I have a customer that was quoted a 15 seer Carrier A/C and HP system added to his existing gas furnace. His home is new and he would like to keep his old furnace. I told him I did not think one could achieve More than 14 seer without replacing his furnace with a variable speed option. I know that ARI is the authority on this but I don't know the model of the unit he is quoting. We have also seen head pressure problems on high seer heat pump add ons to existing builder type gas furnaces with standard blowers. Any input would be appreciated.