I have attempted to do research but haven't had much luck and am hoping someone here can provide some insite. I have a 2 story townhome, 2100 sq ft and currently have 2 ac units. Each unit handles a zone (downstairs/upstairs) The downstairs unit needs to be replaced.

I have had 3 ac contractors out and gotten a different answer from each. First answer: replace the 2 units (all parts) with 1 single unit. Second answer: replace the 2 units with 1 single heat-pump unit and third: only replace the unit in question.

So, given that this is Houston, Tx - is it recommended to have 2 units, is a heat-pump effective in Houston or do I have a different option?

Thanks all!

What type of heat do you have now? Also with out being able to see your duct work, can't say for sure but if it was set up for 2 systems sounds like it would be really hard to convert that to 1

I would replace only what's broken, a heatpump in Texas is probably a good idea
When set up correctly a heatpump can save you a bunch of $ in the winter time
As Joshdta stated changing from 2 units down to one will be a harder thing to do.
Stay with the 2 units