can you explain what condensing means in regards to a furnace? and i’ve yet to witness a heat exchanger burn exhausted gas so that too if you will.
from the interweb, as it can explain it better than I can.
The higher- efficiency models are “condensing gas furnaces.†They run exhaust gases through a second heat exchanger to extract and use available heat that’s otherwise exhausted. These models pull out nearly all of the heat, sending cool exhaust out and leaving behind condensed water. This condensate, 5–6 gallons per day, is drained or pumped away.
the heat exchanger is not “burning” anything, just capturing the heat, not unlike, a heat pump.
the heat exchanger you speak of is the evaporator coil, nothing to do with a gas furnace other than it uses the same fan from inside of the furnace and the coil is connected to the furnace with the use of a transition (pretty much butted up to the furnace or you can get a coil-furnace combo in which if that is the case then the coil is in with the furnace in one box and has a drain coming from it but it’s still only in regards to the the coil, nothing heat as far as calling for heat via the t-stat or in plain english nothing to do with when the heater is ‘on’ and calling for heat but yes, the extraction of heat from freon in the coil is how you get cool) but rather the cooling side in regards to freon which condensates and is drained. no gas furnace on earth will produce a liquifiable and drainable to mother earth liquid. read far down and you’ll see that gas to air is direct and so the burners are the heat exchangers so to speak.
HVAC air coils
One of the widest uses of heat exchangers is for air conditioning of buildings and vehicles. This class of heat exchangers is commonly called air coils, or just coils due to their often-serpentine internal tubing. Liquid-to-air, or air-to-liquid HVAC coils are typically of modified crossflow arrangement. In vehicles, heat coils are often called heater cores.
On the liquid side of these heat exchangers, the common fluids are water, a water-glycol solution, steam, or a refrigerant. For heating coils, hot water and steam are the most common, and this heated fluid is supplied by boilers, for example. For cooling coils, chilled water and refrigerant are most common. Chilled water is supplied from a chiller that is potentially located very far away, but refrigerant must come from a nearby condensing unit. When a refrigerant is used, the cooling coil is the evaporator in the vapor-compression refrigeration cycle. HVAC coils that use this direct-expansion of refrigerants are commonly called DX coils.
On the air side of HVAC coils a significant difference exists between those used for heating, and those for cooling. Due to psychrometrics, air that is cooled often has moisture condensing out of it, except with extremely dry air flows. Heating some air increases that airflow’s capacity to hold water. So heating coils need not consider moisture condensation on their air-side, but cooling coils must be adequately designed and selected to handle their particular latent (moisture) as well as the sensible (cooling) loads. The water that is removed is called condensate.
For many climates, water or steam HVAC coils can be exposed to freezing conditions. Because water expands upon freezing, these somewhat expensive and difficult to replace thin-walled heat exchangers can easily be damaged or destroyed by just one freeze. As such, freeze protection of coils is a major concern of HVAC designers, installers, and operators.
The introduction of indentations placed within the heat exchange fins controlled condensation, allowing water molecules to remain in the cooled air. This invention allowed for refrigeration without icing of the cooling mechanism.
The heat exchangers in direct-combustion furnaces, typical in many residences, are not ‘coils’. They are, instead, gas-to-air heat exchangers that are typically made of stamped steel sheet metal. The combustion products pass on one side of these heat exchangers, and air to be conditioned on the other. A cracked heat exchanger is therefore a dangerous situation requiring immediate attention because combustion products are then likely to enter the building.
A condensing furnace