The trick is transferring the energy/heat from the air to the building materials and/or furniture. This is accomplished by blowing adequate amounts of air against the materials you are trying to heat. It is this impact, the air colliding with the materials, that transfers the energy/heat from the air to the materials.
You will notice that the materials closer to the fan will heat faster and to a higher temperature. This is because the materials that are closer to the fan are being impacted greater by the airflow from the fan. This greater impact is transferring energy/heat to the materials at a higher rate than to the materials that are farther from the fan.
Pointing a fan directly at the wall will transfer the most energy/heat to the wall. Point the fan angled at the wall and you reduce the collision between the air molecules and the wall. This will reduce the transfer of energy/heat from the air to the wall.
Pointing the fan downward transfers more energy to the floor than blowing the air horizontally across the floor. If you are trying to heat under carpeting, etc…, placing your fans pointing downward will accomplish this more effectively.
Without adequate air movement, you will not thoroughly transfer the energy/heat from the air to the materials. If you are trying to kill Bed Bugs, this can leave materials that are not close to the fans cooler, allowing the Bed Bugs to survive. If you are trying to evaporate water from building materials, a lack of energy/heat transfer can reduce the rate of evaporation as evaporation is an energy/heat based phase change.
Adequate airflow also eliminates stratification. Warmer air rises and this can lead to a layer of warmer air above a layer of cooler air. If you want the warmer air at the ceiling then using less fans is ok. Normally we want the warmest air blowing against the materials we are trying to heat. Using ample fans blends the warmer air from the ceilings with the air lower in the room. This creates a more even air temperature throughout the entire room.
In Conclusion:
The primary purpose of using fans to heat a structure is to transfer the energy/heat from the air to the materials and eliminate stratification. Use enough air-movement to heat materials evenly.