HVAC Question

If you are running an industrial operation where pennies add up to millions quickly, go with highest seer multi-stage system you can get.

If you just want your house to be cooled, seer 14 will work and be efficient.

Seer isn't the only thing to look at though. There's a rabbit hole you can go down, if you want.

Pros and cons each and there is truth in the all the comments by the HVAC persons in your OP. Keakar was a HVAC guy so listen to what he says. The more expensive, highly efficient units are not necessarily more reliable, and expensive to repair. By the time you break even on the upfront cost it may be time to replace the system (13-15 years) so your main consideration with a more expensive, high SEER, multistage system should be comfort and humidity control they offer, and not potential long term cost savings that may not be realized on your part.

Another option to consider is a 14 SEER Single Stage HVAC coupled with a whole house dehumidifier, which will regulate your humidity during periods, fall/spring, when your HVAC is not operating much or even summers during pro-longed rainfall events.

16 single

Can you get a 2-stage, 14 or 16 SEER unit?

When I was talking to guys, 16 was the highest rated single stage you could get. The cost from 14-16 was pretty small. But the jump from single stage to 2-stage was more significant. So if you want the 2-stage operation, that’ll drive the first consideration.

At times I do wish I had a 2-stage system because I struggle with humidity levels. I bought a portable dehumidifier that has done wonders ($180). I only run it when it’s needed so it’s not too bothersome. I wish it had a smarter control so I could trigger it with my ecobee.

Insulation and other factors are much more important IMO.

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Do two stage units have problems and leave moisture inside of the ductwork like I've been told, causing mold problems?

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I think the potential for moisture issues in ducts is more likely associated with multi-stage vs 2-stage HVAC units. If for example you had a 4-ton 2-stage, the 2nd stage will be operating at 70% of max capacity much of the year, equivalent of a 3 ton unit, but still a large volume of cool conditioned air moving through your ducts. A 4-ton multistage unit may have as few as 5 stages (Carrier/Bryant) or as many as 700 stages, so the unit may be operating the equivalent of 0.75 to 4 tons during various times of the year depending on the heat load in your home.

If you have a “traditional” vented attic with standard fiberglass insulation (as opposed to spray foamed semi-conditioned attic) temps can hit 130 F in the peak of summer. Conditioned, cool air moving through the ducts at slow speed with a multistage unit can reach dew point before reaching the vents causing moisture to form in the ducts if there is duct leakage and/or the ducts and air handler (if in the attic) are not properly insulated. This not likely to happen in a sprayed foam closed attic where temps are much cooler. The potential for condensation in ducts is also higher with multistage units for those who keep their house cold, say 70-72, as opposed to 74 or higher.

I for one would not consider a multi-stage HVAC in a traditional vented attic without having my ducts checked for leakage and the leaks repaired if necessary and insuring the ducts are properly insulated. I don’t think these issues would likely occur with a 2-stage HVAC operating at 70% of max capacity because a large volume of conditioned air is still moving rapidly through the system at all times before it reaches set point and shuts off. On the other hand a multistage system may be operating nearly 24 hours per day in the heat of summer and you may not even know it because they are incredibly quite.

Source of my information, Paul LaGrange, forensic building inspector, who does the Home Improvement Show, WWL radio New Orleans, 9-11 am on Saturday’s. He has answered this question many times on his radio program. Call his show and ask him to explain, or you can text your question, and he’ll read your text and explain. But if you call, he’ll ask you questions about your house to help you decide LINK. He is a strong advocate of multi-stage HVAC systems but only if the house/attic/ducts are properly insulated to accommodate them. He is also a strong advocate of whole house dehumidifiers in the Deep South/humid climates and he thinks they are underutilized in our area of the country.

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I just accepted the Bryant 17 SEER 2 stage bid. Hope they get installed by June

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Sounds like a good choice particularly at the price quoted compared to the 20 SEER multistage system. Was that $17K for 2, 3-ton units? Or = $8,500 per 3 ton unit? If so, that is a lot cheaper, like $5K cheaper, than the quote I was provided for a 2-stage 17 SEER Trane.