And the victory might have been even more convincing with the Bulls hitting the woodwork on three occasions.
Hereford were without skipper Tamika Mkandawire due to suspension while Barnet fared even worse with three - Barry Cogan, Magno Vieira and Liam Hatch - sidelined due to bans.
Despite this, it was the Bees who made the more lively start with a low cross from Jason Puncheon well caught by Hereford goalkeeper Wayne Brown inside the first 30 seconds.
United, however, came up with the first true opening on six minutes when the ball broke to Steve Guinan after Smith bustled into the area.
The on-loan forward struck his shot well but the ball smashed against an upright and came out.
After that, both sides struggled to create chances in a patchy period of play but Hereford suffered a blow when Simon Travis had to helped out with a nasty cut to his ankle. Andy Williams took his place.
On 34 minutes, Barnet had a great chance to take the lead when a slip by Dean Beckwith let in Giuliano Grazioli. Brown was out quickly to bring off a fine save.
Almost immediately, at the other end, Hereford had an equally good opportunity when Alan Connell headed wide from a fine Thomas cross.
Three minutes into the second period, Hereford took the lead when Guinan sent Ady Williams away on the right and his cross was bundled into the net by Smith.
Shortly afterwards, Guinan's header from a Trent McClenahan cross came back off the woodwork and Connell was similarly unlucky later in the half when he drilled a Guinan pass against a post.
Barnet had their moments and Grazioli will be kicking himself for missing the target from 15 yards when put clear by Oliver Allen's pass.
But Hereford sealed the points that their display had deserved in injury time when Guinan, who was always at the heart of the action, sent in a cross from the right that was rifled into the net by Thomas with a first-time drive.