Chris R.

Have a look at some of the full spectrum solutions like NetSuite - as suggested previously, cloud based solutions are great cost effective, scalable options that have a good ecosystem of natively integrated ISVs if the native functionality is lacking (e.g. Payroll/HR from InfinetCloud or quoting/proposal management from Webcom). 

While it's not specifically written for heating equipment, have a look at Webcom's Websource CPQ solution.  It has both a quick quote and robust product configurator that would likely handle the need.