On Mon, 18 Jun 2012 18:18:30 -0400, "Percival P. Cassidy"
wrote:

Our home has a Lennox HVAC system installed by the previous owner a
little less than 10 years ago. The A/C unit has an SEER rating of
approx. 11, which is low by current standards. How practical and
cost-effective is it likely to be just to replace the condenser and
compressor units and keep the existing plumbing? And what about adding a
heat pump for winter heating (or pre-heating of the air before it gets
to the furnace)? This is in W. Michigan, if that makes a difference.

Perce

I cannot speak to the heat pump. In order to match the SEER rating for
the compressor and the furnace, they should both be replaced at the
same time... a matching set. It's what I had done after 12 years of an
older 10 SEER rated unit.

YMMV.