Here's why:
* Capacity Mismatch: A 5-ton condenser is designed to handle the cooling load of a 5-ton system. Three 1-ton furnaces combined only provide 3 tons of heating capacity. The condenser is vastly oversized for the heating system, leading to inefficiency and potential damage. The condenser might short-cycle (turn on and off frequently), leading to premature wear.
* Airflow Imbalance: The airflow needed for a 5-ton condenser is significantly higher than what three 1-ton furnaces would provide. This imbalance will also reduce efficiency and likely lead to freezing problems in the evaporator coil.
* System Control Issues: You'd have no way to properly coordinate the operation of the three furnaces with the much larger condenser. The system wouldn't integrate correctly.
To have a properly functioning system, you need a heating system that matches the capacity of the 5-ton air conditioning unit. You need a 5-ton furnace (or a heat pump with equivalent heating capacity). Replacing the furnace or the entire system would be necessary for a correctly sized and efficient system.
