Even with a single stage HP paired with a var speed air handler, you will get better dehumidification in cooling mode but not as good if you have a 2 stage outdoor condenser. I would want dehumidify on demand set up if you live in climate with high summertime humidity. That will require the correct thermostat. I think this is more of a situation to weigh he cost difference vs benefits.

IMO

Thank you for the input, in fact all of the contractors did talk about the need for a thermostat with humidity control and included it with the new units. I do live in a very hot and humid state (Florida) so I guess it would make sense the extra investment in a variable speed A/H. Thanks

Single speed AC with variable speed blower will not dehumidify much over that of a regular single speed AC without the variable blower. It's probably closer to negligible because a single speed AC is over sized 90% of the time it runs.

It has a tendency to over cool in an attempt to dehumidify. All thermostats limit dehumidify potential to a mere 3 degree band. It will take no time flat in many cases to hit this set point with a single speed AC.

A variable speed blower typically adds 1 SEER efficiency to your AC. So if your outdoor unit is a 14 SEER then with a VS blower it becomes a 15 SEER.

However, a 16 SEER AC will not become a 17 SEER AC with a variable speed blower. The 16 SEER requires the VS blower to be rated at that 16 SEER rating. There are differences (usually slight) due to configuration / sizing of your system and so on.

A two speed AC set to run with VS blower and dehumidification thermostat will give you the best bang for the buck and much better dehumidification than single speed AC for the simple reason it will run in 1st stage 90% of the time and while in this mode will run longer because capacity of the system is reduced in this stage to roughly 70% of system capacity.

With that said, there will be times in which the 2 speed AC's dehumidification won't matter that much due to the temperature / humidity independence from one another. You can have 70 degree temps with high humidity and so most people won't run the AC during these times because it's too cold.

This is where Inverter Systems come in. They have the capability to dehumidify even better because they have 5 compressor run stages / with a few models having full variable cycling of the compressor.

The 2 speed AC systems are considered mid level systems with Inverter systems taking the high end category.

I see, that makes a lot of sense. I was almost set on getting one of this VS systems, but now that I know better I can see that it's not worth the extra investment. I'm glad that I took the time to research this a little further and I really appreciate your help in clarifying this issue and saving us a few extra bucks. Thanks again

There's nothing wrong with adding a variable speed blower system to a single speed AC, but that is not what the variable speed blower was designed for.

Variable speed blowers are required to obtain the higher efficiencies of upper end equipment 16 SEER or higher and manufacturer's trying to hit these higher efficiencies are required to limit or reduce capacity of the system's out put. In the realm of air conditioning this helps you more than it hurts you because the highest AC loads of the day are during late afternoon and early evening.

Typically from 3pm to 6pm and during extended heat waves this may extend from 3pm to 7pm.

Under normal circumstances if you take 3 hours divided by 24 = 8. That means 1/8 of the time the system runs it is sized properly. (regardless if it was sized properly according to manual J it is oversized outside this 3 hour span of time)

Under extended heat waves it jumps to 1/6 of the time. So if anything this shows you how complex this situation is.

With the examples above you can go a step further: 100 = 100 percent of time. Take that 100 percent of time and divide by 8 = 12.5 then subtract: 100 - 12.5= 87.5

Without seasonal influences /changes 87.5 percent of the time (normal weather) your single speed AC system is oversized. This is why a 2 speed AC system was built for a humid climate.

The other often over looked conundrum is that furnaces tend to last longer in climates that are more tropical, if you choose a variable speed system now and 10 or 15 years from now the AC goes south again you will have more options available to you when it comes time to replace the AC again. There isn't necessarily a right or wrong answer, it's just another decision you have to make.

I live in a humid climate... I service the Katy, Texas area. If you have similar issues at your house, I can put you back on the right track.

A system with a variable speed blower is better and a full variable speed system is mo better. It is hard to conceive of how much better the latter control humidity if you have not experienced it. Any HVAC system is designed to remove humidity at the expense of pure overall temperature lowering capability. Variable speed/capacity components make the system more multipurpose, they can be biased in either direction depending on the needs.