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Cooling Question

I am currently

looking at a job that has an extremely large furnace 120,000 btu's (two times the heat

load) but a properly sized single stage 4 ton a/c unit.

The homeowners would like to zone the house from top to bottom! The first floor load is basically two thirds the entire load.

I do not see how this would be advantages to them in anyway. Especially 

with bypass dampering the single stage 4 ton a/c system will short cycle

and not dehumidify the home properly.

Just looking for others input for or against my thoughts. Any information would be greatly appreciated


  • Difficult

    Hey Jamie!

    How are you doing?

    Zoning a house with a single speed compressor and indoor blower is difficult at best and should be avoided whenever possible. A dump zone could be installed, but there is no real benefit as you are just redirecting the air to an unused area.

    Now, you could incorporate a multispeed motor and a control system that will throttle the motor down when one zone is satisfied, but you are reducing the airflow through the evaporator coil without adjusting the refrigerant flow through the coil. You will be in danger of freezing the coil and, worse yet, liquid floodback to the compressor.

    Have fun and, in my opinion, steer clear!

    All the best to you and the entire family!
  • don_9
    don_9 Member Posts: 395

    Even if the ac is the right size with the furnace oversize you still had the same issue we have had for years in this field, getting the airflow down to 400 to 350 cfm per ton to match the ac equipment.

    I am going to share my thoughts on zoning,modulating equipment.After being in the field and testing and taking in consideration of service and part replacment i am now at the belief that single stage equipment with properly size distribution system is the way to go.Now dont get me wrong i dont mind connecting a two speed condenser on two airhandlers when we have limited space to sit outside equipment.Other then that i am slowly going away from all this high-tech equipment.

    i truly becoming a kiss kind of guy.And I also truly feel that my customer will fair much better as well.

    Jamie you know what the right thing to do is.Dont let the customer talk you into anything.Believe when it does not work you will be the blame.and rightfully so being you are the hvac contractor..

    Good luck.Hello professor hope all is well.Good to see you posting again.

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