We are replacing our old AC and electric furnace with a heat pump and an electric furnace with variable speed blower. The decision we are struggling with is single stage vs multiple stage heat pump.

Our house has two levels, and the upper level is always HOT in summer without AC. The ducting to the upper level should be bigger but we can't change it. Our winters in Eastern Washington can be very cold and long, so we are looking at the HSPF rating more than the SEER. We are trying to decide between two Rheem systems:

Single-stage Rheem RPQL-036JEZ heat pump 13.00 EER, 15.50 SEER, 10.00 HSPF
2-stage cooling/3-stage heating Rheem RPRL-036JEZ 12.75 EER, 16.50 SEER, 9.40 HSPF

We like the higher ratings of the single-stage unit, especially the 10.00 HSPF, but wonder what we'd be giving up by not getting the multiple stage unit. Do the benefits of multi-stage outweigh the lower HSPF and the additional $656?

Thank you for the help!

1st of all I would reconsider the variable speed blower,since you know you have a prob. With duct system ,when it comes time to replace (and it will) it going to cost you 5 to 8 hundred bucks,and it won`t happen till after the warranty goes out
if you`ve never had a multiple stage HP you won`t be giving up anything (can`t miss what you never had)
myself I can`t see that you would get a 656 $ advantage
but this is just ONE mans thoughts on the matter,, I`m sure you will hear more.

Most dwellings have uneven heating and cooling needs, so a 2-stage compressor can match better to those needs. And coupled with a VS blower can provide nice savings and comfort.

However, if you already knowingly have ductwork issues a VS blower may not work correctly for you.

With the single stage heat pump, the first stage of heating or cooling would probably provide a higher efficiency ratio than when it is running full bore (stage 2).

Honestly, if they make one, I'd get a three-stage (three speed) compressor in a heat pump, or just wait for inverter compressors (continually variable speed compressors) to reap in huge energy savings and the unit will be super quiet when the demand is not high (won't annoy the neighbors)

Complete variable speed compressors along with the electronic variable thermostatic expansion valves and associated circuit boards are now being tested for possible real time pipe line in 2011 BUT the associated costs will have to come way down and the training will have to go way,way, way,up. One of these units is in the test chamber as we speak. SEER so far 26 but more can be done with a little more fine tune of the controls.

Unless you fix the duct work no matter what you buy will not work properly. Have you considered a separate unit in the attic or ? For the upstairs. This way the system will really work well and the upstairs will heat and cool much better. Naturally you can go down in size for the original unit on the first floor.

I know you have a short cooling season but comfort is always important to me especially in the bedroom area.