Just looked at your picture.

You want them as far away from that water heater as possible unless you live in a cold climate then the heat that is in that area would be beneficial to you.

If this is your only grow space you can have then push the plants back as far away from the water heater as possible. Take the oscillating fan out of the grow area and place it immediatley in front of the grow area facing your water heater. Lower the fan as low as it will get to the ground. Then point the fan as far up as you can angle it away from your grow area. Keep it on high and oscillating at all times.

Get 4 smaller stationary 2" desk fans. Or buy some 120mm computer fans and use those at each corner of your grow space for air circulation.

This will get your plants as far away from the water heater as possible. The fan will try as best as possible to lower the ambient room temperature/try to blow hot air away from the area.

Multiple smaller stationary fans should be adequate for air circulation and will allow you more room to move away from the water heater.