Let's travel deeper.
1. Figure the actual percentage of wattage released into the air from a GPU.
EDIT: 6990's are rated at 375watts TDP; TDP is defined as the amount of energy the cooling system needs to remove from the IC for proper functioning
http://en.wikipedia.org/wiki/Thermal_design_power. So I would have to figure it would dissipate 375watts into the air at 100% PU usage.
2. Possible duty cycle of GPU heating system to keep house warm and not cook humanz alive.
3. Duty cycle will give us the cost of electricity
4. Duty cycle also gives us potential coins generated
5. Subtract electricity cost from coin value, hope its small!
(currently working on finding a good guesstimate of these)
It is far simpler. Computer components (including GPUs) do no "work" in the physics sense. So 100% of energy drawn from the wall will be converted to heat.
If you want a 3KW heat just build a rig (or rigs) which have a 3KW load. No other calculations are required. It doesn't matter where the heat come from (CPU idling, GPU core, VRMs, power supply ineffciency) it is all heat.
So for 1 it seems that all wattage is released into the air, further more pretty much all wattage consumed by electrical devices is given off as heat. We then need the minimum cost of a computer to run the maximum amount of GPU's at once and its power specs.
To calculate how much heat every 6990 in the setup will produce, you have to consider how much energy the computers containing them will draw from the wall. PSUs aren't 100% efficient, and all the "lost" energy gets converted into heat as well.
Calculating 65 W power consumption outside the video cards, we get a total of 1565 W for a computer holding four 6990s. If the PSU operates at 85% efficiency, the whole setup will draw approximately 1840 W from the wall, giving 460 W per video card.
By DeathAndTaxes view per 4 6990's we'll need 1565W from the wall. Producing 1565W heat output.
60kBTU = 17580W / 1565W = ~11 = 12 of these rigs
Now if this rig can produce out needed 60k btu, we need to figure the duty cycle of a regular heater at 60btu. Then at this duty cycle determine how much power our rigs would draw, and find the cost of it.
Any idea for a house heaters duty cycle?
-- If we are on a duty cycle they won't run 24/7 so hopefully they don't get abused to hard..
Also videocards were not designed to run 24/365
Even at modest settings something is bound to go off, be it a fan, or something worse. If you have no warranty then this is worst idea ever.