Quote:
Originally Posted by JManc
AC/ HVAC units have a limited life span (10-15 years) so not unrealistic for people to replace them several times within their lifetimes.
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Windows and roofs also have a limited lifespan (about 20-30 years). So you might as well go with the option that provides the most energy savings over the long term. And if you are already doing that work, you might as well add insulation and air-sealing as well. There are techniques that allow you to add air-sealing and insulation in a non-invasive manner while the building is occupied (such as external continuous insulation).
And once you have made your building more energy efficient, you will see that you don't need replace your AC/HVAC equipment with new equipment at the the same size (BTU tonnage). In fact, installing an oversized AC is actually bad, because it will cool your space far faster than it can dehumidy the space, which makes the occupants feel cold and clammy. By reducing the size of the AC/HVAC that you need, you are saving a good deal of money upfront on equipment costs.