The 26-year-old Derby striker scored two in four outings in a loan spell last season and is back until January.
And Varney was immediately in the thick of it as Wednesday systematically destroyed Scunthorpe - manager Brian Laws' former club.
His early shot was saved by Iron keeper Joe Murphy but the home side scored from the resulting corner.
Darren Potter's deep corner found Tommy Spurr, who was stationed on the far post to head back across and centre-back Richard Wood nodded in from point-blank range.
After 12 minutes Varney cashed in on a slip by Rob Jones, skipped into the area again to pull back a dangerous ball.
Marcus Tudgay missed it but it fell for Jermaine Johnson, who drilled an unstoppable shot past Murphy from over 20 yards.
Wednesday continued to sweep forward and Varney headed down into the path Darren Purse, but the Wednesday skipper's snap shot was wide.
Scunthorpe were dealt a further blow when Jones attempted to head clear and clashed with Wood. The pair went down and after a long stoppage Jones was stretchered off.
Even worse was to come with Wednesday's third in the 34th minute. An accurate corner from Michael Gray over the crowded six yard box found Marcus Tudgay who rose above the rest and guided in his header.
Ironically it sparked Scunthorpe's first threats at the Wednesday goal. The visitors earned a corner sent in by Grant McCann, but Tudgay was helping out at the back and headed clear.
Another cross from McCann was aimed at Paul Hayes, but Lewis Buxton nipped in smartly to clear. And when McCann flighted in another corner Scunthorpe frontman Gary Hooper headed wide.
Potter added Wednesday's fourth in the 58th minute when he latched onto a half cleared ball and hit a blistering shot from the just inside the area.
And when Varney was substituted 20 minutes from the end he earned a standing ovation from the home fans.