Is there a general rule for calculating heat dissipation in electronic equipment if it's not listed in the specs?
I have a couple of projects coming I'm working on that require this. For one situation I need to provide the heat dissipated for some routers, switches, UPSs, and two-way radio repeaters I'm installing in leased rack space in a equipment room.
I also have a situation where I need to install a router and UPS in a storage cabinet in an RV type vehicle. In that case I think it's important to be reasonably accurate. As far as I can tell, this information isn't listed on spec sheets by Cisco, Motorola, or even APC, so I assume I need to calculate it myself some way.
Since the formula for power to heat is 1W = 3.41 BTU/hr my first pass at calculations was just to multiply the equipment power consumption by 3.41 to get BTU per hour. However, I guess that would only apply if the equipment were 100% efficient at being a heater. So my guess is that the correct way to calculate would be to use the power efficiency, η to calculate, where (1-η) x 3.41 x Watts = BTU/hr. For example if a 1000 Watt UPS has efficiency η=.9, then I would think its heat dissipated would be (1-.9) x 3.41 x 1000 = 341 BTU/hr. If this is correct, is there a rule of thumb for estimating the efficiency of certain types of equipment?