The answer to 'what size surge protection do I need' is that the size of surge protection you need depends on the size and electrical needs of your home. As a general guideline, a whole-home surge protector rated for 120/240V, 40,000 Amps or more is recommended for most residential properties. This type of surge protector will provide comprehensive protection for your home's electrical system and connected appliances.
The size and rating of the surge protector you choose should be based on the total electrical load and number of circuits in your home. Larger homes with higher electrical demands may require a surge protector rated for 50,000 Amps or more. It's best to consult with a licensed electrician to determine the appropriate size and rating for your specific home and electrical needs.