It might seem odd to think that a gas furnace would need a drain hose, but this is the case from time to time. Air conditioner units regularly need drain hoses or some type of drainage system to remove condensate from the system. The same can be true of certain types of furnaces.
Drainage pipes or hoses are needed for condensing gas furnaces because these furnaces create byproducts that can be harmful to the operation of the system. This process takes place throughout the entire combustion process. Many condensing gas furnaces have a stainless steel secondary heat exchanger that produces a form of condensate that is acidic in nature. Total Air Supply notes that the byproducts produced are not necessarily harmful in and of themselves, but can be when the combustion process is not fully completed.
Drainage of condensate from a gas furnace is closely tied to the ventilation of the system. Much of the harmful byproduct produced by the combustion process occurs throughout the entire combustion and ventilation process. In other words, some combustion continues to occur even in the final stages of ventilation. Not all of the ventilation process can remove the condensate, however, and that element that remains behind must be drained from the system and not be allowed to accumulate.
Drainage of the condensing gas furnace is necessary because the combustion process occurs throughout the system and not all of the byproducts are able to make their way through the ventilation system. Total Air Supply notes that the process of ventilation creates the need for drainage. Water vapor condenses within the vent pipe and drains back down into a trap where it is pumped and drained away from the furnace. In some cases, two drains are used. One goes from the heat exchange to the trap, while the other goes from the ventilation system to the trap.
In high-efficiency furnaces where drainage systems are needed, it may be necessary to occasionally troubleshoot the drainage system in cases where the furnace is not putting off heat. If the hose becomes kinked, this could cause the system to malfunction, so it may be necessary to ensure that this has not occurred. The drainage to the outside of the house should not be blocked either as this could cause condensate backup in the system. When condensation forms and freezes on PVC drainage pipes, you may need to pour boiling water over the pipe to eliminate the frozen matter and free up the pipe once again.
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