There are ways to do things that are less noticeable.

For example, Monticello has air conditioning.  It was not put in by Mr. Jefferson, obviously, but some time later.  It is composed of very small duct work, and small holes, about 3" in diameter, in the corners of ceilings which are hardly there.  It is a very good job!

Then, there are the other kinds of installations which leave much to be desired.

The other day I did an inspection on a 100 year old farmhouse.  In its day, it was a lovely place.  Years of deferred maintenance have created many problems.

Over the years they have made improvements. 

One such improvement was air conditioning.  A good idea and a necessary one.  With a metal roof, and poor attic insulation, it gets real hot in there!

To the right is the corner of the master bedroom.

A new AC unit was put in the attic and duct work run throughout the house. 

It is not exactly invisible.

Nor is this one.  This is in the corner of the closet in that same bedroom.  Not the prettiest installation.  The other problem is that it takes up about 1/3 of the closet. 

Closets in 100 year old houses are not that large to begin with!

Taking up a third of it with invisible duct work might not be the best way to handle the improvement.

The second bedroom has just as fun, and aesthetically pleasing, an installation.  Hidden unobtrusively, you can hardly tell it is there! 

The floor was attractively cut out, as well as the ceiling, and it is deftly held in place by well-placed braces.

OK, this has all been tongue in cheek, but it might be part of the reason that this house has been on the market for over a year. 

When improvements are made, they really should not be slip shod, spur of the moment or done unprofessionally.  Everything that goes into a house makes up its appeal when it goes on the market one day.

My recommendation:  think things through before improvements are made to your house.  And be sure your improvement is done in such a way that another would want to buy it!