I thought I post an interesting little case report. Background: 5200 sqf old farmhouse This is the coldest property we have, at higher elevations about 50 min south of Buffalo, a couple years ago this was at -26.8F. Installed a 6 ton dual stage Climatemaster TT27 in 2009, reduced the heating bill from $5000 (propane) to $1800 (increase in electricity), dual pump flow enter (2x 26-99) http://welserver.com/WEL0447/ Customer's son got a variable speed 7 series a couple years ago, http://welserver.com/WEL0834/, now the father wanted one too. Now we replaced the 8 year old dual stage 6 ton with a new 5 ton WF 7 series with a single 32-140 variable speed flow center. Interesting to compare the performance. With very similar heating degree days, the daily KWH usage went from 110 down to 70, about a 35% reduction. Even more interesting, the balance point was around 20F for supplement heat, but so far, despite 10F night, the supplement heat did not engage, so it appears that we are getting a higher capacity out of it. An anecdote, not more, but interesting to see the evolvement of the technology in the last 7 or 8 years.