HVAC industry inventory

Hi All, 

Wondering if there are any HVAC companies who do 24hr service and how they manage their inventory. We are currently using FIFO which I have looked into and is not recommended for industries like HVAC. Another thing we are currently doing is adding every single part into our system, which is creating way to much inventory. How can we tag items for service repairs on invoices without ever adding them to our inventory? Preferebly without creating a job but if that's what needs to be done then so be it!

Any information or comments will help!