# Blehhh furnace question



## Smitten_kitten (Sep 8, 2011)

this might be a foolish question but it is one that is confusing me. I do not know how a furnace can both heat and cool. This is a brief synopsis of what i do know.
I know that a furnace is designed to take the heat produced by the burning of a fuel and transfer it throughout a home via a series of duct. the fuel is shot through a heat exchanger while it is combusting and producing heat. This combusting fuel source heats up the heat exchanger and then a blower blows air across it and into your house via ducts to each room. ( this is just a brief overview i know their is much more to the sequence of operation)

Ok I also know how a heat pump work and how it uses refrigerant to take advantage of the energy released durning phase change to heat and cool a home. I know that in order to do this their must be an evaperator, compressor, condensor, and pressure meteoring devices. Ive assisted in the installation of mini splits before aka ductless ac and i totally get how the system both heats and cools .

Now my problem is how can a furnace both heat and cool a house when their only built for heating? Would you have to buy a furnace that has an Evaporater coil in it. Would the furnace need to be attached to a condensor and have refrigerant lines run to it. Or would you just purchase furnace and stick an evaperator coil on it, connect it to a condensor and then you got a furnace that both heats and cools.

I have heard of a hyrbid system (heat pump and furnace) but what is the point? a regular heat pump can heat and cool a house why add the furnace too?

I hope this isnt to confusing to understand!


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## incarnatopnh (Feb 1, 2011)

Almost any furnace can cool as well. The evaporater coil is mounted in the plenum and the line set is run out to the condenser. Basic AC concept. Not trying to slam anyone as I know not all plumbers handle HVAC.


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## TX MECH PLUMBER (May 27, 2011)

If it's only built for heating it can't cool !!! If it's central heat and air then it does both or heat pumps do both!! To cool you always have a coil and freon ect, ect, to heat you have a gas fired heat exchanger, a heat pump or a electric coil .... I think you are over thinking this one. Why do you ask ???


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## Greenguy (Jan 22, 2011)

You could have your furnace run on fan only it would balance out the heat a bit take some of the cool air from the basement up stairs. But as stated above all a furnace really consists of is a fan with a heat exchanger of some sort gas or electric or water based.


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## wundumguy (Apr 3, 2010)

Smitten_kitten said:


> Or would you just purchase furnace and stick an evaperator coil on it, connect it to a condensor and then you got a furnace that both heats and cools.


The board on a modern furnace is typically designed with the control logic for extras like A/C coil, electronic air filter, and humidifier. Generally, extras can be added to an older furnace, but may require additional control components, or a board that supports extras.



> I have heard of a hyrbid system (heat pump and furnace) but what is the point? a regular heat pump can heat and cool a house why add the furnace too?


An air source heat pump operating in heating mode, "draws" heat from outdoor air. It is most efficient when outdoor temperatures are higher. As outdoor temperature drops, at some point it becomes more efficient to fire the gas burner or energize the electric strip heaters. These systems can run the heat pump in mild conditions and go to the gas burner in cold conditions. Exactly when that happens can be fine tuned to account for the heat output of burner vs pump at x temperature against the cost of gas vs. electricity. In some regions/climates, peak heat demand is much higher than peak cool demand. In these regions, a system that is adequate for cooling may require an additional heat source such as electric strip heaters to satisfy peak heat demand.



> Now my problem is how can a furnace both heat and cool a house when their only built for heating?


There are commercial furnaces (though there is no reason they can't be used in a house) that are designed like an air handling unit with fresh, exhaust and mixed air dampers. In milder climates, these units can provide adequate cooling without the addition of a refrigerated system.


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## Mississippiplum (Sep 30, 2011)

Here all we have strip heat built into the handlers. But we only run the heat in most houses 2 times a year. So a hp is unneeded or a furnace with evap coil


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