Estimate heat produced in a server room?

Is there an easy way to generally estimate the amount of heat generated by all the equipment in a server room?
We are moving to a new space and we have 8 servers, a PBX, an AS/400, 6 Cisco switches, and a UPS going into a server room approx. 20 x15.
The A/C guy has asked for a load in BTUs. How do I calculate this?