Temperature differential between thermostats on 3 zone system

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drbubba1995

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I live in Southern AZ in a 2200sqft single floor house. It was built in late 2014 with one unit in the attic and 3 zones in the house each with their own thermostat. The area in one of the zones is rarely used and I'm wondering about what temp that thermostat needs to be set at relative to the other ones. I've been told that all thermostats should be set to within 1 or 2 degrees of each other but if that is the case I can't see the benefit of the 3 zones. I have no experience with HVAC systems and am hoping someone can give me the actual facts on temperature differences among thermostats. Thanks for any info.
 

John Gayewski

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The zones aren't made to be different temps the only reason an ac system is zoned like that is to be sure cooling is even thoughout the house. Basically telling the ac to kick in if any of these three areas get hot. Rather than having only one spot in the house monitoring the temp you'd have three.
 

Fitter30

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Have no idea what zone system you have but a zone system is to have more even temperature or separate the bedrooms from the rest of the house for better temps at night or day.
 

WorthFlorida

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If any zone is separated by a wall and closed doors, that area can be set higher to any temperature if the zone is seldom occupied. If there is a return grill, that warmer air will be returned to the air handler and if there are jump vents, required code in Florida, it will pull cooler air from the other zone. Most homes there is only one returned grill per unit, not zones but you may have more than one return grill.

Open area zones one may be warmer than the other due to window and sun exposure. Two goals is not to over cool one area where by the heat from the warmer side will travel to the cooler side, therefore one zone will run more often. However, with one unit with multiple zones (standard AC air handler) are controlled by dampers? It will be a balance act not to restrict too much air flow otherwise the coils will freeze over in the air handler.

Multi level floors is another balancing act. I had two AC units one for each floor with a fairly open house plan. With both AC units set to the same temperature, the upstairs unit would run 24/7 becuase it was also handling heat load from the first floor. To balance out the load on the AC units, I has to set the upstairs 3º higher than the first floor so the first floor ran enough to cool down the master bedroom, closet and bathroom.

As you learned no more than 1-2 degree difference is about right but you can try at least 3º depending on the source of the heat load. To save energy cost increase the temperatures by one degree until it feel uncomfortable. My home in Florida, winter temperature I set the thermostat to 75-77 degrees mainly to control humidity, Right now in our summer weather patterns, 78 is all that is needed for a comfy home.
 
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