I read a website that says, "Zoning a single-stage system is always going to be a sub-par design." They basically say a zoned HVAC system is inherently bad if it is single stage. That kind of scares me because I not only have a zoned system, I have a system where a zone was added. When the zone was added the HVAC company said that my system had the "capacity" to add a zone. We were basically dividing up an existing space and splitting it into two different zones, not adding new space. However, the website linked above says specifically that adding a zone to a single-stage system is an especially bad thing to do.

My system has 4 zones and 2 heat pumps and two outdoor condensers/exchangers. One heat pump has one zone and the other has 3 zones. It has a bypass damper on the return of the 3-zone heat pump.

How can I tell if I have a single stage system or a multistage system? If I have a single stage system, should I be analysing it to determine if I should convert it to a multi-stage system?

  • It's not a universal disqualifier, but I'm always skeptical of information provided by those who are selling a solution to a problem they are informing me about. Is one zone uncontrollably hotter than the rest for you? – dandavis Sep 1 '20 at 22:15
  • I agree with dan. the model number on the outside unit we should be able to look them up. A single Speed multi zone can be efficiently run with or without an inverter driven outside unit. or Break the area up into multiple zones and the efficiency may increase but only if the unit was properly sized and installed in the first place. I have put single speed higher seer units in a multi zone system and my cost was over a thousand less than the multi speed system. How long will it take to pay back 1000 over the life of the unit? Answer it may never pay back that’s why they still sell 13 seer – Ed Beal Sep 1 '20 at 22:36
  • I take it we're talking about residential variable-air-volume zoning, here, basically? – ThreePhaseEel Sep 1 '20 at 23:31
  • OK I have to ask, are you satisfied with how your existing system is preforming? Why are you going through this exercise? – JACK Sep 1 '20 at 23:57

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