The cost and markup on variable speed units means that the return on investment is likely to not be any better than getting a single stage unit. For people in high humidity areas, the variable speed unit may be better for humidity control. Also, if the customer lives in a hot climate, a variable speed unit may spend a lot of time running at or near the highest speed, meaning that it is not working much more efficiently than a two stage unit or even a single stage unit. Also, if there home is on a utility with tier priced electricity, it becomes harder to justify the variable speed unit because while they can be much more efficient in mild to medium temperatures, since the electricity is likely being priced in a lower tier rate, the savings are going to be much less. I have run spreadsheets on all types of systems based on my own monthly consumption, and in my case, the return on investment for variable speed systems simply wasn't there, but a two speed system did beat out the single stage unit, though the savings will not be all that great. It should keep the house a bit more comfortable though but I just could not find a scenario for my own tiered rate structure and super hot summers that made the variable speed cost worth it. It is a big decision to make because you can spend as much on a new AC and furnace as you spend on a nice used car, and when spending this kind of money, one should really look at their utility bill over a year and see if the unit will ever pay for itself. The on line calculators typically don't have a mechanism to deal with tiered electricity pricing, so if you are tiered, expect to not save nearly as much on a variable speed unit as the calculators suggest you will save.
I have a 2 story home with a smaller and larger ac unit. Is the single stage good to get? The smaller is for upstairs and the larger one is for the main level.
