[pandaman]

I don't think you can get a variable speed system at the same price as a single speed one or even close to that: it's different, more complicated hardware. And, as it is already more expensive, they don't make variable speed versions of the cheapest designs hence they use more expensive materials and processes in the production (sound insulation, fancy finned coils, weather protection and such).

[criddell]

Do you know if a variable speed system will let you oversize and avoid the typical problems from doing so (short cycling, failure to dehumidify, etc...)? I haven't been able to find out a definitive answer. It seems like it wouldn't take a very smart thermostat to measure humidity and cycle times and throttle cooling to ensure that both factors are accounted for.

[pandaman]

I don't know, sorry. You better to talk with an HVAC installer. Perhaps your issue is that your system is not sized right from the beginning, did you get a schedule J or got the tonnage from the previous install/square footage?

[criddell]

I have talked to two different HVAC companies and our system is sized correctly. When I complain that when it's 105 out I'm lucky if it can hold 80 they tell me it's working as expected. They say no system can do more than about a 25F drop but I have a hard time believing that. People in hotter climates somehow are able to cool their homes more than 25 degrees and commercial spaces (like stores and offices) somehow manage to cool more than that.

On the other hand, I'm asking them to sell me something that's more expensive and the fact that they don't want to tells me that they have some reason to believe I wouldn't be happy with the result.

[pandaman]

It costs money to do a schedule J measurements so it's unlikely you've got it from just talking. What you describe sounds like an undersized system. Max 25 drop is obviously false, I have solid 75 with 115 outside with a residential AC, for example.

[criddell]

We've paid $225 for the consultation.

The max 25 drop does seem to be a widely reported thing. For example, my first search result for "max ac drop" is this:

https://www.jerrykelly.com/blog/how-many-degrees-cooler-can-...

[pandaman]

The explanation in the article does not make sense to me unless it's talking about window units. Ducted systems do not cool the outside air so the amount of temperature drop in the air passing through is not relevant. As long as it can cool faster than the air is being heated inside it can drop the inside temperature to the temperature of the coil, which is unlikely to be set at 80 degree in your case.