Gas Smell coming from Heater?

I'm getting a strong gas smell when I turn on the heater? I just changed a few leaky injectors and ran the vehicle to try and clean the gas smell after the job was completed. That seemed to work just fine until.....Since it's getting colder, I turned on the heater (all levels) and get a strong gas smell? Where can I check in the heater for gas leaking into the vents? What should I look for and examine?

Thanks
Jason

The heater uses warm coolant in a tiny radiator to heat the air. so there is no gasoline involved anywhere in the heater system.

My guess is you have leaking fuel somewhere and the fumes are being drawn into the vehicle from the vent just in front of the windshieldor around the gaps where the hood hinges fold into the body where air fron under the hood can get into the heating ducts.