"One should never choose such a company that gives you a quotation over the phone. This is because, in case of HVAC systems it is not possible to give a quotation without proper examination. There could be two reasons as to why a company gives you a quotation over the phone. First of all, their only motive could be to win your business without giving you much facilities and secondly, they may be amateurs in this particular field. Thus, it is clear that choosing such an HVAC company is not a wise thing to do. HVAC systems are complex in nature and every unit is different from the other, so looking at each of them individually is mandatory to understand the cost that would be involved along with it. When an HVAC company tells you that their contractors have quite a few years of experience in the HVAC industry, you need to analyze it carefully. This is because in the HVAC industry, it is not enough to have many years of experience, rather it is important to be well aware of the ever changing technology that keeps coming and going in an HVAC industry. You should try to find out whether the contractors from a particular company are well-equipped to deal with the kind of unit that you have. Another important thing that one needs to keep in mind is that one should never accept anything but a written agreement from a HVAC company in terms of the expenses involved and the time that will be needed to complete the service. Last but not the least, it is recommended never to go with the lowest bidder because initially paying less might end up in a higher expenditure in the long run. "