Outdoor stat why do I need one???

big_al_41April 30, 2012

Ok, I've seen many time here that one should think about an outdoor stat for their furnace etc ... my question is why?? I live in doors...LOL

I mean isn't my in door stat sensing what I need for heat where I actually live. Thanks please make it so a lay person will understand ..Thank You

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heatseeker

Usually used with heat pumps so tstat knows when to shut unit down outside and turn on heat strips or emergency heat.

    Bookmark   April 30, 2012 at 8:53AM
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tigerdunes

Big al

Two major reasons come to mind.

1. If you have thermostat that has capability of displaying outside temperature at the thermostat.

2. Main reason though is for dual fuel application like heat pump with backup furnace. With the correct thermostat and outdoor sensor, homeowner can be in control of changeover point between HP and furnace.

Disagree with previous post. You don't want to disable a HP for electric heat strips unless it is a very low outside temperature. Most people run their HPs just fine without an outdoor sensor.

IMO

    Bookmark   April 30, 2012 at 12:20PM
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ionized_gw

Some hydronic heat systems are set up to modulate the boiler set point with outdoor temp. OP wrote "furnace", but often that is used for boilers.

    Bookmark   April 30, 2012 at 2:15PM
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heatseeker

whaaat?

    Bookmark   April 30, 2012 at 2:28PM
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mike_home

There are some thermostats which use the outdoor temperature to determine which stage of the furnace or AC/heat pump to use as part of the decision algorithm. You also may have options to lock out a low or high stage depending on the outside temperature.

    Bookmark   April 30, 2012 at 2:29PM
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saltidawg

tigerdunes,

Not disagreeing, just don't understand.

"Disagree with previous post. You don't want to disable a HP for electric heat strips unless it is a very low outside temperature."

    Bookmark   April 30, 2012 at 4:25PM
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tigerdunes

OK Salti

You don't need an outdoor sensor on a traditional all electric HP system with air handler and backup heat strip for both supplemental heat, to temper air on a defrost all, and emergency heat when outside HP condenser as malfunctioned for whatever reason.

The only exception that I can think of is at extremely low outside temp where HP heat produced is less than a COP of 1. This means it is costing you more to run the HP condenser than the heat(BTUs) produced.

Hope this helps.

I generally agree with Mike's post although this gets into high end systems with high end controls that can do every thing but dance.

IMO

    Bookmark   April 30, 2012 at 4:53PM
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saltidawg

tigerdunes,

Got it! Tnx.

    Bookmark   April 30, 2012 at 8:42PM
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brickeyee

The outdoor unit is not a complete thermostat, but just a sensor.

    Bookmark   May 1, 2012 at 4:11PM
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