Cooling in the data centre - BTU emissions per server

We are currently in the process of replacing our air conditioners for our server room.

To ensure we get the right level of cooling, we need to know the amount of heat our servers are generating.

We have up to 100 DELL servers in racks plus a number of other test machines about the place (we have a row of racks, plus a few tables with test servers on/under them). So I've been looking for a list of DELL servers which details the amount of heat (BTU/Hr) they emit.

I found the dell rack advisor tool but it appears to have been replaced by the
DELL data centre capacity planner

I also found another tool from APC:
http://www.apc.com/tools/ups_selector/index.cfm

I've also been looking at the dell documentation for each server as there is sometimes a 'power' section which details BTU or Watts emitted.

Some of these tools will display a BTU/Hr figure (which seems to be the industry standard of measuring heat output in a data centre?) whilst others will display amps or watts etc.

1 BTU = 3.4 watts (I think its 3.412 to be precise)

Lets use an example:

DELL Poweredge 2600

DELL Datacentre Capactiy Planner:
Watts: 602
BTU/Hr: 2047 (602*3.4)

DELL Documentation for the 2600:
http://support.dell.com/support/edocs/systems/pe2600/en/index.htm
Then in the "Service Manual" -> "Technical Specs" it has a section called Power - which lists:
Heat dissipation: 3100 BTU/Hr
Watts: 730

APC Selector tool:
Watts: 376
BTU/Hr: 1284

As you can see, the BTU from the 3 sources ive found are quite different. Plus, not every DELL server is available with the different tools.. and sometimes the DELL documentation doesnt include a power section at all!

So im scratching my head a bit.. We are using APC racks and APC have told us to use their tool.
Ive rung DELL and theyve suggested using the DELL docco for each individual server.
Then I found DELLS datacentre capacity planner which is totally different again.

Has anyone gone through the task of listing the heat emissions for their servers? What process did you follow? Have you got any suggestions?

Thanks!
Dave