Do I Insulate Windows

[Missy H.]

Hi BP

I recently bought a duplex in March and inherited the tenant downstairs who has been there for about three years.  They are a nice older couple with a college age son.  They are respectful, keep a clean house and pay their rent on time.  It is an older house with old windows.   

A few months ago, the tenant (wife) asked me to replace the windows.  I told them no because the windows work and are not broken.  A few weeks ago, the tenant (son) asked me to insulate the windows because it gets cold in the winter and their gas bill is too high.  

I know that the previous owners did not insulate the windows because I did not see them on the windows when I initially inspected the property back in January / February 2016.

Would you insulate the windows?

Would you not insulate the windows?

Would you buy the kit for them and have them insulate their own windows?

Would you think about replacing the windows?

The upstairs tenant has not complained about the cold or the windows.  

Your thoughts are appreciated.

Thanks Missy