There are a couple of reasons why heat recovery ventilation isn't optimal for older buildings. If you are trying to consider whether you should install this type of system, here are a couple of things that you need to keep in mind.
Reason 1 - Codes and Regulations
When working with older buildings you have to make sure that anything you do is up to code with the village or town. Many times, changing one thing will cause you to have to change another and building on top of an older structure can be stressful on the actual building. There is a lot of work that goes into making everything right and up to date and it isn't always worth it.
Reason 2 - Expenses and Updates
When it comes to making changes like this one, even if they are for the better, it comes with a lot of costly repairs and updates. If you find yourself changing one thing, you will also have to change other aspects of the building so that it is able to keep up and with the other parts. This can prove to be extremely expensive to continue to update things one by one to work together.