First we tried a Master Flow 6000 CFM 30 in. Belt Drive Deluxe Whole House Fan with Shutter.
It looked to be well built, but we were a little unhappy by the low-frequency noise it produced (I would call it "choppy", which eventually convinced us to return it. Not so loud that you couldn't carry a conversation, to be sure, but annoying as a background sound while reading or using a computer, at least to me. This was with zero constraints airflow on the intake or output sides of the fan, they warn you it could be louder once it's installed and there's a limit on airflow.
Power use was 380 watts at 6000cfm; at the lower speed it was 290 watts.
Then we tried a MaxxAir 42 in. Industrial Heavy Duty 2-Speed Belt Drive PRO Drum Fan. Not really meant as a whole house fan, but if you box it in, why not? Slightly quieter, and it moved more air too (6000 cfm vs 95000 cfm). At 9500 CFM it drew 500 watts. At 13000CFM it drew more, I think about 750 watts, but I don't recall for sure.