
19. Is the installing contractor giving you a start date within 3 business days?
20. Is the installing contractor giving you at least 24 hour notice that the installation will be occurring on a specific date?
21. Is the installing contractor showing up at a specific time each day or do you have to hope they show up first thing in the morning?
22. Are you being offered all options with the equipment being installed? Do you need humidification or air cleaning?
23. Do you have some rooms that are too hot, or too cold in the wrong season? Is the contractor aware of these conditions?
24. Has the contractor provided you with a written, detailed estimate of precisely what will be done, delivered performance of the equipment being installed, and in what time frame the work will be completed?
25. In the terms of the contract, has the contractor specified the dates and criteria for when and how payment is to be made? (Provided you are not financing or taking advantage of a "free period" financing deal).
26. Are you holding back at least 1/3 of the installation contract until work is performed to your satisfaction, according to the terms and conditions of the contract?
article at HomeRenovationGuide.com