I'm replacing a 20 year old Lennox two stage heat pump. Live in northwest Florida panhandle. 2400 sq foot single story home. One AC tech suggested not using a two stage replacement unit because of cost. What are advantages of two stage over single and what should I consider in choosing replacement unit?:confused:

Cost comes in two forms. Initial cost and payback cost.

2 stages is like having high and low speeds or high and low heat transfer rates rates. A simple way of looking at it is if the desired temp and measured temp difference is small it, uses the lower rate of transfer. This potentially has the ability to reduce your operating cost.

When the temperature difference is high or it takes a long time to achieve a meaningfull change in temperature, the higher transfer rate occurs.

Examples for illustration purpses only:
It's 50 in the house, the HP was off and you set it to 72. High rate.
The HP has been running for 2 hours straight and hasn't shut off - High rate.

It's 72 in the house and the temp droped to 71, low rate.

You can save a bunch in energy, the question being when will the paypack occur. In Florida, I think the payback would be very fast.

You have to look at how long the new system might be expected to last, how long your going to be there, energy costs, payback time, initial cost and SEER and how often your using the heat pump.

So, if you kept your house at 76 deg, year round, I'd be looking at a 2 speed HP with the highest SEER.

If you rarely use it in the summer and winter, then your payback period would be very low. Minimum SEER and single speed.

You should be able to get a table of relative operating costs based on SEER from the manufacturer. They may also have a table for your area with single and 2 stage.