OK, I got to thinking about this some more this morning and dug out some notes from a recent project. Real-world heat gain data from electronics like amps is extremely difficult to pin down -- in addition to being somewhat dependent on the actual load being driven (at least for solid state amps; tubes should be a lot easier to figure out since they are more like incandescent lights), there is no guideline or standard for measuring heat gain of electronic equipment. It's all a little fuzzy, but I recently took a stab at guessing some realistic heat gain values while doing loads on a facility that included viewing rooms equipped with 5.1 surround systems. Keep in mind that all of this mumbo-jumbo is assuming that the equipment is located in a small closet with no ventilation (closed door, no air vent, ...) -- sort of a worst case scenario.

Assuming a fairly typical system -- five channel amp, 150W or so per channel, pre/pro, DVD, satellite or cable box, maybe a VCR -- the peak electrical consumption will be over 2000W. Not all of that is heat gain, and that consumption is the peak anyway. I ended up estimating (guessing -- gotta go with the SWAG sometimes) that a system like this might generate 1000W of heat. It could be even higher, but for the sake of argument even this ends up being a significant load. So we've got 1000W, which equates to 3412 BTU/hr (or about 0.3 tons of cooling load). If we plan to cool this by ventilating it -- drawing room air through and dumping the hot air somewhere else -- we want to establish some limits on the temperatures we'll allow. The entering air will be 75F (could be lower depending on where you have your thermostat set, but 75F is a safe value in a house), and I'd like to keep the discharge air below 90F if possible. With 3400BTUH and a 15F temperature change, the air flow required is approximately 210 CFM (cubic feet per minute; CFM = BTUH/(1.08*delta-T)) -- in a small, totally closed closet, that's a lot of air, over 1.5 air changes per minute in a 4x4x9 closet. A 1" undercut on the door will allow about 100CFM into the room, so a louvered door or door grille would be needed to get that much air in. The air could be discharged into an attic or to the out of doors, but you want to keep the discharge ductwork short to minimize the work required by the fan.

Bathroom exhaust fans range from 50CFM to 110CFM ( this fan , for example, will move 110 CFM and sells for around $50), and can be easily configured to discharge straight into the attic or to a louver or roof cap. Other exhaust fans (such as this one ) can be had that will go up to 210CFM pretty easily. PC case fans can move 35CFM (for an 80mm fan) to 75CFM (for a 120mm fan), but with no more than 0.10" of static pressure. An exhaust grille alone could generate 0.05" to 0.10" of static pressure drop, making it very difficult to get all this hot air moved anyplace very remote. "Wall wart" AC adapters could be rigged to power these fans; many people use such adapters connected to the accessory outlets of receivers to power small fans. A PC power supply could also do it, but the larger AC/DC transformers will add a lot of heat -- typical PC's produce around 100W of heat, due primarily to the CPU and power supply (with some also due to the hard drive and such). Adding 50W of heat from the power supply equates to over 150BTUH, or a 15%+ increase in load.

On paper, there's not much if any factor of safety in these numbers (the numbers could even be considered low, if the nameplate data is to be believed). In reality, I would guess that a safety factor of 1.5 or more exists in these calculations. If you had 100CFM+ of air movement (an undercut or louvered door and a decent exhaust fan) in a small, otherwise sealed equipment closet, you would probably be OK, and a week or so with a cheap digital thermometer in the closet to track temperatures would let you know for sure. In a freestanding equipment rack, simple openings in the rack or a 120mm PC fan powered by an AC adapter ought to be able to keep things under control. In any scenario, I'm assuming that you have the recommended clearance around equipment (especially the amps) so that they can get air in and out readily.

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