Power consumption and electricity costs. I can't justify running it in the same season and at the same time as my (already struggling) air conditioner.
Well
@Doq, I suspect you may be being a wee bit over cautious here.
A fully loaded G5 Quad could conceivable draw up to 500W continuously if it is doing something strenuous, like PPCPorts builds. That equates to around 4 Amps of electricity at the 120v household circuit it plugs into. Now that average household circuit can provide up to about 12 Amps, which other household appliances may already draw - for example, your coffee pot may draw that much when you first start it up and it is quickly heating the water.
Your Air Conditioner, on the other, draws between 2,000W and 3,000W continuously while it is running. That equates to around 8 to 12 Amps at the 240v circuit they are usually powered by.
So, 500W vs. 3,000W... That is nearly an order of magnitude difference. I would argue that the impact of that extra 500W on your power bill would be fairly low. Mathematically, it would be only a 17% increase. If your monthly power bill (with air conditioner running) was, say, $350, with the G5 Quad running full tilt for the same billing period, that bill would only increase by $60... and that is only if the G5 Quad ran at 100% capacity for 100% of that time. Neither of those conditions would apply to real world use of the G5 Quad, even for builds however, so I would guess that theoretical $60 is more like $30 - $40.
So... Perhaps you could bring your G5 Quad out of its summer hibernation and put it back to work? The cost is low (ish), and a Quad is THE way to get this stuff done!
p.s.> All of the above assumes a typical household central air set up. If you are working with window or room air conditioners, then "all bets are off"; I would see your point entirely!