My son's condo has central heat and air, but when the heat setting is put on, there is very little heat being produced. The air coming from the registers is barely warm. Trying to get an idea of what the problem might be. He has installed a new thermostat, but that didn't help at all. Thanks

The thermostat will not fix this kind of problem. It is possible you have a defective heater element or a bad sequencer if so equiped.